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Hereditary Motor and Sensory Neuropathy with Agenesis of the Corpus Callosum

  • What is Hereditary Motor and Sensory Neuropathy with Agenesis of the Corpus Callosum?

    Hereditary motor and sensory neuropathy with agenesis of the corpus callosum (HMSN/ACC), also known as Andermann syndrome, is a very rare inherited disorder that affects the nerve cells. Symptoms begin appearing in individuals affected by this disorder early in life. They include low muscle tone, absent reflexes, muscle weakness, reduced sensory function in their limbs, intellectual disability, and abnormal development of corpus callosum, which is the tissue connecting the left and right halves of the brain. As individuals age, they may develop contractures and scoliosis. Affected individuals share characteristic facial features which include facial asymmetry, long face, narrow forehead, large ears, drooping of the eyelids, and increased distance between the eyes. Children affected with HMSN/ACC are able to learn how to walk, though at a later age than most children. By adolescence, however, most individuals are wheelchair bound. During adolescence, affected individuals develop hallucinations, psychosis, and other psychiatric symptoms. Death usually occurs in third or fourth decade of life. There is no cure for HMSN/ACC; however medical surveillance and care may help to improve some symptoms and overall condition of life. HMSN/ACC is caused by pathogenic variants in the SLC12A6 gene.

  • How is Hereditary Motor and Sensory Neuropathy with Agenesis of the Corpus Callosum inherited?

    HMSN/ACC is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

  • What does it mean to be a carrier?

    There are generally no signs or symptoms associated with being a carrier for HMSN/ACC. However, the risk to have a child affected with HMSN/ACC is increased. Testing of reproductive partners is recommended for carriers of HMSN/ACC.

  • How common is Hereditary Motor and Sensory Neuropathy with Agenesis of the Corpus Callosum?

    HMSN/ACC is very common in the French- Canadian population of the Saguenay and Lac-St-Jean regions of Quebec. It affects 1 in 2117 newborns. This disorder is extremely rare in the general population.

  • What is analysed?

    Full gene sequencing

AFFECTED SYSTEMS
Brain
Muscle
Bones
CARRIER RATES
Ethnicity Detection Rate Carrier Frequency
General Population 90% 1 in 500