What is Chediak-Higashi Syndrome (CHS)?
Chediak-Higashi syndrome (CHS) is an extremely rare form of partial albinism that is accompanied by problems in the immune and nervous systems.
Albinism is a lack of color in the skin, hair, and eyes.
This specific type of albinism also causes vision problems such as sensitivity to light, reduced sharpness, and involuntary eye movement. There have been fewer than 200 reported cases of CHS around the world, according to the U.S. National Institutes of Health (NIH, 2012).
Types of CHS
There are two types of CHS: classic and late-onset.
The classic form is present at birth or occurs soon after birth.
The late-onset form occurs later in childhood or adulthood and is much milder than the classic form. People with the late-onset form experience minimal pigmentation changes and are less likely to develop severe, recurrent infections. However, adults with late-onset forms of the disorder have a significant risk of developing neurological problems such as difficulty with balance and movement, tremors, weakness in the arms and legs, and reduced intellectual capacity.
What Causes CHS?
CHS is an inherited condition that is caused by a defect in the LYST gene (also called the CHS1 gene). The LYST gene gives the body instructions about how to make the protein that is responsible for transporting certain materials to your lysosomes.
Lysosomes are structures inside some of your cells that break down toxins, destroy bacteria, and recycle worn-out cell components. The defect in the LYST gene causes the lysosomes to become too large. The enlarged lysosomes interfere with normal cell functions. Enlarged lysosomes in immune system cell structures prevent cells from seeking out and killing bacteria and the body is not able to protect itself from recurring infections.
In pigment cells, abnormally large structures called melanosomes (related to lysosomes) produce and distribute melanin, the pigment that gives color to the skin, hair, and eyes. People with CHS have albinism because melanin is trapped within the larger cell structures.
Chediak-Higashi is an autosomal recessive inherited disorder. Parents of a child with this type of genetic disorder both carry a copy of the defective gene, but they usually do not show signs of the condition themselves (NIH, 2008).
If only one parent passes the defective gene down to you, you will not have the syndrome but you may be a carrier. This means that you can pass the gene on to your children.
What Are the Symptoms of CHS?
Symptoms of classic CHS include:
- brown or light-colored hair with a silvery sheen
- light colored eyes
- white or grayish skin tone
- nystagmus (involuntary eye movements)
- frequent infections in the lungs, skin, and mucous membranes
Other symptoms that infants or young children with CHS may experience are:
- poor vision
- photophobia (eyes are sensitive to bright light)
- slowed mental development
- blood clotting problems resulting in abnormal bruising and bleeding
Roughly 85 percent of children with CHS reach a severe stage called the accelerated phase. Scientists think the accelerated phase is triggered by a viral infection (NIH, 2012).
During this phase, the defective white blood cells divide rapidly and uncontrollably, which can cause:
- abnormal bleeding
- serious infections
- organ failure
Older children and adults with CHS have milder symptoms, less noticeable pigmentation issues, and fewer infections. However, people with late-onset form of this disorder develop seizures and nervous system problems that may cause:
- tremors (involuntary shaking)
- difficulty walking
How Is CHS Diagnosed?
To diagnose CHS, a doctor will first evaluate your medical history to look for other indicators of the disease, such as frequent infections. A physical exam and certain tests are then performed to make a diagnosis. A physical exam can show signs of a swollen liver or spleen, or jaundice (yellowing of skin and eyes). Tests may include:
- complete blood count to identify abnormal white blood cells
- genetic testing to identify the defective LYST gene
- ophthalmologic exam (eye exam) to determine reduced eye pigmentation or presence of involuntary eye movement
How Is CHS Treated?
There is no cure for CHS. Treatment consists of managing symptoms.
Antibiotics will be used to treat infections, and corrective eye lenses may be prescribed to improve vision. Bone marrow transplants may help treat defects in the immune system. However this procedure is most effective when performed before a person develops the accelerated phase of the disorder.
If your child is in the accelerated phase, your doctor may prescribe antiviral medications and chemotherapy drugs to try to minimize the spread of the defective cells.
Long-Term Outlook for CHS Patients
Most children with the classic form of CHS die within the first 10 years of their lives as a result of chronic infections or organ failure. Some children do live longer than 10 years.
People with late-onset CHS may live with the disorder into early adulthood, but typically have shorter lifespans due to complications of the disorder.
Contact your doctor about genetic counseling if you have CHS or if you have a family history of the syndrome and are planning to have children. Genetic testing may be available to detect whether you are carrying the defective LYST gene, and also to determine the likelihood that your child will inherit the syndrome. Prenatal testing may also be an option for at-risk pregnancies. This type of testing involves analyzing a small sample of DNA extracted from the amniotic fluid (the clear fluid that surrounds and protects a baby in the womb) to test for mutated genes.
Scientists have identified more than 30 possible mutations in the LYST gene that cause CHS. The specific gene mutation in your family must be identified before any genetic or prenatal testing is available. (Introne WJ, et al., 2012)