Skeletal dysplasia

Achondroplasia (ACH) & Hypochondroplasia (HCH)

Skeletal dysplasia is a term used to describe a range of more than 200 very rare conditions which affect cartilage and bone growth. Achondroplasia (ACH) and Hypochondroplasia (HCH) are two of the more frequently seen skeletal dysplasias but are still very rare overall. They are known as short limb dysplasias because children with this condition have an average-sized torso (chest and abdomen) but smaller arms and legs.

What causes these skeletal dysplasias?

ACH and HCH are caused by genetic disorders that affect girls and boys equally. The problem arises in one of the chromosomes that are inside almost every cell in the human body. These chromosomes contain DNA which is organised into genes. (See the back page for a guide to these terms.) A change in a specific gene causes the problems in growth and development associated with these conditions.

How will these skeletal dysplasias affect a child’s height?

Without treatment, people with ACH will eventually reach an average height of just over 132cm (4ft 4in) for men and 124cm (4ft 1in) for women. In HCH, the adult height reached is often greater than for people with ACH and ranges from 118–152cm (3ft 10in – 5ft).

How are these skeletal dysplasias diagnosed?

These conditions are usually not diagnosed until after a child has been born. A doctor will normally make a diagnosis based on the child’s appearance, and an examination of X-rays of the bones. In addition to shorter arms and legs, children with ACH and HCH tend to have larger heads than average, and the shape or size of the hands may also be affected.

The appearance of children with mild HCH can be a little similar to children with a more common condition known as idiopathic short stature (ISS) but a more detailed examination should be able to confirm the diagnosis of HCH.

The importance of early treatment for short height

For children with ACH or HCH, the earlier treatment is started, the better the prospects for increasing the height they will eventually reach. Children who are shorter than normal are often seen by a paediatric endocrinologist, who is a doctor specialising in treating children with growth problems.

Helping a child to grow

Some children with ACH or HCH may be given growth hormone treatment to boost their growth. Growth hormone treatment can achieve a gain in height in the first year of treatment, and continuing with the treatment may be beneficial in the longer term. A child with HCH can reach normal adult height with growth hormone injections but children with ACH will probably remain below normal adult height even with treatment. However, the extra height gained by children with ACH will certainly improve their ability to carry out many daily activities.

When children with ACH or HCH are treated with growth hormone, a gain in height can be achieved without affecting the difference in proportion between the torso and the arms and legs.

Growth hormone injections are normally given once-daily, in the evening. At the beginning parents are trained to give these injections when the child is very young. Later on, children can inject themselves when they feel confident enough. Devices are now available that make injecting growth hormone much simpler, more comfortable and less painful. This has been achieved through advances in design such as automated needle insertion and the use of very fine needles. There is a wide choice of devices available, and whilst some require mixing before use and refrigeration once opened, others do not.

To help the doctor select an injection device that matches your requirements, it may help to read the page discussing the features of the various devices.

Meeting the challenge of growth problems

If a child is shorter than other children of the same age, and also looks a bit different, this can have an impact on the whole family. Children with ACH or HCH may experience emotional problems, bullying and difficulties with daily activities such as sports. For these reasons, it’s important to explain to a child that things can be improved by continuing with the growth hormone treatment. In order to promote a child’s emotional development and encourage independence, remember to act towards a child according to the age they actually are, not the age they look.

APROM ID# 1503. December 2009.