Hypochondroplasia (HCH) is one of the skeletal dysplasias, which cause short stature due to reduced bone growth. In HCH, there is shortening mainly of the limbs. The condition affects males and females equally. There are a number of people with HCH who are not aware that they have the condition since the limb shortening can be mild and there may be no other features. As a result, the incidence of HCH is uncertain. It is thought that its incidence could be between 1 in 15,000 to 1 in 40,000 live births.
Medical text written September 2004 by Contact a Family. Approved September 2004 by Dr M Wright. Last updated by October 2010 by Dr M Wright, Consultant Clinical Geneticist, Northern Genetics Service, Newcastle upon Tyne Hospitals, Newcastle upon Tyne, UK.
The features of HCH may include:
- short stature with an adult height in the range of 128 to 151 cm (4 feet 2 inches to 4 feet 11 inches)
- disproportionate shortening of the arms and legs with short, broad hands and feet
- macrocephaly (large head)
- limitation of elbow extension with increased mobility in other joints
- increased lumbar lordosis (exaggerated curvature at the lower end of the spine)
- joint pain due to abnormal alignment of bones and joints
- mild learning problems – this appears to be a feature in a proportion of people with HCH.
About 70 per cent of people with HCH have a change in the FGFR3 gene on chromosome 4. Changes in this gene also cause achondroplasia. The remaining 30 per cent of those with HCH will either have a so far unrecognised change in the FGFR3 gene or a change in other as yet unidentified genes.
It is not easy to diagnose HCH in very young children and may even be difficult in adults. Diagnosis is made by identifying the features known to appear in HCH together with radiological (X-ray) findings. DNA-based testing may confirm the presence of a change in the FGFR3 gene. The absence of a gene change however does not rule out HCH.
There is no treatment for the underlying cause of HCH. Surgery may be necessary to correct bowing of the legs if this causes symptoms. Physiotherapy may also be helpful if there is joint pain. Surgical limb lengthening can be considered but it is a prolonged process requiring a number of operations. Human growth hormone therapy has been given to some children with HCH, but has not been shown to significantly increase final adult height.
Support is available for children with HCH and their families from a number of organisations. Aids may be required to improve access and to facilitate the use of household, school and workplace equipment.
HCH is inherited in an autosomal dominant manner. The parents of most children with HCH do not have the condition. The gene change which causes HCH seems to occur frequently as a new event (a sporadic mutation). A person with HCH has a 50 per cent chance of having a child with the condition.
Chorionic villus sampling or amniocentesis is available if a parent has HCH and a mutation in the FGFR3 gene has been identified. Where the mutation has not been identified, ultrasound scanning is the only method of prenatal testing. Families where HCH has been diagnosed should seek genetic counselling.
Information and support in the UK for hypochondroplasia is provided by the Restricted Growth Association (see entry Restricted Growth).