The hMLH1 (human mutL homolog 1) gene is located on chromosome 3 (3p21.3). It is composed of 19 exons spanning a region of 57360 bp.The DNA mismatch repair protein Mlh1 becomes active in the presence of ATP when it is paired with another protein made from the PMS2 gene. This active protein complex coordinates the binding of various other proteins that repair mistakes made during DNA replication. The MLH1 gene is a member of a set of genes known as the mismatch repair (MMR) genes.

Defects in MLH1 are the cause of hereditary non-polyposis colorectal cancer type 2 (HNPCC2). Mutations in more than one gene locus can be involved alone or in combination in the production of the HNPCC phenotype (also called Lynch syndrome). HNPCC is reported to be the most common form of inherited colorectal cancer in the Western world, and accounts for 15% of all colon cancers.

In addition, the hMLH1 gene is inactivated by promoter hypermethylation (10-20%) in a number of different cancers, such as colon, endometrial and gastric cancers. The hypermethylation is almost always associated with microsatellite instability and, in cell lines, mismatch repair deficiency.

PyroMark MLH1 assay detects the level of methylation in a region -209 to -188 from transcription start site (Ensembl gene: ENSG00000076242).

Illustration of Pyromark MLH1 assay results. The upper pyrogram shows results from a normal blood DNA sample and the lower pyrogram frim an in vitro methylated DNA sample. Orange columns indicate the measured CpG sites. Blue columns indicate QC for completion of the bisulfite treatment (a C followed by an A in the original sequence).