Looking to a backup gene to fight spinal muscular atrophy

Spinal muscular atrophy (SMA), a condition affecting one in every 6,000 to 10,000 children, is caused by a defect in a gene called SMN1 — which stands for “survival of motor neuron.” The defect leaves children with too little functioning SMN protein to maintain their motor neurons, which begin wasting away. Muscle strength declines and children eventually develop difficulties eating and breathing.

For Vivienne, whose name means “to live,” that meant being slow to reach motor milestones like crawling, cruising and walking as a toddler. For her parents, it meant hearing that her life expectancy would not be normal.

But a new back-door approach seems to be helping Vivienne, now in first grade, at least thus far.

As it happens, most of us carry a backup gene for SMN1 — namely SMN2. SMN2 is almost identical to SMN1, but the small letter change (a “T” rather than a “C” in the coding region known as exon 7) usually causes the entire exon 7 to be spliced out. As a result, the SMN protein that’s made is shorter and less functional.

But some people have extra copies of SMN2 and can produce more full-length SMN; the more copies, the less severe their disease. Children with type 1 SMA, the most severe form, have only one or two copies and usually die before the age of 2. Vivienne, with type 2 SMN, has three copies of SMN2. People with four or more copies can have mild disease with few symptoms, and are usually able to walk independently.

Read the full post on Vector: Rallying a backup gene could boost strength in spinal muscular atrophy

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