Constitutional mismatch repair deficiency and childhood leukemia/lymphoma--report on a novel biallelic MSH6 mutation

Abstract

Biallelic mutations of mismatch repair genes cause constitutional mismatch repair deficiency associated with an increased risk for childhood leukemia/lymphoma. We report on a case with constitutional mismatch repair deficiency caused by a novel MSH6 mutation leading to a T-cell lymphoma and colonic adenocarcinoma at six and 13 years of age, respectively. A review of the literature on hematologic malignancies in constitutional mismatch repair deficiency showed that in almost half of the 47 known constitutional mismatch repair deficiency families, at least one individual is affected by a hematologic malignancy, predominantly T-cell lymphomas. However, diagnosing constitutional mismatch repair deficiency may be difficult when the first child is affected by leukemia/lymphoma, but identification of the causative germline mutation is of vital importance: (i) to identify relatives at risk and exclude an increased risk in non-mutation carriers; (ii) to prevent hematopoietic stem cell transplantation from sibling donors also carrying a biallelic germline mutation; and (iii) to implement effective surveillance programs for mutation carriers, that may reduce constitutional mismatch repair deficiency-associated mortality.

Figure 1.

Pedigree of the family investigated. Roman numerals (I–V), generations; circles, females; squares, males; numbers above the symbol, individual identifier; numbers below the symbol, age at diagnosis of colorectal cancer (diseased individuals) or age (healthy individuals); black symbol, patient with childhood T-NHL at the age of six, T-NHL relapse at the age of eight, and colorectal cancer at the age of 13; gray symbol, diseased uncle with synchronous colorectal cancer; +/+, wild-type; +/−, heterozygous carrier, −/−, homozygous carrier of the identified frameshift mutation in MSH6 (c.691delG, p.Val231TyrfsX15).

Figure 2.

Immunohistochemistry and molecular analyses in family members. (A) Immunohistochemical analysis of colorectal cancer of our patient (V:10). While MSH2, MLH1 and PMS2 staining were inconspicuous (data not shown), a loss of MSH6 was seen in malignant and non-malignant colonic mucosa in comparison to a control. In contrast, following HSCT, lymphocytes infiltrating the colonic mucosa show nuclear staining for MSH6 (NBT/BCIP staining, 100x magnification). (B) Direct sequencing of MSH6 (NM_000179) identified a novel frameshift mutation in exon 4: c.691delG, p.Val231TyrfsX15. The electropherograms represent an example of two independent sequence analyses. Black arrows indicate the G in the wild-type sequence that is deleted in one or both alleles in the case of a monoallelic or biallelic mutation, respectively. (C) Allele-specific PCR. Using a specific forward primer for the wild-type or mutant allele, results of direct sequencing were confirmed by allele-specific PCR. DNA was extracted from peripheral blood cells of the parents (IV:9, IV:8) and their siblings (IV:7, IV:10). To access DNA of our patient prior to HSCT, DNA was extracted from a formalin-fixed paraffin-embedded lymph node without any evidence of malignancy. WT, wild-type control; L, molecular marker.

Figure 3.

Molecular cause of LS and CMMRD. Relative distribution of causative mutations in MLH1, MSH2, MSH6 and PMS2 in LS and CMMRD indicating the predominance of mutations MLH1 and MSH2, and MSH6 and PMS2 in LS and CMMRD, respectively.