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Achondroplasia

Name of disease:

Achondroplasia

ICD-10 diagnosis code:

Q77.4

Causes:

Achondroplasia is a rare genetic disorder in which endophytic bone formation is impaired due to the gain-of-function mutation of the fibroblast growth factor receptor-3 (FGFR3) gene, which in turn affects the height and other complications.

Mode of inheritance:

The inheritance pattern of this disease is autosomal dominant, that is, if either parent has a disease-causing gene variant, they will give birth to a child with a 50% chance of inheriting the disease-causing gene variant.
About 75% to 80% of patients are born to parents of normal height, indicating that this is a new dominant mutation.

Prevalence:

1/26,000 – 40,000

Diagnosis:

The diagnosis of osteogenesis imperfecta is based on the patient's symptoms, which are mainly based on a combination of clinical and radiological features。
If the doctor is unsure about the diagnosis of the patient, molecular genetic testing can be used to determine whether the patient carry the FGFR3 mutation.

Age of onset:

It begins in the developing fetus.

Common signs and symptoms:

Short stature
Unusually large head with a prominent and flat nasal bridge
Short arms and legs. Prominent abdomen and buttocks.
Short fingers and toes with trident hands
Lordosis or kyphosis
Redundant skinfolds in upper extremities
Developmental delay
Sleep apnea

Available treatments (medicinal and non-medicinal):

At present, the drugs approved by drug therapy in the European Union and United States are CNP (C-type natriuretic peptide) drugs, which are transformed into signals to enhance the growth of cartilage ossification and reduce the negative regulation of FGFR3.
Other treatments mainly help to alleviate the symptoms, For example, physiotherapy is recommended for children with developmental delay.

Disease management tips:

Treating achondroplasia requires a multidisciplinary approach to the specific symptoms of the patient. Multidisciplinary management recommendations cover every stage from birth to adulthood, emphasizing the importance of early diagnosis, genetic counselling, and a continued focus on the patient's physical and mental health.
In the neonatal and infant stages, emphasis is placed on confirming the diagnosis and providing family support. Professionals such as paediatricians, geneticists, dietitians, and physiotherapists will be involved in the care of patients．
Evaluation of the craniocervical junction is an important part of the infant and toddler stages, with neuroimaging by CT or MR and polysomnography of sleep shortly after birth to confirm complications such as sleep apnea.
As patients enter preschool and school age, the development of educational support and social skills becomes critical. This may require the involvement of special education specialists, psychologists, and social workers.
As adults, care for patients will shift to vocational training, employment support, and possibly family planning. The help of occupational therapists and counsellors may be required at this stage.
Short limbs may affect the patients’ self-care abilities in daily situations, such as eating, bathing, or dressing. Therefore, in daily life, they may need special arrangements, such as using lower chairs and tables, as well as using stools when going to the toilet.
The patient's height and head circumference should be regularly recorded on relevant growth charts to monitor growth progress and avoid unnecessary imaging. However, growth hormone therapy is not recommended as it can cause disproportionate body shape.
Similarly, patients are not advised to use vertical swing because patients have larger heads and the swings can force the head in hyperflexion position, which leads to cord compression.
For pregnant women with achondroplasia, cesarean section is recommended for delivery because of the small pelvic size.

References:

https://rarediseases.org/rare-diseases/achondroplasia/ https://medlineplus.gov/genetics/condition/achondroplasia/ https://pubmed.ncbi.nlm.nih.gov/34837063/

Other useful websites:

More about the disease: https://www.healthline.com/health/achondroplasia#genetic-factors Patient groups: Little People of Hong Konghttps://www.lphk.org Little People of Americahttps://www.lpaonline.org