Hexosaminidase B (Sandhoff Disease)
Related Gene(s): HEXB
Sandhoff disease is a rare, recessively inherited neurodegenerative disorder caused by a deficiency of beta-hexosaminidase A and B that leads to a pathological accumulation of GM2 ganglioside. This disorder is clinically similar to Tay-Sachs disease. Features include progressive loss of coordination, seizures, difficulty swallowing, and poor pulmonary function. Affected individuals eventually become blind, severely mentally retarded, paralyzed, and unaware of their surroundings. Onset is typical at approximately 6 months of age, and average life expectancy is 3 years. Sandhoff disease is a pan-ethnic condition, with a carrier frequency of 1 in 300 people.
Enzyme analysis is performed by measuring the total hexosaminidase activity (Hex A and Hex B) in plasma (serum) or leukocytes using a synthetic flurogenic substrate (4-MUG). The Hex A activity percentage is measured by comparing the heat inactivated activity (Hex A) to the total hexasominidase activity. Carriers of Sandhoff disease have a characteristic high Hex A percentage activity (>75-80%) and low total hexosaminidase activity. Patients affected with Sandhoff disease have absent or extremely low total hexosaminidase activity (Hex A and Hex B) and a very high Hex A percentage activity (90-100%).
Prior to ordering prenatal testing, please contact our laboratory at 800-298-6470. Prenatal testing is available on direct and cultured CVS as well as cultured amniocentesis samples.
Chorionic villus sampling (CVS)
- If cultures are to be established at our laboratory, please submit at least 10 mg of direct CVS specimen
- If cultures are to be established externally, please submit 6-8 mg of direct CVS specimen and three or four T25 cultured flasks for confirmation testing (and two T25 cultured flasks of control specimen)
- If a direct specimen is unavailable, please submit three or four T25 cultured flasks (and two T25 cultured flasks of control specimen)
- If cultures are to be established at our laboratory, please submit at least 15 ml of whole amniotic fluid
- If cultures are to be established externally, please submit three or four T25 cultured flasks (and two T25 cultured flasks of control specimen)
Additionally, please send:
- Maternal blood: 5-10 mL in EDTA tube (lavender top) required to perform MCC studies on all prenatal samples and in case maternal confirmation studies are necessary
- Paternal blood: 5-10 mL in EDTA tube (lavender top) in case paternal confirmation studies are necessary
- Anticoagulated blood: 5-10 mL in ACD tube (yellow top) is preferred. Sodium (or lithium) heparin tubes (green top) or EDTA tubes (lavender top) are also accepted
- Ship at room temperature; sample must be received within 72 hours of collection
- If the sample cannot be sent within 72 hours, centrifuge immediately and freeze plasma and leukocyte pellets. Then ship frozen on dry ice
- 7-10 days