What is molecular genetic assessment?

Molecular genetic assessment allows us to look closely at a person's genes to see if there is a mutation that causes a certain condition.

This assessment, sometimes called DNA testing, makes it easier to diagnose genetic conditions correctly. A correct diagnosis helps us provide the best treatment for your child's condition.

Molecular genetic assessment also helps us tell you what your child will be like as he grows up. We will have a better chance of finding out what other conditions might affect him, and what his quality of life will be.

How do genetics affect achondroplasia?

Achondroplasia is the most common form of short-limbed dwarfism. It affects about one in every 15,000 babies. More than 80% of the time, these babies have parents who are average height.

It is impossible to know simply by looking at parents if their child will have achondroplasia.

Achondroplasia is caused by a change (mutation) in the gene called fibroblast growth factor receptor 3 (FGR3). This mutation is often what doctors call "spontaneous" - it is not a change passed down by parents who have the condition themselves. The mutation is more likely to occur in the sperm of fathers older than age 35.

A protein called fibroblast growth factor (FGF) stimulates and controls how cartilage grows. It helps determine both the length and shape of bones. When FGR3 is not normal, the fibroblast growth factor cannot work the way it usually does.

This causes some of the typical growth patterns and problems of achondroplasia:

  • Short arms and legs
  • A narrow opening in the bones of the back that surround the spinal cord
  • Compression of the nerves going into the legs due to this narrow opening

How do you use genetic molecular assessment with achondroplasia and other similar problems?

There are two dwarfing conditions that look like achondroplasia. Hypochondroplasia is a milder form of dwarfism. Thanatophoric dysplasia is a much more severe form of dwarfism that often leads to death in newborn babies.

Like achondroplasia, these two conditions are the result of mutations in the gene called FGR3. When doctors are unsure whether a child has hypochondroplasia or achondroplasia, this genetic analysis can distinguish between the two conditions and help us find the right treatments.

Parents who know they have a higher than usual chance of having a baby with achondroplasia or another skeletal dysplasia can also choose to have DNA testing during early pregnancy. This technique is called chorionic vilus sampling.

Genetic molecular assessment can provide the basis for genetic counseling to help your family understand both the causes of a genetic disorder and the chances it may happen again during another pregnancy.