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Achondroplasia Definition

What is it Achondroplasia  ?

Achondroplasia done is a particular type of chondrodyplasia, either is a form of narrowing and / or elongation of the limbs. This disease is characterized by:

  • Rhizomelia: which reaches the root of the limbs, the thigh or the arms;
  • Hyper-lordosis: accentuation of the dorsal curves;
  • Brachydactyly: abnormally small size of the phalanges of the fingers and / or toes;
  • Macrocephaly: abnormally large size of the cranial perimeter;
  • hypoplasia: delayed growth of tissue and / or organ.

Ethnologically, achondroplasia refers to “without the formation of cartilage”. This cartilage is a hard but flexible tissue that is part of the skeletal composition. Nevertheless, in this pathology, it is not a malformation in the cartilage but a problem in the ossification (formation of the bones). This applies more to long bones, such as arms and legs.

The subjects affected by achondroplasia show a small build. The average size of a man with achondroplasia is 1.31 m and that of a sick woman, 1.24 m.

The particular characteristics of the disease are reflected in a large trunk size, but an abnormally small size of the arms and legs. In contrast, macrocephaly is generally associated, which is defined by an enlargement of the cranial perimeter, especially of the forehead. The fingers of these patients are usually small with a visible divergence of the major, which gives a trident hand shape.

Some health problems may be associated with achondroplasia. This is particularly the case of respiratory abnormalities with a breath that is slowed down by blows with periods in apnea. In addition, obesity and infections in the ears are often associated with the disease. Posture problems are also visible (hyper-lordosis).

Potential complications may appear, such as a spinal stenosis, or narrowing of the medullary canal. This results in compression of the spinal cord. These complications are usually signs of pain, weakness in the legs and tingling.

At a lower frequency, the appearance of hydrocephalus (severe neurological abnormality) is possible. (2)

It is a rare disease whose prevalence (number of cases in a given population at a given time) is 1 birth out of 15,000. (2)

Symptoms of Achondroplasia

Clinical manifestations of achondroplasia result in birth:

  • – abnormally small limb size with rhizomelia (limb root involvement);
  • – an abnormally large trunk size;
  • – an abnormally large size of the cranial perimeter: macrocephaly;

Hypoplasia : delayed growth of tissue and / or organ.

A retardation of the motricity is also significant of the pathology.

Other consequences may include sleep apnea, recurrent otitis, hearing disorders, dental overlap, thoraco-lumbar kyphosis (spinal deformity).

In the most severe cases of the disease, spinal cord compression can be related to it, causing apnea, developmental delay and pyramidal signs (all of the motor disorders). In addition, hydrocephalus is also plausible leading to neurological deficits and cardiovascular disease.

Individuals with the disease have an average size of 1.31 m for men and 1.24 m for women.

Moreover, obesity is largely found in these patients.

The origins of the disease

The origin of achondroplasia is genetic.

Indeed, the development of this disease results from mutations within the FGFR3 gene. This gene allows the formation of the protein involved in the development and regulation of bone and cerebral tissues.

There are two specific mutations in this gene. According to scientists, these mutations cause too much activation of the protein, interfering with the development of the skeleton and causing bone deformations.

Transmission of the disease occurs from an autosomal dominant process. Either only one of the two copies of the mutated gene of interest is sufficient for the subject to develop the associated diseased phenotype. Patients with achondroplasia then inherit a copy of the mutated FGFR3 gene from one of the two sick relatives.

By this mode of transmission, there is therefore a 50% risk of transmitting the disease to the offspring.

Subjects inheriting the two mutated copies of the gene of interest develop a severe form of the disease causing significant limb and bone contraction. These patients are usually born prematurely and die shortly after the onset of respiratory failure.

Risk Factors

The risk factors for the disease are genetic.

Indeed, the transmission of the disease is via an autosomal dominant transfer relative to the gene FGFR3.

This transmission principle reflects that the unique presence of a single copy of the mutated gene is sufficient in the development of the disease.

In this sense, an individual possessing one of his two parents suffers from this pathology, has a 50% risk of inheriting the mutated gene, and thus also develop the disease.

Prevention and Treatment

The diagnosis of the disease is first of all differential. Indeed in view of the various associated physical characteristics: rhizomelia, hyper-lordosis, brachydactyly, macrocephaly, hypoplasia, etc. the doctor can assume the disease in the subject.

Associated with this first diagnosis, genetic tests make it possible to demonstrate the possible presence of the mutated FGFR3 gene.

Treatment of the disease is first and foremost a consequent prevention. This prevents the development of complications, which may be lethal, in patients with achondroplasia.

Hydrocephalus surgery is often required in newborns. In addition, other surgical procedures can be performed to lengthen the limbs.

Ear infections, ear infections, hearing problems, etc. are treated with suitable medicines.

The prescription of speech therapy courses may be useful for some sick subjects.

Adenotonsillectomy (ablation of tonsils and vegetations) can be performed in the treatment of sleep apnea.

Added to these treatments and surgical procedures, nutritional monitoring and diet are generally advised in sick children.

The life expectancy of patients is slightly lower than the life expectancy of the general population. Moreover, the development of complications, especially cardiovascular, can have negative consequences on the life expectancy of patients.

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