Constitutional mismatch repair deficiency in childhood colorectal cancer harboring a de novo variant in the MSH6 gene: a case report.

Constitutional mismatch repair deficiency (CMMRD) is caused by biallelic pathogenic variants in one of the mismatch repair genes, and results in early onset colorectal cancer, leukemia, brain tumors and other childhood malignancies. Here we report a case of CMMRD with compound heterozygous variants in the MSH6 gene, including a de novo variant in multiple colorectal cancers. An 11-year-old girl, who presented with multiple spots resembling café-au-lait macules since birth, developed abdominal pain, diarrhea and bloody stool over two months. Colonoscopy revealed multiple colonic polyps, including a large epithelial tumor, and pathological examination revealed tubular adenocarcinoma. Brain magnetic resonance imaging (MRI) showed an unidentified bright object (UBO), commonly seen in neurofibromatosis type 1 (NF1). Genetic testing revealed compound heterozygous variants, c. [2969T > A (p.Leu990*)] and [3064G > T (p.Glu1022*)] in the MSH6 gene; c.2969T > A (p.Leu990*) was identified as a de novo variant. We present the first report of a CMMRD patient with a de novo variant in MSH6, who developed colorectal cancer in childhood. CMMRD symptoms often resemble NF1, as observed here. Physicians should become familiar with CMMRD clinical phenotypes for the screening and early detection of cancer.

Citation

Keinosuke Hizuka, Shin-Ichiro Hagiwara, Takatoshi Maeyama, Hitoshi Honma, Masanobu Kawai, Kiwamu Akagi, Michiko Yasuhara, Naohiro Tomita, Yuri Etani. Constitutional mismatch repair deficiency in childhood colorectal cancer harboring a de novo variant in the MSH6 gene: a case report. BMC gastroenterology. 2021 Feb 10;21(1):60

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PMID: 33568103

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