Understanding your genotype for MTHFR

Recently I discovered you can be homozygous for both 677 and 1298.

Apparently, you can be any one of these possible, common, combinations:

• Normal/Normal for both 677 and 1298
• Heterozygous 1298 / Normal 677 (i.e. one parent passed down a single 1298 mutation)
• Homozygous 1298 / Normal 677 (i.e. both parents passed down the 1298 mutation)
• Heterozygous 677 / Normal 1298 (i.e. one parent passed down a single 677 mutation)
• Homozygous 677 / Normal 1298 (i.e. both parents passed down the 677 mutation)
• Heterozygous 677 / Homozygous 1298 (one parent passed down the 677 mutation; both passed down the 1298 mutation)
• Homozygous 677 / Heterozygous 1298 (both parents passed down the 677 mutation; one passed down the 1298 mutation)
• Heterozygous 677 / Heterozygous 1298 (Compound Heterozygous: one parent passed 677; one passed 1298 mutation)
• Homozygous 677 / Homozygous 1298 (Compound Homozygous, meaning you have two 677, two 1298 mutation)

Deciphering  genotype for MTHFR C677T

CC = a normal C677T MTHFR gene
CT = a heterozygous mutation which is one mutation of C677T
TT = a homozygous mutation which is two mutations of C677T

Deciphering  genotype for MTHFR A1298C

AA = a normal A1298C MTHFR gene
AC = a heterozygous mutation which is one mutation of A1298C
CC = a homozgyous mutation which is two mutations of A1298C

MTHFR 677CT + MTHFR 1298AC = a compound heterozygous mutation which is one mutation from two different parts of the gene.

MTHFR 677TT + MTHFR 1298CC = a compound homozygous mutation which is two mutations from two different parts of the gene.