SMARD1 is a rare, autosomal, recessive motor neuron disorder that affects infants. An inherited disease, it is also known as “Distal SMA,” “Neuropathy severe infantile axonal with respiratory failure,” and “Diaphragmatic SMA.”
Diaphragmatic weakness, distal muscle atrophy, motor sensory neuropathy, and autonomic dysfunction are common characteristics of this disease.
It is a very serious disease, and life expectancy without ventilation is around 13 months.
What is Known About SMARD1?
Early involvement of the diaphragm and the predominance of distal muscle weakness distinguishes SMARD1 from Type I SMA. In type I SMA, symptoms manifest in the reverse order. Infants with SMA will have distal muscle atrophy — or atrophy in muscles a distance from the body’s core — before respiratory failure.2
Researchers identified mutations in the gene encoding an enzyme known as immunoglobulin mu binding protein 2 (IGHMBP2), located on chromosome 11q13. IGHMBP2 is a ribosome-associated helicase that unwinds RNA and DNA duplicates in vitro.3 SMARD1 is not linked to the SMN1 gene locus on chromosome 5q13. These mutations lead to the production of defective protein causing degeneration of alpha-motor neurons.1
Infants with atypical SMA should be tested for SMARD1. Parents who are also blood relatives (consanguineous parents) and who had a child with sudden infant death syndrome should also be examined for this mutation.
Besides SMARD1, there are other 4 forms of the disease with a later onset (SMARD2, SMARD3, SMARD4 and SMARD5).4 The mutations appear on different genes and chromosomes.
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