In a recent review, CMMR-D and Lynch syndrome are reviewed (JPGN 2014; 58: 144-52). The term CMMR-D refers to constitutional mismatch repair deficiency.  This occurs when an individual inherits two MMR gene defects (rather than one gene defect in Lynch syndrome). CMMR-D can occur when a different mutation is inherited from each parent. MMR genes include MLH1, MSH2, MSH6 and PMS2.

Unlike Lynch syndrome when screening for colorectal cancer (CRC) usually starts at age 20 years or 5 years before first CRC in family, with CMMR-D screening recommendations include yearly endoscopic evaluation beginning at age 3 years or at diagnosis.  Complete management guidelines are listed in Table 4.