What does it mean? My genetic test says -/- +/- or +/+
There are three possible results for every SNP.
A given Single Nucleotide Polymorphism SNP (gene variant: “mutation”) may occur in one or both copies of the gene. If found in only one copy, you are heterozygous (-/+) for the mutation.
If the SNP occurs in both copies, you are homozygous (+/+) for the mutation.
If there is no mutation, you are “wild type” (-/-): this is also the most common in the population.
Why do we have two copies of each gene?
Our genetic code is located on our chromosomes, and we have 23 pairs of chromosomes (the 23rd pair is either XX for women or XY for men). Each gene is coded twice, with one code located on both chromosomes of your pair.
For example, MTHFR C677T is located on chromosome 1; since we have in each of our cells a pair of chromosome 1, we carry two copies of each gene.
A homozygous genotype can have more significant health implications compared to the milder heterozygous genotype.
For example, the C677T mutation in MTHFR reduces enzyme function by 75% and 35% in homozygous and heterozygous genotypes, respectively.
A 50% or 75% reduction of the activity of the enzyme coded by the gene is significant enough to impact your health even if you are perfectly healthy.