Achondroplasia is a rare genetic disorder that causes short stature and bowed legs. It is the result of a genetic mutation that is more likely to arise in the children of older men.

Dwarfism refers to restricted growth that is due to medical or genetic causes. Although dwarfism has a range of possible causes, about 90% of cases are the result of achondroplasia. This genetic disorder can pass through families, but most people have achondroplasia without having a parent who shares the condition.

In this article, we discuss the genetics of achondroplasia, including the mutation that causes it. We also explain how heritable the condition is, who is most likely to get it, and what symptoms it causes.

An image of a person with achondroplasia.Share on Pinterest
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A 2021 review explains that achondroplasia is a condition that affects bone growth. It can lead to several symptoms, including:

The review notes that these symptoms can have a significant effect on people’s quality of life and their ability to perform daily tasks. For example, the combination of shorter stature with stiff elbows can lead to difficulties reaching items. Bowed legs can make walking difficult and painful.

People with achondroplasia can also develop lumbar spinal stenosis as a result of abnormal bone growth. This condition causes a compression of the nerves in the spine, leading to pain, weakness, and mobility problems. It is a serious complication and the leading cause of later-life disability in people with achondroplasia.

Other complications of achondroplasia include sleep apnea and hearing problems. People with the condition also have a life expectancy that is about 10 years shorter than that of the general population.

There is no cure for the condition. However, doctors can recommend various treatment options for the symptoms and complications of achondroplasia. These may include:

  • spinal fusions
  • guided bone growth
  • ear tubes for middle ear problems

These treatments can reduce symptoms in people with achondroplasia and improve their ability to perform daily tasks.

Achondroplasia is the result of a mutation in the FGFR3 gene.

Genetic mutations refer to changes in genes that cause differences among individuals. Genes provide instructions for the body’s cells and influence how they grow, interact, and die. Genetic mutations can influence any stage in this process and produce a wide range of characteristics.

The FGFR3 gene provides instructions for the fibroblast growth factor 3 (FGFR3) protein. This protein influences how cells divide, mature, and form structures, such as bones. FGFR3 gene mutations cause FGFR3 to become overactive, which can affect growth.

People with the achondroplasia-causing mutation in their FGFR3 gene have reduced growth in some of their bones.

Genetic mutations occur all the time and are usually harmless. They can arise for no clear reason. However, there is some inconclusive evidence suggesting that prenatal exposure to pollutants could increase the risk of FGFR3 gene mutations. Therefore, this is a possible risk factor for achondroplasia, although more research is necessary to confirm the association.

Achondroplasia can pass through families because parents pass genes on to their children. There is a chance that someone with an FGFR3 gene mutation will pass it onto their child, who may then develop the condition.

However, achondroplasia is rare, and a 2020 review states that about 80% of people with the condition have parents with average stature. These parents have a very low chance of having another child with the condition.

However, the matter is more complex when one or both parents have achondroplasia. If both parents have the condition, there is a:

  • 25% chance that the child will have average stature
  • 50% chance that the child will have achondroplasia
  • 25% chance that the child will have homozygous achondroplasia, which causes death during infancy

Other genetic factors can affect the odds of developing achondroplasia. The age of the father can increase the likelihood of a person developing the FGFR3 gene mutation despite having parents without achondroplasia. Fathers over the age of 34 years have a much higher likelihood of having children with the FGFR3 gene mutation who develop achondroplasia as they age.

Research suggests that about 1 in every 15,000 children will have the condition. However, 1 in every 1,875 children whose fathers are over the age of 50 years at the time of their birth will have some form of skeletal dysplasia. Skeletal dysplasia refers to a group of conditions that affect the bone and cartilage cells, including achondroplasia.

It remains unclear whether other factors affect the likelihood of developing achondroplasia.

A comprehensive 2020 review of the evidence suggests that achondroplasia is more common in certain parts of the world, such as North Africa, sub-Saharan Africa, and the Middle East. However, the authors state that the quality of data from these regions is poor and that more research is necessary.

Achondroplasia is a rare genetic condition that affects bone growth. It causes several problems that affect daily living, such as difficulty walking and reaching.

People with achondroplasia can pass the genetic mutation responsible for the condition to their children. However, many children of people with the condition will not develop it.

The risk of a child having achondroplasia increases if the father is over 35 years of age at the time of their birth.