What does the SMN1 gene do?
The SMN1 gene provides instructions for making the survival motor neuron (SMN) protein. The SMN protein is found throughout the body, with highest levels in the spinal cord.
What is the difference between SMN1 and SMN2?
The SMN1 and SMN2 genes are more than 99 percent identical and lie within an inverted duplication on chromosome 5q13. 2 [5]. SMN1 lies telomeric of SMN2. The main difference between them is a C to T transition in exon 7 of SMN2 [9,10].
What is SMN1 gene test?
Use of test Inheritance of SMA is autosomal recessive. This test detects deletions of the SMN1 gene which cause more than 95% of cases of SMA. The result can have diagnostic and familial implications.
How many copies of SMN1 is normal?
Second, the copy number of SMN1 can vary on a chromosome; we have observed that approximately 5% of the normal population possess three copies of SMN1.
What does it mean if you have 2 copies of SMN1 gene?
If you have two copies of the healthy gene, it means that you have a reduced risk of being a carrier. If you have one healthy copy of SMN1, it means the other copy is faulty and you are a carrier. You could pass the faulty copy of the SMN1 gene to your child.
What chromosome is SMN1 on?
The most common form of SMA (types 1-4) is caused by a defect (mutation) in the SMN1 gene on chromosome 5. (People have two SMN1 genes — one on each chromosome 5). In 94% of all SMA cases, this mutation involves a deletion in a segment known as exon 7.
What does it mean to have 3 copies of SMN2?
Children with SMA type 2 generally have three copies of the SMN2 gene. 5. Muscle weakness is predominantly proximal (close to the center of the body) and involves the lower limbs more than the upper limbs. Usually, the face and the eye muscles are unaffected.
What does negative for SMN1 deletion mean?
Negative result A negative test result is characterized by the presence of detectable amounts of SMN1 exon 7, with an SMN1 exon 7 copy number of >1, with the presence of subtle intragenic point mutations within the SMN1 gene having been ruled out.
What does it mean if you have 2 copies of SMN1?
What does it mean if you have 3 copies of SMN1 gene?
In healthy individuals without a family history of SMA, detection of two SMN1 copies reduces (but does not eliminate) the risk of being a carrier, though sensitivity of detection using dosage analysis is lower among some ethnicities. Detection of 3 SMN1 copies further reduces the carrier risk.
Is SMN1 2 copies normal?
Diploid gene dose or 2 copies of SMN1 indicates normal (not affected) status, 1x gene dosage or 1 copy of the SMN1 gene most likely indicates carrier status and deletions (less than 0.1x) of SMN1 or 0 copies of the SMN1 gene designates affected status. The SMA component of this assay does not test for point mutations.
How is the SMN1 gene mutated?
(People have two SMN1 genes — one on each chromosome 5). In 94% of all SMA cases, this mutation involves a deletion in a segment known as exon 7. This area is located in the long arm of the chromosome 5, in the 5q13.