What does it mean to have 2 copies of SMN1?
What does it mean to have 2 copies of SMN1?
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.
Is 3 copies of SMN1 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. It is therefore possible for a carrier to possess one chromosome with two copies and a second chromosome with zero copies.
What does 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.
How common is it to be a carrier of a genetic disorder?
It is estimated that everyone is a carrier of around half a dozen rare recessive genetic mutations Structural changes in a gene – they can be alterations to a gene’s size, arrangement, or molecular sequence. that could lead to disease – this is actually normal and not something to be uncomfortable about.
How do I know if I’m a carrier of SMA?
Carrier Testing A DNA test is the only way to know if a person is a carrier of SMA. The DNA test is a simple procedure, based on a blood test. In the general population, this test can detect about 95% of carriers. However, in African-American populations, detection is closer to 70%.
What happens if you have two copies of the SMN1 gene?
In individuals found to have two copies of SMN1, the test cannot determine whether those copies are on the same [2+0] or opposite [1+1] chromosomes. This impacts the sensitivity of carrier screening. In the case of a two-copy allele, the individual is a “silent carrier” and has a risk of passing on an allele that is deleted for SMN1.
How many copies of SMN1 do you have?
Most people have two copies of the SMN1 gene. SMA occurs when both of an individual’s SMN1 copies are missing or mutated. Except in very rare cases, this happens when that individual has inherited two faulty copies of the gene—one from each parent. These parents do not have SMA themselves but are said to be “carriers” of SMA.
How is SMN1 gene sequencing used to diagnose spinal muscular atrophy?
Among patients with clinical presentations suggestive of SMA, detection of zero SMN1 copies confirms the diagnosis. In symptomatic patients with one SMN1 copy, SMN1 gene sequencing should be considered to identify the small percentage of patients with heterozygous sequence variants or small deletions.
How many people are heterozygous for SMN1?
Of the remaining 5%, most are heterozygous for a deletion of SMN1 on one chromosome and a small pathogenic, or disease-causing, variant in the SMN1 copy on the other chromosome [0+1 d] (Wirth 2000). SMN1 copy number varies among healthy individuals [1+1 or 2+1].