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| SPECIALIST ANSWERS
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Question |
I have a child 5 yr with progressive muscle weakness begining with frequent falls initially and now not able to walk. this hAS happenned over 2-3 years. no history of convulsions. mentally normal. non consanguinous marriage. fits in sma but the genetic study i.e SMN gene and the NAIP gene are normal. can we have sma with these genes normal. sachin d
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Answer |
SMN gene is (Survival of Motor Neurons) located on long arm of chromosome 5 (5q). In addition to the SMN gene, a copy of the SMN gene is present on 5q, located centromeric to the SMN gene.
SMNt stands for telomeric or SMN1 is mutated to cause SMA
SMNc stands for centromeric or SMN2 may alter severity of SMA.
Deletion of exon 7 or 7 & 8 is associated with SMA.
94% of SMA patients have deletion of
exon 7 from both of their SMN1 genes. 6% of SMA patients have an exon 7 deletion on one SMN1 gene copy and a small mutation on the second SMN1 copy.
Rarely, SMA patients may have non-deletion mutations on both SMN1 gene copies.
SMR gene testing is done by PCR. However it has its limitations. It is positive for only 94% of individuals with SMA and 6% of patients with SMA may have normal tests.
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