premutation

adj

1. (not-comparable)Of or relating to a premutation.

   “Fragile X syndrome is caused by mutations in the FMR1-gene, which is characterized by an expansion of a CGG triplet in the 5’ UTR. Normal individuals have 6–44 CGG repeats, while carriers of gray zone or premutation alleles have 45–54 and 55–200 repeats, respectively.”

noun

1. A nucleotide sequence variation that is not enough to be classed as a mutation (for example, does not affect protein expression enough to produce clinical symptoms) but nonetheless represents an unusual variant that is predisposed to still greater variation in future cell divisions (that is, predisposed to leading to a mutation).