Genetics Northern California

Cartilage-hair hypoplasia

Cartilage-hair hypoplasia (CHH) is characterized by short limbed, short stature, light-colored and sparse hair, impaired immunity, and anemia. The limbs are shortened in all segments including fingers and toes. Individuals may also have mild scoliosis (abnormal curving of the back), genu varum (bowed legs), lumbar lordosis, and chest wall abnormalities (prominent sternum with flaring of the lower ribs). The immune system is often, but not always impaired in CHH. The impairment is in the cellular community or T-cells; humoral immunity is intact. There is increased susceptibility to infection in childhood (usually not in adulthood), especially to the varicella virus. Though rare, individuals with CHH can also have Hirschsprung's disease (an absence of nerve cells in the intestines which leads to constipation). There is an increased risk for cancer in CHH, particularly for leukemia and lymphoma. Anemia is another possible complication in early childhood, but it usually resolves without intervention prior to adulthood.

Cause
Cartilage-hair hypoplasia (CHH) is an autosomal recessive condition. Mutations causing CHH have been found in the gene for mitochondrial RNA-processing endoribonuclease (RMRP). This gene is isolated on chromosome 9. CHH has a high incidence in the Finnish and Amish populations, but has been diagnosed in individuals of almost all ethnic backgrounds. There has been shown to be a very wide range of severity in the condition -- with some individuals being very mildly affected and others having all of the described features and medical issues.

Diagnosis
The diagnosis of cartilage-hair hypoplasia (CHH) is made by clinical symptoms and radiological (x-ray) features:

  • short tubular bones

  • flared, scalloped, sclerotic metaphyses - most pronounced at knees and ankles

  • increased lumbar lordosis

  • normal vertebral bodies

  • increase of interpediculate distances, less obvious than normal

  • horizontally tilted sacrum

DNA testing is not required for diagnosis, but may be useful to confirm a diagnosis or for prenatal testing.

Prenatal Diagnosis
Prenatal mutation testing through chorionic villi sampling (CVS) or amniocentesis is available for couples to have had mutations detected in a previous child or when the mutations are known in an affected parent(s). There are no reported cases of prenatal ultrasound detection of CHH, however it is possible that the short limbs of CHH might be detected in a 3rd trimester ultrasound.

Treatment/Services
Children with cartilage-hair hypoplasia (CHH) should be monitored by orthopedics for leg bowing. Surgical correction may be recommended if the bowing is significant. It is recommended that live vaccines be avoided. These vaccines can be considered only after a thorough evaluation by an immunologist. Bone marrow transplant is used to treat the most severe immunity problems. Bone marrow transplant does not change the skeletal features of CHH.

Some of the most difficult aspects of having CHH are not the medical issues, but rather the environmental and social issues that arise for a person of short stature and/or with an orthopedic disability. It is important to work with the family on their adjustment to the diagnosis and what that will mean for the child and their family. Individuals with CHH and their families should receive assistance in developing strategies for functioning in a world made for taller people. Participation in household, school, and social activities are examples of activities that may all be significantly impacted by the condition. Stools, extenders for reaching, and extra time to get to class, are all examples of modifications that may be required. In addition to the functional aspects, being short-statured and orthopedically handicapped carries great stigma. It is important to help the people with CHH and their families to mentally and emotionally prepare themselves for the teasing, staring, and ignorance they may face and to learn coping mechanisms and reactions to these behaviors.

RESOURCES

Genetics Home Reference: Cartilage-hair hypoplasia - General information about CHH provided by the National Library of Health. Also includes links to many related sites.

Little People of America (LPA) is the support organization for all people of short stature and their families. This organization can be extremely helpful in assisting with social adjustment and, more than anything else, letting people with short stature know that they are not alone in their circumstances.