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Achondroplasia

Background

Achondroplasia is a rare genetic condition that causes reduced bone formation at the 'growth plate' (a section of cartilage at either end of the bone, responsible for growth). This results in shortened limbs. Those affected usually have a normal life expectancy and range of intelligence.

Credits

Last updated February 2017 by Dr W Christian, Consultant Paediatrician, Bristol Royal Hospital for Children, Bristol, UK.

Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information is provided is for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

What are the symptoms?

People with achondroplasia have a range of characteristics, including:

  • a near normal trunk length with shorter arms and legs
  • a large head with prominent forehead and flattened bridge of the nose
  • an increased curvature of the lower spine (lumbar lordosis)
  • bowing of the lower legs
  • crowded teeth, in some cases
  • short, broad feet and hands with separation between middle and ring fingers (known as the 'trident' hand)
  • flexible joints.

Babies with achondroplasia may develop their motor skills (the ability to use and co-ordinate the muscles in their body) and mobility more slowly than normal because of the combination of a heavier head and shorter arms and legs, but ultimately their development should be within the expected normal range.

What are the causes?

Achondroplasia is due to a change, called a mutation, in the gene that codes for fibroblast growth factor receptor 3 (FGFR3), an important component of bone development. This leads to FGFR3 being activated resulting in restricted bone growth. In almost all cases, the change in the DNA which makes up the gene occurs at exactly the same point each time making it relatively straightforward to detect.

How is it diagnosed?

Diagnosis will be based on the presence of typical clinical features. X-rays may be needed to demonstrate changes in the skeleton that confirm the presence of the condition. Molecular testing (testing DNA) of those affected can confirm if the mutation in FGFR3, and therefore the condition, is present.

How is it treated?

There is no cure for achondroplasia, but many of the problems associated with the condition can be detected and addressed through regular health checks involving a multidisciplinary team of health professionals including the general practitioner (GP). Growth charts designed specifically for children with achondroplasia should be used to monitor weight, length and head growth.

Children should see a paediatrician regularly who will be able to keep an eye on development and advise on lifestyle changes, such as a good diet and regular exercise. Surgery may be required to aid with spinal curvature and leg bowing. Regular assessment by a community dentist may be required to assess any dental problems.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
Most people with achondroplasia are born to average size parents where the change in the FGFR3 gene has occurred for the first time prior to conception (sporadic mutation). For parents with achondroplasia the inheritance pattern is autosomal dominant.

Prenatal diagnosis
Ultrasound scans may detect disproportionately short limbs at around 25 weeks of pregnancy. For couples where one or both already has the condition, a chorionic villus sampling test or amniocentesis may be available to look for the change in the FGFR3 gene.

Is there support?

Information and support in the UK for achondroplasia is provided by the Restricted Growth Association (see entry Restricted Growth).

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