Cartilage-Hair Hypoplasia

Cartilage-Hair Hypoplasia (CHH) is an inherited disorder that results in extremely short stature with shortened arms and legs as well as other skeletal abnormalities. People with CHH may also have fine, sparse hair and mild to severe immune system deficiency. As a result, they have a much higher risk of infections and autoimmune disorders. They also have a higher risk of developing certain kinds of cancers. Individuals with CHH may have gastrointestinal problems such as Hirschsprung disease, an intestinal disorder that causes severe constipation, intestinal blockage, and enlargement of the colon. Intellectual disability or learning problems may occur in people who have the severe spectrum of CHH. The life expectancy of individuals with CHH may be decreased due to the risk of infections and cancers. There is no cure for CHH but medical surveillance and care may help to improve some symptoms and overall condition of life. CHH is caused by pathogenic variants in the RMRP gene.

CHH is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

There are generally no signs or symptoms associated with being a carrier for Cartilage-Hair Hypoplasia. However, the risk to have a child affected with CHH is increased. Testing of reproductive partners is recommended for carriers of CHH.

CHH is a rare condition. It is most common in the Old Order Amish population, affecting about 1 in 13,000 newborns. Studies also indicate that CHH is common in the Finnish population, occurring in 1 in 20,000 individuals.

Genetics Home Reference: Cartilage-hair hypoplasia (http://ghr.nlm.nih.gov/)

OMIM [CARTILAGE-HAIR HYPOPLASIA: 250250] (http://www.ncbi.nlm.nih.gov/omim)
Gene Reviews: Cartilage-Hair Hypoplasia - Anauxetic Dysplasia Spectrum Disorders (http://www.ncbi.nlm.nih.gov/books/NBK1116/)

• Full gene sequencing