Children and adults
with Achondroplasia have short upper arms and thighs, a normal length
back, a large head, and a characteristic face with depressed nasal
bridge, small nose and large forehead. They appear to have large
muscles for their leg length. They are of normal intelligence and
health. Achondroplasia is caused by a mutation of a single gene and
has a dominant pattern of inheritance. This means that, on average,
half the children of a parent with Achondroplasia will also be
affected. In most cases, however, there is a new mutation, without any
family history and it seems that this particular gene is one of the
most unstable in the human complex.
At present,
treatment depends primarily on new surgical techniques of limb
lengthening. Growth hormone treatment may improve short term growth
rate, especially if started at an early age. However, it is not yet
known whether this improves final height and growth hormone use in
this condition is therefore still being evaluated through clinical
trials.
Hypochondroplasia
This is a similar
syndrome to Achondroplasia but the physical characteristics and short
stature are less marked. Like Achondroplasia, the short legs are
responsible for the short stature. The face is normal (though it has
some tell tale features to the experienced eye) and children with
Hypochondroplasia often may be diagnosed as being very short normal
people.
Hypochondroplasia is also inherited as a dominant gene, but seems to
be separate from the Achondroplasia gene; the two conditions very
seldom appear in the same family. In Hypochondroplasia, one of the
parents frequently has the disorder.
There is no certain
way of confirming what is sometimes a difficult diagnosis. 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. The effect of
growth hormone treatment is being evaluated through clinical trials.
