Achondroplasia is an autosomal dominant disorder associated with short stature. It is caused by a mutation in the fibroblast growth factor receptor 3 (FGFR-3) gene. This results in abnormal cartilage giving rise to:

• short limbs (rhizomelia) with shortened fingers (brachydactyly)
• large head with frontal bossing and narrow foramen magnum
• midface hypoplasia with a flattened nasal bridge
• 'trident' hands
• lumbar lordosis

In most cases (approximately 70%) it occurs as a sporadic mutation. The main risk factor is advancing parental age at the time of conception. Once present it is typically inherited in an autosomal dominant fashion.

Treatment

There is no specific therapy. However, some individuals benefit from limb lengthening procedures. These usually involve application of Ilizarov frames and targeted bone fractures. A clearly defined need and end point is the cornerstone of achieving success with such procedures.

Many questions relating to autosomal dominant conditions are based around one of the parents being affected. With achondroplasia both parents are often affected which can make the interpretation slightly trickier.

As an autosomal dominant condition, two affected parents can expect:

• 1 in 4 chance of an unaffected child
• 1 in 2 chance of an affected heterozygous child
• 1 in 4 chance of an affected homozygous child. With achondroplasia children unfortunately don't live past the first few months of life