Cartilage and Bone Disorders
Mostly at birth by radiological examination.
Usually surgical limb lengthening, growth hormone in trials.
Many bone disorders affect growth: they are mostly rare and often inherited. They are known as skeletal dysplasias, and the best known is Achondroplasia.
Physical characteristics include short upper arms and thighs, a normal length back, a large head, and a depressed nasal bridge, small nose and large forehead.
Those with this condition appear to have large muscles for their leg length. Intelligence and general health are not usually affected.
Achondroplasia is caused by a mutation of a single gene and has a dominant pattern of inheritance. This means that, for adults with the condition, there’s around a 50% chance of any children you have also being affected. However, most cases are caused by a new mutation, without any family history, and this particular gene seems to be one of the most unstable in the human make-up.
Current treatment depends mainly on new surgical techniques for limb lengthening. Growth hormone treatment may improve short-term growth rate, especially if started early enough. However, it is not yet known whether this improves final height, and growth hormone use is still being evaluated in clinical trials.
This is a similar syndrome, with less noticeable physical characteristics and short stature. Like Achondroplasia, short stature is because of the short legs. The face doesn’t look out of the ordinary (although it has some tell-tale features if you know what to look for) and children with Hypochondroplasia may often be simply diagnosed as ‘just very short.’
Hypochondroplasia is also inherited as a dominant gene, but it seems to be separate from the Achondroplasia gene in that the two very seldom appear in the same family. With Hypochondroplasia, one of the parents often has the disorder.
Definite, confirmed diagnosis can often be tricky. The most helpful feature is comparison of sitting-height and leg-length centiles. While in Achondroplasia the x-ray signs are marked and characteristic, in Hypochondroplasia they are minimal. Clinical trials are currently evaluating the effectiveness of growth hormone treatment.
Other Skeletal Dysplasias
There are more than 100 of these conditions, of which Achondroplasia and Hypochondroplasia are two of the most common. Other bone disorders are rarer; some affect limbs only, some the trunk and others both.
To date, none of these conditions have any specific treatment, although surgical limb lengthening is potentially the most promising, while, again, the use of growth hormone is being evaluated in clinical trials.
The following booklets are available to download here courtesy of the Restricted Growth Association.