Estimating the Chance your Patient has a Child with CMMRD/BMMRD While rare, individuals with MMR mutations should be aware that if they have a child with another person who also has Lynch syndrome due to a mutation in the same gene, the child has a 25% chance of having Constitutional (or, Biallelic) Mismatch Repair Deficiency (CMMRD or BMMRD), characterized by brain, blood, gynecological, and certain pediatric cancers. The table below presents the likelihood of conceiving a child with CMMRD/BMMRD based on whether the genetic status of the parents are known or not for each MMR gene.
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| Potential Estimated Risk for CMMRD/BMMRDa
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| Gene
| Literature-based mutation frequency
| Both partners mutation status unknown | Partner 1: Lynch syndrome
Partner 2: mutation status unknown | Both partners with Lynch syndrome | Example populations with known founder mutations
| | PMS2 | 1/714 | 1/2 million | 1/2856 | 1/4 | American (Caucasian, British, Swedish, descent), Inuit,15 Norwegian | | MSH6 | 1/758 | 1/2.3 million | 1/3032 | 1/4 | Ashkenazi Jewish, Danish, Finnish, French Canadian, Dutch, Swedish | | MLH1 | 1/1946 | 1/15.1 million | 1/7746 | 1/4 | Chinese, Danish, Dutch, Finnish, French Canadian, German, Korean, Italian, Portuguese, Taiwanese | | MSH2b | 1/2841 | 1/32.3 million | 1/11,364 | 1/4 | American, Ashkenazi Jewish Canadian, Chinese, Italian, Portuguese, Spanish | | EPCAMb | Unknown | Unknown | Unknown | 1/4 | Spanish, Dutch | a If normal fertility and no embryonic lethality. b Theoretically, an MSH2 mutant allele and an EPCAM deletion that results in transcriptionally silencing of MSH2 could result in biallelic mismatch repair deficiency (BMMRD) by the resultant offspring being MSH2 null.
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