under the name constitutional mismatch repair-deficiency, (cmmr-d), it has been mapped to mlh1, msh2, msh6 or pms2. monoallelic mutations of these genes are observed in the condition known as lynch syndrome or hereditary nonpolyposis colorectal cancer, while biallelic mutations are observed in cmmr-d. people expressing the hnpcc (which itself is considered autosomal dominant) trait are considered carriers of cmmr-d, thus cmmr-d is classified as autosomal recessive.