Genetic notations

Question

Genetic testing revealed these two mutations (hypothetically):

IVS11+6G>A and IVS11-4G＞A

Could you please explain every part of this notation, especially "+" and "-" signs.

Answer 1

These describe mutations (SNPs) in introns.

IVS stands for intervening sequence (which is another term for intron).

The number following IVS specifies which intron the mutation occurs in (intron 1 follows exon 1, etc).

The +n or -n, where n is an integer, gives the location of the nucleotide. +n counts 3' from the preceding exon whereas -n counts 5' from the following exon. I think that the first and last nucleotide of each exon is given position 0 such that, for example, +1 refers to the first nucleotide of the intron and -1 refers to the last.

X>Y, where X and Y are nucleotides, describe what mutation has occurred.

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IVS11+6G>A means a G to A transition at position +6 of intron 11

IVS11-4G＞A means a G to A transition at position -4 of intron 11