Bone growth and achondroplasia

What is achondroplasia?

When a baby is developing in the womb, the skeleton first forms out of cartilage, which then this develops into bone (except in certain areas such as the nose or ears where cartilage remains).

In achondroplasia, this process doesn't happen as it should, especially in the long bones of the arms and legs. Instead, the cartilage cells in the growth plates turn only very slowly into bone.

Achondroplasia affects one child in 20,000.

Symptoms

The result is short bones in the arms and legs, especially the upper arms and thighs, making a person short but with a nearly average-size torso.

Other bone differences typically include a large head, prominent forehead and a nose that's flat across the bridge.

These bone abnormalities can lead to a range of health problems, as well as psychological trauma caused by the stigma of looking different from the crowd. Most children with achondroplasia have normal intelligence.

Babies with achondroplasia may have poor muscle tone and be slow to stand and walk. Spinal problems can develop, and the lower part of the legs may become bowed. There may be dental problems because teeth are often crowded and poorly aligned. Middle ear infections occur frequently and can cause mild to moderate hearing loss.

Causes and risk factors

In approximately 75 per cent of cases the problem results from a new mutation of a gene (that is, neither parent carries the faulty gene), but in some cases a child inherits achondroplasia from a parent who also has the condition. There is also a link with older fathers, over the age of 40.

Treatment and recovery

No treatment can make the bones grow to a normal size. Growth hormone treatment doesn't have much effect on this condition.

Surgery to lengthen the legs can increase height by as much as 30cm, but it involves months and years of wearing a special metal frame pinned through the leg bones. This can be painful and is hugely demanding on a small child and their family.

Other operations may be necessary to prevent complications, but the main focus is on adapting to a world designed for taller people.