Hypochondroplasia is a rare inherited skeletal dysplasia (condition of abnormal bone growth or development) causing short stature due to short limbs. HCH affects both males and females. Where the only feature in an individual is short stature, medical intervention may not be sought. As a result, the incidence of HCH is uncertain. It is thought that its incidence could be 1:15,000 to 1:40,000 live births.

About 70 per cent of people with HCH have an identifiable mutation in the FGFR3 gene on chromosome 4p16.3. The remaining 30 per cent will either have a so far unrecognised mutation in the FGFR3 gene or a mutation in other as yet unidentified genes.

To a lesser or greater degree, the features of HCH may include:

• Short stature with an adult height in the range of 128 -151 cm (4 feet, 2 inches to 4 feet 11 inches);
• Disproportionate arms and legs with short, broad hands and feet;
• Macrocephaly (an enlarged head);
• Limitation of elbow movement;
• Lordosis (exaggerated curvature at the lower end of the spine);
• Increased joint mobility;
• Learning problems (it has not yet been determined whether this is in fact a feature of HCH).

It is not easy to diagnose HCH in very young children and may be even be missed in adults. Diagnosis is made by identifying the features known to appear in HCH together with radiological (x-ray) findings. DNA based testing can confirm the FGFR3 gene mutation but cannot be used to eliminate the diagnosis.

HCH is not a curable condition and treatment will be symptomatic for specific features. Surgical limb lengthening can be considered but is a drawn out and painful process. Human growth hormone therapy has been given to some children with HCH but has shown mixed results. A range of support for families, based on perception of the effect of being of short stature at school and in the wider community, is available. Families can obtain information about aids to ameliorate difficulties in access and operation of equipment from local and national statutory and support organisations.

Autosomal dominant.

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.

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