Genetic Diseases Affecting Ashkenazi Jews

List of Ailments That Are Included in Tests of Couples

By Forward Staff

Published August 02, 2013.
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Here is a list of diseases that are often screened for in Jewish couples who are planning to have children because of an elevated risk of carrying a recessive mutation. Researchers have identified many more genetic diseases affecting those of Ashkenazi heritage than those of Sephardic and Mizrahi descent. Among Sephardic Jews more commonality exists among ethnic subgroups such as Moroccan Jews or Iranian Jews, making universal screening panels for all Sephardic and Mizrahi Jews more difficult.

Not included on this list are some mutations that are not typically screened for before pregnancy, such as those on the BRCA1 and BRCA2 genes.

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Ashkenazi Disorders

• Bloom’s Syndrome
Bloom’s syndrome is a recessive disorder characterized by growth deficiency, sun sensitivity, immunodeficiency and a predisposition to diabetes and cancer. Genes in people with Bloom’s syndrome are more likely to mutate, causing chromosomes to break. The carrier rate is estimated at 1 in 110, according to the Center for Jewish Genetics, resulting in the disease manifesting itself in about 1 in 48,000 births.

• Canavan Disease Canavan disease, which is carried by 1 in 40 to 1 in 58 Ashkenazi Jews, affects the brain and central nervous system. Patients have a deficiency of the enzyme aspartoacylase, which is necessary for normal brain development. They cannot generate myelin, which insulates nerve cells and allows transmission of nerve impulses.

• Cystic Fibrosis
Cystic fibrosis (CF) is a progressive multisystem disorder caused by abnormal function of the CFTR protein, which causes the body to produce thick, sticky mucus in the lungs and digestive system. CF is no more common among Ashkenazi Jews than among other Caucasians. It is one of the most common genetic disorders among Jews and non-Jews alike. One in 28 is a carrier; 1 in 3,000 has CF.

• Dihydrolipoamide dehydrogenase deficiency
This is a type of maple syrup urine disease that presents in early infancy with repeated episodes of vomiting and abdominal pain as well as poor feeding, lethargy, low muscle tone and developmental delay. The cause is a mutation in the DLD gene, which makes a protein needed for enzymes essential to the cells’ energy production. The flaw leads to toxic levels of amino acids in tissues. Untreated, it can cause seizures, coma and death. Some dietary changes are helpful. One in 96 Ashkenazi Jews is a carrier.

• Familial Dysautonomia
Familial dysautonomia (FD, also known as Riley-Day syndrome) is a progressive neurogenetic disorder that affects the sensory and autonomic nervous systems. About 1 in 31 Ashkenazi Jews is a carrier of the FD gene and 1 in 3,700 has the disease. Intelligence is usually normal in affected individuals; however, learning disabilities are common.

• Familial Hyperinsulinism
Familial or congenital hyperinsulinism is an autosomal recessive genetic defect occurring in the Ashkenazi Jewish population, among others. About 1 in 66 Ashkenazi Jews is a carrier; 1 in 18,000 has the disease. The disease affects the body’s sulfonylurea receptors in the pancreas, which control the secretion of insulin to regulate glucose levels in the bloodstream. In individuals with the disease, beta cells of the pancreas keep secreting insulin, regardless of blood-sugar levels. This causes dangerously low blood-sugar levels, which can result in seizures, brain damage and death.

• Fanconi Anemia
Fanconi anemia is a fatal, recessive disorder that causes bone marrow failure and possible birth defects. One in 90 people of Ashkenazi Jewish ancestry carries a Fanconi anemia gene. One in 32,000 has the disease. Many affected children do not reach adulthood.

• Gaucher Disease
Gaucher disease (pronounced “go-shay”) is an inherited disorder caused by a defective gene which prevents the body from producing sufficient amounts of an important enzyme, glucocerebrosidase. That enzyme plays a critical role in the complex process the body uses to remove and recycle worn-out cells. The disease course is variable, ranging from no outward symptoms to severe disability and death. Gaucher disease affects all ethnicities. Gaucher disease type 1 is the most mild form of the disease and affects those of Ashkenazi Jewish descent in greater numbers. Approximately 1 in 16 is a carrier and 1 in 855 has Gaucher disease. Among the general population, approximately 1 in 100/200 is a carrier; about 1 in 60,000 has the disease.

• Glycogen Storage Disease, Type I
Glycogen is a carbohydrate that serves as one of the primary fuel reserves for the body’s energy needs. Stores of glycogen power the body during times of fasting and exercise. Glycogen storage disease type I (GSD I) is caused by an enzyme deficiency that prevents the body from completely breaking down stored glycogen into glucose, which the body metabolizes. This progressive buildup of glycogen can cause impaired growth, bleeding problems and enlarged liver and kidneys. In Ashkenazi Jews, the carrier rate is 1 in 71 and 1 in 20,000 has the disease.

• Joubert Syndrome
There are several types of Joubert syndrome, caused by mutations in different genes. Joubert syndrome 2 is most common in Ashkenazi Jews, and is caused by a mutation in the TMEM216 gene. It is a rare neurological disorder characterized by multiple brain abnormalities, including the absence or underdevelopment of the cerebellar vermis — an area of the brain that controls balance and coordination. The carrier rate is 1 in 92; 1 in 34,000 has the disease.

• Maple Syrup Urine Disease
Maple syrup urine disease (MSUD) is named for the characteristic sweet smell of the urine in affected children. It is caused by genetic mutations that prevent the body from breaking down three specific amino acids in the body. These products then build up to toxic levels, leading to the manifestations of the disease. MSUD is caused by mutations in four different genes. There are several forms of this disease, and the classic severe form is most common in Ashkenazi Jews. Carrier frequency is 1 in 81 while 1 in 50,000 has the disease.

• Mucolipidosis IV
ML4 is characterized by the deficiency of a transport protein that plays a crucial role in psychomotor development. One out of 100 Ashkenazi Jews is a carrier, but the disease rate is unclear because many cases may be confused with cerebral palsy or present with only mild symptoms.

• Nemaline Myopathy
There are several types of nemaline myopathy, caused by mutations in different genes. It primarily affects skeletal muscles, causing weakness (myopathy) throughout the body that can worsen over time. It is typically most severe in the muscles of the face, neck and limbs. Muscle problems associated with nemaline myopathy are caused by an abnormal buildup of thread-like structures (nemaline bodies) in certain muscle tissue. The carrier rate is 1 in 108; about 1 in 47,000 has the disease.

• Niemann-Pick
Niemann-Pick disease includes several subtypes, two of which (types A and B) stem from a deficiency of acid sphingomyelinase, an enzyme that breaks down a fatty substance called sphingomyelin. When the enzyme is deficient, the unprocessed fat accumulates, mainly in the spleen, lymph nodes and brain. About 1 in 100 Ashkenazi Jews is a carrier of Niemann-Pick Type A, which is neuro-degenerative and leads to death by 2 or 3 years of age. One in 40,000 has the disease. Type B is a milder disorder that does not affect the brain but results in complications of the liver, spleen, lungs and bone marrow. Additional variants of this enzyme deficiency exist, and severity depends on how much sphingomyelinase is present in the cells to process the fats.

• Spinal Muscular Atrophy
Spinal muscular atrophy (SMA) causes degeneration of motor neurons, the nerve cells in an area of the spinal cord known as the anterior horn. When the motor neurons break down, so does the link between the brain and the voluntary muscles — those we control. As the link between the brain, spinal cord and muscles breaks down, the muscles that are used for activities such as crawling, walking, sitting up and moving the head are used less and less and become weaker, or atrophy. About 1 in 41 Ashkenazi Jews is a carrier, which is similar to other Caucasian populations.

• Tay-Sachs
Tay-Sachs disease is caused by the congenital absence of a vital enzyme, hexosaminidase-A. Without the enzyme, the body cannot break down one of its fatty substances, which builds up abnormally in the brain and progressively impairs the central nervous system. The gene that causes the infantile form of the disease is present in about 1 in 30 Ashkenazi Jews in America. About 1 in 300 Sephardic Jews and people of non-Jewish descent are also carriers.

• Usher Syndrome
Usher syndrome comprises a group of diseases with a distinctive combination of hearing and progressive vision loss. The genes related to Usher syndrome provide instructions for making proteins that play important roles in normal hearing, balance and vision. They function in the development and maintenance of hair cells, which are sensory cells in the inner ear that help transmit sound and motion signals to the brain. In the retina, these genes are also involved in determining the structure and function of light-sensing cells called rods and cones. Most of the mutations responsible for Usher syndrome lead to a loss of hair cells in the inner ear and a gradual loss of rods and cones in the retina. Degeneration of these sensory cells causes hearing loss, balance problems and vision loss. Two specific forms of Usher syndrome are more common in the Ashkenazi Jewish population — Usher syndrome type 1F and Usher syndrome type III, whose carrier rates are 1 in 141 and 1 in 107, respectively. Disease frequency is 1 in 80,000 and 1 in 45,000, respectively.

• Walker-Warburg Syndrome
Walker-Warburg syndrome (WWS) is a rare type of congenital muscular dystrophy characterized by brain and eye abnormalities and muscle disease, particularly weakness and atrophy of voluntary muscles. Mutations in different genes lead to different forms of WWS, and the forms vary in regard to muscles involved, ages of onset and severity. Only the carrier frequency is known: 1 in 149.

Chana Wiesman, a genetic counselor at Montefiore Medical Center and The Program for Jewish Genetic Health of Yeshiva University and Albert Einstein College of Medicine, contributed to this list.

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