Muscle-eye-brain disease (MEB) is a type of congenital muscular dystrophy. It is characterized by the degeneration of muscles that help in movement (skeletal muscles), vision abnormalities, and delayed brain development.
Genetic mutations in MEB
MEB is a genetic condition caused by a mutation in the POMBGNT1 gene, which carries the instructions necessary to make an enzyme called O-linked mannose N-acetylglucosaminyltransferase 1. The role of this enzyme is to activate alpha-dystroglycan by adding a sugar molecule to it, a process called glycosylation.
Alpha-dystroglycan is a protein that provides structural support to the cells in skeletal muscles and directs the movement of nerve cells in the brain during early stages of development. Glycosylation of alpha-dystroglycan is vital for the protein to perform its function efficiently.
Mutations in POMGNT1 cause the O-linked mannose N-acetylglucosaminyltransferase 1 enzyme not to work properly. As a result, alpha-dystroglycan is not glycosylated. This affects its function and leads to the symptoms associated with MEB.
Inheritance of MEB causing mutations
Every cell in the human body has 23 pairs of chromosomes that carry a string of genes. Each parent contributes one chromosome to every pair. Of the 23 chromosomes, 22 are called autosomes, and one pair is the sex chromosome that determines an individual’s gender. There are two copies of every gene on the autosomes, one inherited from each parent.
The POMGNT1 gene is located on chromosome 1, an autosome. Therefore, there are two copies of the POMGNT1 gene in every individual. MEB is inherited in an autosomal recessive manner, meaning that both copies of the POMGNT1 gene must be mutated for the disease to develop.
A person with one copy of the mutated gene is called a carrier, and he or she may not show any symptoms. A couple where both individuals are carriers has a 25 percent chance of either having a child with MEB or a healthy child who does not inherit the mutation. They have a 50 percent chance of having a child who is also a carrier of MEB.
Genetic testing can be used to detect these mutations. Genetic counselors can explain the inheritance pattern of this mutation to help couples make informed health and family decisions.
Last updated: Aug. 26, 2019
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