Cartilage Hair Hypoplasia, or McKusick type syndrome, is a genetic bone growth disorder resulting in short stature and other skeletal abnormalities, as well as fine, sparse hair and compromised immune system function. It was first described by McKusick in 1965.
Those with cartilage hair hypoplasia are born with short limbs and subsequently short stature. This is due to malformation of the cartilage at the end of the long bones of the arms and legs. This affects the development of the long bone, resulting in shortened length. Individuals with cartilage hair hypoplasia can be unusually flexible in their joints due to the lack of cartilage.
One of the defining features of cartilage hair hypoplasia is the presence of fine, sparse hair. Individuals usually have hair that is lighter in color than their family members. This is due to a lack of an inner core in the hair structure. This results in a lighter appearance since the core contains some of the pigments that contribute to hair color, as well as thinner strands of hair.
The extent of the immune deficiency in those with cartilage hair hypoplasia can vary from mild to severe. In severe cases, patients are prone to repeated and persistent infections and are considered to have severe combined immunodeficiency (SCID). Most individuals with cartilage hair hypoplasia, even in milder cases, suffer from infections in the respiratory system, ears, and sinuses. Those with cartilage hair hypoplasia may also have gastrointestinal problems and a higher risk of developing cancer.
Cartilage hair hypoplasia is quite rare, occurring in only 1 out of 20,000 births. It is significantly more common in certain Amish populations, occurring as high as 1 in 1,300 births. Cartilage hair hypoplasia is a genetic disorder linked to mutations in the RMRP gene. It is inherited in an autosomal recessive pattern, which means individuals must carry recessive two copies of the gene in order to express the disorder.
At the Paley Institute we successfully treat the orthopedic difficulties associated with cartilage hair hypoplasia. We perform extensive limb lengthening of both the femurs and tibias to correct the short stature.