What is cartilage-hair hypoplasia?
Cartilage-hair hypoplasia (say: hie-po-PLAY-zee-a), or CHH, is a genetic condition that results in:
- short stature (height)
- shorter arms and legs than expected
- fine, sparse hair
- anemia, a low number of red blood cells
- problems with the immune system
Another name you may hear for this condition is metaphyseal chondrodysplasia, McKusick type.
CHH is quite rare in the general population. In some populations, it is more common. In the Old Order Amish population about one in 1,300 newborns have CHH. In people of Finnish descent, it affects one in 20,000 newborns.
How cartilage-hair hypoplasia affects the body
Height and body shape
Babies with CHH are born with shorter arms and legs than normal. During childhood, the long bones of the arms and legs grow at a much slower pace than usual. This leads to short stature (height) as well as relatively shorter limbs. The ribs are also affected, leading to flaring of the lower chest. People with CHH may also have bowed legs, be more flexible than usual, and have shorter hands and feet. Average adult height is between 40 and 60 inches (3 feet 4 inches to 5 feet).
Hair
The scalp hair, eyebrows, and lashes of people with CHH are sparse, fine and light-coloured because the core of the hair, which contains the pigment, is missing.
Blood and the immune system
Most people with CHH have problems with the function of the immune system. These problems vary from mild to severe and may include the following:
- Impairment of specialized cells called T-cells, which play an important role in helping the body's immune system to fight infection. This is called cellular immunodeficiency.
- Abnormally low levels of certain white blood cells (neutropenia and lymphopenia).
- Lower resistance to certain infections, such as chickenpox.
Because of their low levels of specialized immune cells, people with CHH get infections more often. However, as they grow older, people with CHH become more able to resist infections.
In early childhood, most people with CHH have severe anemia because they have low levels of red blood cells. Symptoms of anemia include paler skin and decreased energy.
Gastrointestinal problems
Some people with CHH have gastrointestinal problems. These problems may include:
- an inability to absorb nutrients properly
- celiac disease, an intolerance of a protein called gluten that is found in wheat and other grains
- Hirschsprung disease, an intestinal disorder that causes severe constipation, intestinal blockage and enlargement of the colon
- narrowing of the anus (anal stenosis)
- blockage of the esophagus, the passage that brings food from the mouth to the stomach (esophageal atresia)
Cancer risk
People with CHH have a higher risk of developing cancer, particularly certain skin cancers (basal cell carcinomas), cancer of blood-forming cells (leukemia) and cancer of immune system cells (lymphoma).
Intellectual development
Children with CHH have normal intelligence and attend regular schools. They may need some modifications because of their height, such as sitting at the front of the classroom.
Cartilage-hair hypoplasia is a genetic disorder
Genetic means related to genes. Each of us inherits our genes from our parents. They provide our bodies with instructions that influence our health, looks and behaviour.
CHH occurs due to a mutation (change) in a gene known as RMRP gene. Each person has two copies of the RMRP gene, one inherited from their mother and the other from their father.
CHH is inherited in an autosomal recessive pattern. This means that:
- A person with CHH has a mutation in both copies of the RMRP gene.
- Each parent carries a mutation in one copy of the RMRP gene. The other copy of the RMRP gene works normally and because of this, the parent does not show signs and symptoms of CHH. This person is called a carrier of CHH.
Cartilage-hair hypoplasia diagnosis
A diagnosis of CHH is made on the basis of the physical examination and X-ray findings. This can be confirmed by DNA testing of the RMRP gene (blood test).
CHH can sometimes be diagnosed before birth
Before birth, CHH may be diagnosed by testing DNA taken from the fetus. This can be obtained in one of the following ways:
- by amniocentesis after the 15th week of pregnancy
- by chorionic villus sampling (CVS) between the 11th and 14th week of pregnancy
These methods are used for high-risk pregnancies, for instance if the parents have another child diagnosed with CHH. In these cases, the mutations in the RMRP gene must be known. This means that genetic testing on the child must be done.
CHH can sometimes be diagnosed before birth using ultrasound. Babies with CHH have shortening and bowing of the thighbone, which can sometimes be seen on ultrasound.
Treatment of cartilage-hair hypoplasia
Children with CHH can lead fulfilling lives if they receive attentive, informed care from their parents and health-care providers. They should be carefully followed because of the possibility of serious infections and cancer.
The goals of treatment are:
- to help children with CHH adapt socially and physically
- to prevent and treat any complications
Various specialists work together as a team to help children with CHH. Your child may need to see an immunologist, an orthopaedic surgeon, a physical therapist and a geneticist from time to time.
Treatment for problems with blood and the immune system
A few people with CHH develop severe anemia and may need several blood transfusions.
Children with CHH should not be immunized with live vaccines until they have had a complete evaluation by an immunologist. Live vaccines include chickenpox vaccine and measles, mumps and rubella (MMR) vaccine. Speak to your doctor for more information. Chickenpox (varicella) and shingles (herpes zoster) infections need to be managed by the treatment team.
In some cases, bone marrow transplantation can be done to correct severe immune deficiency and anemia, but it has no influence on bone changes.
Treatment of bone and joint problems
Surgical correction of leg deformities might be considered, but people with CHH need extra post-operative care to avoid infections. Physiotherapy can help with limited joint movements. People with CHH may need pain medicine to help with joint pain. This will be carefully monitored by the doctor.
Treatment of gastrointestinal problems
Gastrointestinal problems are treated according to their symptoms. If the person has Hirschsprung disease, they will probably need surgery (an operation).
Coping with cartilage-hair hypoplasia
Children with visible differences like short stature can have difficulties in school and society. Encourage your child to participate in activities with other children the same age. As well, try to physically adapt your child's surroundings to support your child and encourage independence. Speak to your health care team if you need help or advice or if you are having trouble coping.
Genetic counselling for cartilage-hair hypoplasia
People with CHH and their families should consider assessment by a geneticist and genetic counsellor. They can help with the following:
- confirming the diagnosis
- discussing the natural history of the disease
- evaluating the risk that future children will also be affected
- discussing available options for managing the disease
Resources and support
The following organizations and sites can offer more information, support, and contact with other affected individuals and their families.
The Human Growth Foundation
Little People of Canada
Little People of Ontario
www.littlepeopleofontario.com.