MLH1 and Lynch syndrome: Inherited mismatch repair defects can be seen in Lynch syndrome, which is characterized by autosomal dominant inheritance of heterozygous pathogenic germline mutations in one of the MMR genes (MLH1, MSH2, MSH6, or PMS2) [7]; in Lynch-like syndrome, which results from double somatic mutations in one of the MMR genes; and in constitutional MMR deficiency syndrome (CMMRD), an autosomal recessive disorder caused by biallelic pathogenic germline mutations in MMR genes [8].