Treating Achondroplasia: ten years online. A review of the current achondroplasia therapy landscape

Ten years in a row

The blog Treating achondroplasia is celebrating 10 years online. I have not been posting as often as some years ago but I keep my eyes open to all new relevant information that comes to the field and share them with the interested reader here. 

Ten years ago, I started this blog with the main objective of translating the hard jargon that is typical in scientifc publications into a more relatable language that could be accessible to all. The blog has received more than 430K visits since its launch and I hope it has been a helpful source of information for you.

So, to start this new year (I know, it's already February) I want to share with you an updated review about therapies for achondroplasia that I prepared for Fundación Alpe (Gijón, Spain). Alpe is one of the world's strongest advocacy groups for acondroplasia and skeletal dysplasias and you can find the original article translated to Spanish here. This review provides you with high level information about all drugs that are known to be (or could be) in clinical development for the treatment of achondroplasia. You can find more details about them here in the blog: you just need to search for them in the index page.

Nevertheless, the research for therapies does not stop with the drugs listed in Table 1 below. New therapeutic approaches are being explored that we will be reviewing in the next blog's article.

Thank you for your interest in the Treating Achondroplasia blog!

An update of the therapies for achondroplasia

Note: this review has been prepared originally for Fundación Alpe.

Achondroplasia is the most common form of short-limbed dwarfism. This skeletal dysplasia is caused by a single point mutation in the fibroblast growth factor receptor 3 (FGFR3) gene, which in turn encodes the protein FGFR3, which is located across the cell membrane of the chondrocytes (1). Upon binding of its ligands (the FGFs), it is activated and drives several important cell functions (Figure 1).

FGFR3 has a key role in bone development by regulating the growth plate cartilage function. FGFR3 helps regulating bone growth by, like a brake in a car reducing its speed, counteracting the effect of many other agents which, as the car accelerator, promote bone growth (1). Without FGFR3, bones would elongate without control causing several medical complications (2). In achondroplasia, however, because of the mutation, FGFR3 is working a little too much thereby impairing bone growth (1). More potent mutations in FGFR3 lead to significantly more severe, sometimes lethal forms of skeletal dysplasia.

The consequences of the FGFR3 mutation are well known and go beyond the short stature typical of achondroplasia. Sudden death and neurological problems in early infancy, sleep apnea, recurrent ear infections and multiple orthopedic complications among others throughout life, not to mention significant impact on the quality-of-life, have been already extensively documented in many studies (3,4).

Since the mutation was discovered much has been learned about how it causes achondroplasia. Scientists started thinking and investigating how to control or reduce the activity of FGFR3 to help restoring bone growth. For instance, one of the first objective attempts to target FGFR3 for the treatment of achondroplasia was explored by the group led by Dr. Avner Yayon, who developed an antibody that could block FGFR3 and its activation (5). Unfortunately, FGFR3 works, as we saw above, in the growth plate cartilage, a very special tissue located within the very ends of each of our bones. The growth plate cartilage is a dense tissue that does not receive direct blood supply and these singular features prevent large molecules to transit inside it. As antibodies are very large molecules, in contrast to their vast use in treating many other diseases and in particular cancer, they couldn’t reach their target (FGFR3) in the growth plate, making them inappropriate for the treatment of achondroplasia.

Nevertheless, as scientists were mapping the chemical reactions driven by or affecting FGFR3 (Figure 1), they learned about many other bone growth-promoting agents, too. For instance, they learned that the C-type natriuretic peptide (CNP) pathway plays a key role in bone growth and that it also antagonizes FGFR3 in growth plate chondrocytes. Increasing CNP levels in the growth plate restores, at least partially, bone growth (6,7). With this knowledge in hands, vosoritide has been developed (8), followed by TransCon-CNP (9).

Figure 1. Pharmacological strategies targeting the FGFR3 pathway in the chondrocytes.

 

Modified from Matsushita M et al. 2013 (10). Reproduced here for educational purposes only.

As FGFR3 may play important roles in some types of cancer, scientists have tried to block it with molecules called tyrosine kinase inhibitors (TKIs) which have the ability to “turn it off” or deactivate it. It was natural to think that a TKI could be explored in achondroplasia. Actually, two of them are in development for achondroplasia (see below) and others might follow the clinical development path (Figure 1).

Scientists also paid attention in how FGFR3 is activated and if it was possible to prevent it. This resulted in the design of molecules like recifercept, a modified FGFR3 molecule that can circulate free, capturing the activators (FGFs) before they reach out to the genuine FGFR3. Using the same strategy, another molecule called aptamer was designed to do the same job, blocking one of the key FGFs before they turn on FGFR3 (Figure 1).

You can find a list of the pharmacological agents being explored for the treatment of achondroplasia on Table 1 and more details about them below.


Table 1. List of current and potential therapies for achondroplasia.

Name	Type	Developer	RoA	Frequency	Status
Vosoritide	CNP analog	Biomarin	SC	daily	Approved
TransCon-CNP	CNP analog	Ascendis	SC	weekly	Phase 2
Infigratinib	TKI	QED	oral	daily	Phase 2
Recifercept	Ligand trap	Pfizer	SC	daily	Phase 2
Meclizine	Anti-histaminic	Nagoya University	oral	daily	Phase 1
RBM-007	FGF2 Aptamer	Ribomic	SC	NA	Phase 1
SAR442501	Antibody	Sanofi	IV(?)	NA	Phase 1
ASP-5878	TKI	Astellas	NA	NA	Pre-clinical
ASB-20123	CNP analog	Daichii-Sankio	NA	NA	Pre-clinical

CNP: C-type natriuretic peptide. RoA: route of administration. SC: subcutaneous. TKI: 

Vosoritide

After long years of clinical development culminating with a successful phase 3 study (11), vosoritide, branded as Voxzogo, has been approved for the treatment of achondroplasia in 2021. In Europe (EMA countries) and Brazil, vosoritide has been approved for children two years of age and older while, in the US, the Food and Drug Administration (FDA) authorized the treatment for children from five years old onward. Other countries will soon follow suit.

Beyond the phase 2 and 3 studies in older children, Biomarin is also testing vosoritide in other three clinical trials, one in infants (NCT03583697), one in children with achondroplasia at higher risk of clinical complications (NCT04554940) and also in a study with other selected forms of genetic growth disorders (NCT04219007). 

TransCon-CNP

The main difference between TransCon-CNP and vosoritide is that TransCon-CNP is delivered through a slow-release system allowing a weekly dose with sustained exposure to their analog in contrast with vosoritide's daily dosing. In pre-clinical studies they showed that their CNP analog was superior to vosoritide (9).

Ascendis Pharma is conducting the phase 2 study ACcomplisH with TransCon-CNP. During the JPMorgan 2022 Healthcare Conference in early January (Figure 2), they reported that TransCon-CNP has been well tolerated during the study, with already 65 weeks of drug exposure. They plan to release the data from the phase 2 study in the end of 2022.

Figure 2. ACcomplisH study design (from Ascendis’ JPMorgan 2022 Healthcare Conference presentation).








Infigratinib

Infigratinib is an oral molecule initially developed to treat several types of cancer where FGFRs play an important role for the progression of the disease. It works by blocking the FGFRs' signaling cascades inside the cell (Figure 1). Given that an abnormal, overactive FGFR3 is the cause of achondroplasia, investigators sought to find whether infigratinib could be used to treat this skeletal dysplasia. Preclinical studies demonstrated that it rescued bone growth in a mouse model of achondroplasia, in doses much lower than those used in the first studies in cancer (12,13).

QED, a BridgeBio arm, has been conducting the phase 2 trial called PROPEL and, according to their presentation during the JPMorgan 2022 Healthcare Conference, infigratinib has been showing a safe profile. They estimate to have results from the study by the end of the second quarter this year (Figure 3). Depending on the results they plan to open the phase 3 study right in 2023.

Figure 3. Phase 2 study PROPEL design (from the BridgeBio’s JPMorgan 2022 Healthcare Conference presentation).








Recifercept

Recifercept is a modified, free form of FGFR3 that works as a "ligand trap", capturing FGFR activators (ligands: the FGFs) before they can bind and activate these receptors, including FGFR3. Without the activators FGFR3 would not be as active as expected and this would help restoring bone growth (14,15).

Pfizer has started a phase 2 study with recifercept in the end of 2020 but there have been no significant updates since then. 

Meclizine

Drug repurposing is a strategy where investigators try to find new therapeutic indications for old drugs. The concept is that its development for the new purpose should be much less expensive and the final drug cost, if approved, would be surely more affordable than the cost of newly created compounds. Meclizine is an old drug that has been used to treat motion sickness for decades. In an effort to find potential treatments for achondroplasia the Japanese group from University of Nagoya leaded by Dr. Kitoh has found that meclizine was able to inhibit the FGFR3 function and to partially rescue bone growth in their animal model (10,16). They have subsequently conducted a phase 1 study in children with achondroplasia (17). The study showed that meclizine could be suitable for a single daily dose (but that it would need to be further explored in subsequent studies). More recently, they conducted another study to evaluate multiple doses of meclizine for a period of two weeks, but no results have been published yet.



RBM-007

Ribomic has been developing RBM-007, an anti-FGF2 aptamer designed to treat conditions where FGF2 has a relevant role in the mechanism of disease (18). Since FGF2 is considered a key activator (ligand) of FGFR3 and that in achondroplasia FGFR3 is overactive, then if it was less activated by FGF2 perhaps bone growth could be restored.

Ribomic published their pre-clinical studies with RBM-007, which indeed rescued bone growth in a model of achondroplasia (19). They have already started a phase 1 clinical trial to evaluate this aptamer for achondroplasia and are planning to start a phase 2 study in children with achondroplasia during 2022 (Figure 4).

Figure 4. Clinical development plan of RBM-007 for achondroplasia (from Ribomic’s JPMorgan 2022 Healthcare Conference presentation).







SAR442501

Last year, Sanofi announced that SAR442501, an anti-FGFR3 antibody, was transitioned to Phase 1 clinical development. However, no study information could be found on the European Clinical Trial Register, on ClinicalTrials.gov, or the Australian Clinical Trial Register. Apart from being listed in the Sanofi’s pipeline website and in their Feb 2021 financial report (and other reports in their website), no further information about the development of SAR442501 could be found there. Neither pre-clinical data could be found in the Pubmed portal nor through a Google search as of 31-Jan-2022.

Although the antibody strategy is attractive due to its high specificity, the ability of a specific antibody to target FGFR3 in the growth plate in a model of achondroplasia needs to be confirmed in an appropriate model. As mentioned above, the growth plate is a unique body tissue because it lacks direct blood supply. Nutrients and oxygen must traffic through a dense matrix which involves the chondrocytes. In this setting, large molecules such as antibodies might not be able to reach out to chondrocytes to exert their effects (20).

SAR442501 is not the first antibody against FGFR3 to be developed (6). Until recently, B-701 (R3Mab) (21), also known as votafamab, was being developed for cancer and potentially for achondroplasia, but it seems that the research for this indication has been abandoned as there have been no reports about this antibody for this indication for a long time. 

ASP-5878

Astellas Pharma has recently published a study where they explored the use of ASP-5878, a TKI similar to infigratinib, in pre-clinical models to treat achondroplasia (22). They found that the drug was able to improve bone growth, however it was less effective compared to a positive control, a CNP analog bearing the same structure of vosoritide. 

ASB-20123

Asubio, a Japanese biotech that was recently incorporated by Daichii-Sankio (DS), was developing another CNP analog based on the fusion of the active fragment of CNP and a backbone fragment of the hormone ghrelin to help extending the known short CNP’s half-life. They have published some studies showing that their molecule was able to improve bone growth in pre-clinical models (23) but there has been no news about this compound in the DS website or in the literature lately.


A new era started

With the approval of vosoritide, a new era started. Treating achondroplasia goes far beyond simply improving the final individual height, which nevertheless is an important objective. Although long term data about the effects of vosoritide (and of course the others, too) is not available yet, based on current evidence, there is a fair chance that these therapies may mitigate or prevent several clinical challenges children with achondroplasia face in their daily routine, as mentioned in the beginning of this review.

These children now may have access to a therapy that might help them develop better and have the same opportunities and challenges an average child has while they grow into adulthood. Neither more nor less. I think this is a good perspective. 

References

1. Horton WA et al. Achondroplasia. Lancet 2007; 370: 162–72.

2. Toydemir RM et al. A novel mutation in FGFR3 causes camptodactyly, tall stature, and hearing loss (CATSHL) syndrome. Am J Hum Genet 2006;79(5):935-41. Open access.

3. Savarirayan R et al. International Consensus Statement on the diagnosis, multidisciplinary management and lifelong care of individuals with achondroplasia. Nat Rev Endocrinol 2021 Nov 26. Open access.

4. Hoover-Fong J et al. Lifetime impact of achondroplasia: Current evidence and perspectives on the natural history. Bone. 2021 May;146:115872. Open access.

5. Aviezer D et al. Fibroblast growth factor receptor-3 as a therapeutic target for Achondroplasia--genetic short limbed dwarfism. Curr Drug Targets 2003 Jul;4(5):353-65.

6. Golembo M and Yayon A. Method and composition for treatment of skeletal dysplasias. US patent 20040138134. September 2003. Open access.

7. Yasoda A, Nakao K. Translational research of C-type natriuretic peptide (CNP) into skeletal dysplasias. Endocr J 2010;57(8):659-66. Open access.

8. Lorget F et al. Evaluation of the therapeutic potential of a CNP analog in a Fgfr3 mouse model recapitulating achondroplasia. Am J Hum Genet 2012 Dec 7;91(6):1108-14. Open access.

9. Breinholt VM et al. TransCon CNP, a Sustained-Release C-Type Natriuretic Peptide Prodrug, a Potentially Safe and Efficacious New Therapeutic Modality for the Treatment of Comorbidities Associated with Fibroblast Growth Factor Receptor 3-Related Skeletal Dysplasias. J Pharmacol Exp Ther 2019; 370(3): 459-71. Open access.

10. Matsushita M et al. Meclozine facilitates proliferation and differentiation of chondrocytes by attenuating abnormally activated FGFR3 signaling in achondroplasia. PLoS One 2013 Dec 4;8(12): e81569. doi: 10.1371/journal.pone.0081569. Open access.

11. Savarirayan R et al. Once-daily, subcutaneous vosoritide therapy in children with achondroplasia: a randomised, double-blind, phase 3, placebo-controlled, multicentre trial. Lancet 2020; 396 (10257):1070.

12. Komla-Ebri D et al. Tyrosine kinase inhibitor NVP-BGJ398 functionally improves FGFR3-related dwarfism in mouse model. J Clin Invest 2016; 126(5):1871-84. Open access.

13. Demuynck B et al. Support for a new therapeutic approach of using a low-dose FGFR tyrosine kinase inhibitor (infigratinib) for achondroplasia. Approved by but not presented at ENDO 2020 due to COVID-19 pandemics. Accessed on 01-Jan-2022. Open access.

14. Garcia S et al. Postnatal soluble FGFR3 therapy rescues achondroplasia symptoms and restores bone growth in mice. Sci Transl Med 2013; 5 (203):203ra124. Open access after registration.

15. Gonçalves D et al. In vitro and in vivo characterization of Recifercept, a soluble fibroblast growth factor receptor 3, as treatment for achondroplasia. PLoS ONE 2020; 15(12): e0244368. Open access.

16. Matsushita M et al. Meclozine promotes longitudinal skeletal growth in transgenic mice with achondroplasia carrying a gain-of-function mutation in the FGFR3 gene. Endocrinology 2015; 156(2):548-54. Open access.

17. Kitoh H et al. Pharmacokinetics and safety after once and twice a day doses of meclizine hydrochloride administered to children with achondroplasia. PLoS ONE 2020;15(4): e0229639. Open access.

18. Ling Jin et al. Dual Therapeutic Action of a Neutralizing Anti-FGF2 Aptamer in Bone Disease and Bone Cancer Pain. Mol Ther 2016; 24 (11): 1974-1986. Open access.

19. Kimura T et al. An RNA aptamer restores defective bone growth in FGFR3-related skeletal dysplasia in mice. Sci Transl Med 2021 May 5;13(592): eaba4226.

20. Farnum CE et al. In vivo delivery of fluoresceinated dextrans to the murine growth plate: imaging of three vascular routes by multiphoton microscopy. Anat Rec A Discov Mol Cell Evol Biol 2006 Jan;288(1):91-103. Open access.

21. Qing J et al. Antibody-based targeting of FGFR3 in bladder carcinoma and t(4;14)-positive multiple myeloma in mice. J Clin Invest 2009 May;119(5):1216-29. Open access.

22. Ozaki T et al. Evaluation of FGFR inhibitor ASP5878 as a drug candidate for achondroplasia. Sci Rep 2020; 10: 20915. Open access.

23. Morozumi N et al. ASB20123: A novel C-type natriuretic peptide derivative for treatment of growth failure and dwarfism. PLoSONE 2019;14(2): e0212680. Open access.

Treating achondroplasia: from dream to reality

The future is at our door

We are now less than two weeks from Voxzogo's PDUFA* date, the day when the Food and Drug Administration (FDA) will release its response to vosoritide's application for commercialization. Vosoritide has been under clinical development for about ten years now, being investigated as a therapy for achondroplasia, the most common form of dwarfism. This long run has been taken with several humps and bumps throughout the way and, now that the drug is already approved in Europe, the expectations are all on how, and if, the decision by the FDA will truly open new doors for families interested in improving the health of their affected children. But let's see what these expectations are all about since the next steps may come with surprises.

As the 17 readers of this blog certainly know, achondroplasia is caused by a mutation on the gene that encodes an enzyme called fibroblast growth factor receptor 3 (FGFR3). I know, I know, I might become a little bit repetitive, but I think that the circle I will be doing here might help us to understand what we may expect on that vosoritide's breakthrough date (PDUFA). 

Causes and consequences

FGFR3, along with many other enzymes, plays a fundamental role during the phase scientists call development. Development starts with the fertilized egg and goes up until the end of puberty, and it is comprised by biological processes tightly regulated by hundreds of enzymes like FGFR3. You could call these processes standard operating procedures (SOPs). These enzymes work in concert to make the SOPs to run smoothly, but when one of them is modified (mutated) either working more than planned or not working at all, then the development process is deranged. 

FGFR3 is particularly important in bone development because it works by reducing the pace of bone growth, modulating the growth stimuli produced by several other enzymes. In a car, while those other enzymes would work as an accelerator, FGFR3 is a brake. If there was no FGFR3, bones would grow without control and cause several medical problems. In fact, mutations in FGFR3 that inactivate it do cause an overgrowth syndrome known as CATSHL syndrome  (camptodactyly, tall stature, scoliosis and hearing loss) (1).

A brake is important in a car, so its speed can be controlled. However, the mutation in FGFR3 that causes achondroplasia makes it to work too much, so the car can barely move (the brake rules over the accelerator). The result is that, in achondroplasia, bones, and especially the long bones and vertebrae, grow just a fraction of what they were supposed to, in contrast with all other body tissues. Individuals with achondroplasia have short adult stature but this is not the only key characteristic since restricted skeletal growth has consequences beyond height. 

The imbalance between shorter or narrow bones compared to all the other normal tissues will frequently lead to clinical complications that are listed in the published guidelines about achondroplasia. Due to their bone growth impairment, on average individuals with achondroplasia require more healthcare utilization, including surgical treatment to common orthopedic and neurological complications (e.g.: foramen magnum stenosis, spinal stenosis, joint problems, etc.) among others, while adults are also prone to obesity, higher incidence of cardiac disorders and have a shorter life span compared to the general population. (2)

As the knowledge about the natural history of achondroplasia improves it becomes clear that it is a genetic disorder affecting much more than the final height. 

Developing the first therapy for achondroplasia

The gene alteration that leads to achondroplasia was identified almost 30 years ago (3-5), but only more recently efforts have been directed to find ways to correct the bone growth defect caused by the overactive FGFR3 mutation. This became possible because the chemical networks regulated by FGFR3 have been identified (Figure 1) as well as of most of those pathways driven by the other agents involved in bone development and growth. This in turn allowed scientists to find out which of those pathways were impacted by mutations in FGFR3. (6)

Figure 1. FGFR3 relevant pathways in the chondrocyte.

One of those other bone development agents is an enzyme called natriuretic peptide receptor B (NPR-B). Both FGFR3 and NPR-B are located in the cell membrane of the chondrocytes, the cells that govern bone growth. They can be seen as power switches in our home walls that are turned on and off when we move them up and down. In the body, FGFR3 is turned on by FGFs while NPR-B is activated by the C-type natriuretic peptide (CNP). Scientists have discovered that CNP is a positive bone growth agent that works precisely reducing the activity of FGFR3 in the chondrocyte. (Figure 2). They have also seen that the FGFR3 pathway may downregulate the CNP+NPR-B axis. (7)

Figure 2. Crosstalk of FGFR3 and CNP pathways in the chondrocyte.

 

Having learned that CNP modulates FGFR3 activity and that it was working less than normal in achondroplasia, it was natural to check out if providing supplemental CNP would help reducing the effects of the mutated FGFR3. In fact, this was readily seen: adding CNP to cell cultures, bone explants and animal models of achondroplasia restored, at least partially, bone growth. (8) A first potential therapy for achondroplasia was at hand.

However, one problem that scientists faced when dealing with CNP is that this is a fragile molecule. Peptides like CNP are very active and must stay under control. When in the blood CNP will last less than three minutes circulating as it is an easy target for natural clearing systems we have. So, how to solve this problem? They learned that another natriuretic peptide called BNP is naturally more resistant to the clearing system due to having a slightly different structure. They adapted CNP to "look like" BNP and this change rendered the invention of vosoritide. (9) Therefore, vosoritide is a modified version of CNP, also called an analogue.

Vosoritide lasts about 20 minutes in the blood, enough time to reach the bone growth zones (the growth plates) and to exert its effects. So, what are these effects ? By reducing FGFR3 activity the NPR-B axis restores the chondrocyte capability to proliferate and enlarge (hypertrophy), which are the two key steps they need to take to make the bones grow. (8)

One hard challenge in the beginning of the clinical development of vosoritide must have been how to measure its efficacy. In humans, bone growth constitutes a long and slow process so changes are not identified in a day-to-day basis, but can only be seen when two distant time points are compared. This slow development makes it difficult to set objectives when someone is trying to correct a derangement in the bone growth process. Even harder would be to confirm whether the improved bone growth under the experimental drug would provide additional benefits in terms of reducing the frequent medical complications that result from the short and narrow bones, such as spinal stenosis. So, how can we measure those effects? After long discussions, as we can see described in the many public calls (mostly those financial conferences) throughout the years, the agreed endpoint between the developer and regulators that would allow determining if vosoritide was beneficial (efficacy) in the treatment of achondroplasia was bone growth velocity.

Vosoritide has been under tests in children with achondroplasia for years now and, according to the data already available, it helps to restore bone growth to an extent that is close to what happens in an average child. (10-12) The data that have been submitted to the European Medicines Agency (EMA) have been analyzed and, in last August, vosoritide was approved for the treatment of achondroplasia in the European countries that work with that agency. The same data have also been submitted to the Food and Drug Administration (FDA) which will be delivering their feedback in a few days more, as I mentioned above.

The future is present

The approval of vosoritide in Europe is a landmark for the treatment of achondroplasia and very likely to many other skeletal dysplasias where bone growth is impaired. One important characteristic of the CNP+NPR-B axis is that it works independently of FGFR3. The use of CNP analogues like vosoritide (there are others in development) may help improve bone growth in those other genetic disorders, thus not only improving height, but also medical complications related to other restricted growth conditions, as we expect to see in achondroplasia.

It may take a few years more to see whether children being treated with vosoritide will suffer fewer complications such as middle ear infections, sleep apnea, spinal stenosis, genu varum, etc. than what is frequently seen today, but the long term expectations about these potential benefits should not drive any conclusion that this drug, and all the other candidates to come, would not help to reduce those complications. 

And why is that so? Simply because the treatment is systemic, meaning that the drug reaches all bones at the same time. There is no logic in thinking that only one type of bone would be affected by the treatment. Therefore, the treatment not only should increase the length of long bones but also should help widening other bones such as the vertebrae, which grow through growth plates, too.

Children's health

Here is the World Health Organization definition of health:

• Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.

The accumulating evidence about the natural history of achondroplasia shows that both children and adults with this skeletal dysplasia endure impacts not only on the physical aspect but both in the mental (emotional) and social well being fields, too.(13,14) It will be good to see how the upcoming pharmacological treatments for achondroplasia will affect these aspects of health. Based on published evidence, individuals submitted to limb lengthening have improved quality-of-life after the surgery (15, 16), implying that the improved height was beneficial on those other aspects of health highlighted in the WHO definition. Someone pondering about this improvement seen after lengthening surgery needs to recall that the surgery only increases height, not having any effect in other characteristics of achondroplasia and its common complications, in contrast with what is expected with pharmacological therapies.  

We can foresee a time when babies and toddlers with achondroplasia won't need MRIs to rule out foramen magnum stenosis, or children attending repeated visits to a ENT specialist to insert ear tubes, or undergo amigdalectomy to improve their sleep apnea, just to cite a few of the stressful situations they frequently endure early in life. They might also be able to do anything an average child does, without common challenges they face today due to their restricted growth.

In conclusion, based on the current evidence, I believe that with improved bone growth, children with achondroplasia under treatment with vosoritide, and in the future with other potential therapies, will achieve benefits that go beyond the reduction of the risk of medical complications but also to improvement in mental and social aspects as well. These potential benefits must be kept in mind by stakeholders that will be in charge to decide whether to adopt therapies for achondroplasia or not. For me, the simple answer is yes.

References

* From Wikipedia: PDUFA date: In United States pharmaceutical regulatory practice, the PDUFA date is the colloquial name for the date by which the Food and Drug Administration must respond to a New Drug Application or a Biologics License Application.

1. Toydemir RM, Brassington AE,  Bayrak-Toydemir P et al. Novel mutation in FGFR3 causes Camptodactyly, Tall Stature, and Hearing Loss (CATSHL) Syndrome. AGHG 2006; 79 (5): 935-41. Free access.

2. Hoover-Fong J, Scott CI, Jones MC et al. Health supervision for people with achondroplasia. Pediatrics 2020 Jun;145(6):e20201010. Free access.

3. Rousseau F, Bonaventure J, Legeai-Mallet L et al., Mutations in the gene encoding fibroblast growth factor receptor-3 in achondroplasia. Nature 1994; 371 (6494); 252–54. Free access.

4. Shiang R, Thompson LM, Zhu YZ et al. Mutations in the transmembrane domain of FGFR3 cause the most common genetic form of dwarfism, achondroplasia. Cell 1994;78 (2): 335–42.

5. Bellus GA, Hefferon TW, Ortiz de Luna R et al. Achondroplasia is defined by recurrent G380R
mutations of FGFR3. Am J Hum Genet 1995; 56:368-73. Free access.

6. Legeai-Mallet L and Savarirayan R. Novel therapeutic approaches for the treatment of achondroplasia. Bone 2020; 141:115579. Free access.

7. Ozasa A, Y. Komatsu A. Yasoda M et al. Complementary antagonistic actions between C-type natriuretic peptide and the MAPK pathway through FGFR-3 in ATDC5 cells. Bone 2005; 36: 1056-64. Free access.

8. Lorget F, Kaci N, Peng J et al. Evaluation of the therapeutic potential of a CNP analog in a Fgfr3 mouse model recapitulating achondroplasia Am J Med Gen 2012; 91(6):1108-14. Free access.

9. Wendt DJ, Dvorak-Ewell M, Bullens S et al. Neutral endopeptidase-resistant C-type natriuretic peptide variant represents a new therapeutic approach for treatment of fibroblast growth factor receptor 3-related dwarfism. J Pharmacol Exp Ther 2015;353(1):132-49.

10. Savarirayan R, Irving M, Bacino CA et al. C-Type Natriuretic Peptide Analogue Therapy in Children with Achondroplasia. N Engl J Med 2019; 381(1):25-35. Free access.

 

11. Savarirayan R, Tofts L, Irving M. Once-daily, subcutaneous vosoritide therapy in children with achondroplasia: a randomised, double-blind, phase 3, placebo-controlled, multicentre trial. Lancet 2020; 396(10252):684-692. Free access.

12.  Savarirayan R, Tofts L, Irving M. Safe and persistent growth-promoting effects of vosoritide in children with achondroplasia: 2-year results from an open-label, phase 3 extension study. Genet Med 2021 Aug 2;1-5. doi: 10.1038/s41436-021-01287-7. Free access.

13. Witt S, Kolb B, Bloemeke J et al. Quality of life of children with achondroplasia and their parents - a German cross-sectional study. Orphan J Rare Dis 2019;14(1):194. Free access. 

14. Yonko EA, Emanuel JS, Carter EM et al. Quality of life in adults with achondroplasia in the United States. Am J Med Gen 2021; 185(3):695-701.

15. Moraal JM, Elzinga-Plomp A, Jongmans MA et al. Long-term psychosocial functioning after Ilizarov limb lengthening during childhood, Acta Orthopaedica 2009; 80 (6): 704-10. Long-term psychosocial functioning after Ilizarov limb lengthening during childhood: 37 patients followed for 2–14 years. Free access.

16. Kim, SJ., Balce, G.C., Agashe, M.V. et al. Is Bilateral Lower Limb Lengthening Appropriate for Achondroplasia?: Midterm Analysis of the Complications and Quality of Life. Clin Orthop Relat Res 2012; 470: 616–21. Free access.

Treating achondroplasia: vosoritide approved in Europe for the treatment of achondroplasia

This is a major breakthrough. The European Medicines Agency (EMA) has just released their decision to approve Voxzogo (vosoritide) for the treatment of achondroplasia in children two year-old and older until their growth plates close.

EMA approval decision.

This approval comes not far behind the recent decision by the French health authority to grant temporary approval for vosoritide in children 5+ years of age in July. You can read the French authorization and prescription protocol here (in French).

You can read the Biomarin's press release here. 

Great news for so many children in the world!

Treating achondroplasia: nine years online

 The blog "Treating achondroplasia" turned nine years old this year. When I started to write the articles for the blog the landscape was completely different: there was really nothing in the horizon towards therapeutic strategies for achondroplasia. Individuals with achondroplasia could only - and, as matter of fact, this is still true today - rely on surgical procedures to correct or improve skeletal problems which come with the typical bone growth impairment caused by the overactive fibroblast growth factor receptor 3 (FGFR3) mutation. Infants with foramen magnum stenosis, children with bowed legs, teens and adults with spinal stenosis sometimes must undergo several surgical interventions to control these and other common neurological and orthopedic complications seen in achondroplasia.

However, things are changing. There are now several potential pharmacological therapies in several stages of development as you can see in the last article published in January in the blog. One of them, vosoritide, is in the last sprint towards approval by two of the most important world regulatory agencies, the European Medicines Agency (EMA) and the Food and Drug Administration (FDA). Others still have to prove their safety and efficacy in clinical trials and most of them should reach the stage where vosoritide is now. If vosoritide data provided by the developer to EMA and FDA is sound and reliable it is expected that it will be approved and made available next year. This will become a turning point. 

Achondroplasia is a genetic disorder of bone development, meaning that the effects of the mutation in FGFR3 are restricted to the life interval when bones grow. FGFR3 is a natural inhibitor of the bone growth process and, because of the mutation, in achondroplasia it is working too much leading to growth arrest.The end of puberty also represents the end of the bone development process. Unfortunately, because of this, adult individuals would have no benefits in receiving a therapy against FGFR3, at least with the intent of achieving bone growth.

Therapies for achondroplasia will benefit children and teenagers and it is expected that the earlier they start a therapy the better would be the outcomes, although this expectation still needs to be confirmed with data coming from the studies in younger children currently ongoing. 

Why is important to start the therapy early?  Because it is during the first two years of life (and specially during the first year) that children experiment their highest growth velocity rate. Of course, achondroplasia is already identifiable before birth but it is unlikely that a pharmacological intervention so early in life will be available soon. It is during the first two years of life that most of the clinical features of achondroplasia will be established so, if a therapy can be initiated early, it might more efficiently reduce or mitigate those features, which in turn might prevent the common complications I mentioned above.

The Treating Achondroplasia blog is active and I will keep publishing updates as relevant information is released. I really hope that the blog is helping the interested reader to better understand achondroplasia, FGFR3 and what to expect with the new therapies. See you soon. ;)