Mosaic Variegated Aneuploidy syndrome 2 caused by biallelic variants in CEP57, two new cases and review of the phenotype

Mosaic variegated aneuploidy syndrome 2 with biallelic novel CEP57 splice site variation in Indian siblings: Expanding the clinical and molecular spectrum

Mosaic variegated aneuploidy syndrome 2 (MVA2) (MIM# 614114) is a rare autosomal recessive condition caused by biallelic loss of function variants in the CEP57 gene. MVA2 is characterized by a variable phenotype ranging from poor growth to facial dysmorphism, short stature and congenital heart defects. Only 11 families and 5 pathogenic variants of MVA2 have been described so far. Intragenic duplication of 11 nucleotides (c.915_925dup11) in homozygous or compound heterozygous state is the commonest genetic aberration (10/13). We describe the first Indian family with two siblings with a novel homozygous splice site variant (c.382+2T>C) in CEP57. Molecular characterization demonstrated skipping of exon 3 due to the variant with protein modeling predicting subsequent complete loss of function. This is the first report of a splice site variation in CEP57 leading to MVA2.

Biallelic germline mutations in MAD1L1 induce a syndrome of aneuploidy with high tumor susceptibility

Germline mutations leading to aneuploidy are rare, and their tumor-promoting properties are mostly unknown at the molecular level. We report here novel germline biallelic mutations in MAD1L1, encoding the spindle assembly checkpoint (SAC) protein MAD1, in a 36-year-old female with a dozen of neoplasias. Functional studies demonstrated lack of full-length protein and deficient SAC response, resulting in ~30 to 40% of aneuploid blood cells. Single-cell RNA analysis identified mitochondrial stress accompanied by systemic inflammation with enhanced interferon and NFκB signaling both in aneuploid and euploid cells, suggesting a non-cell autonomous response. MAD1L1 mutations resulted in specific clonal expansions of γδ T cells with chromosome 18 gains and enhanced cytotoxic profile as well as intermediate B cells with chromosome 12 gains and transcriptomic signatures characteristic of leukemia cells. These data point to MAD1L1 mutations as the cause of a new variant of mosaic variegated aneuploidy with systemic inflammation and unprecedented tumor susceptibility.

A novel CEP57 variant associated with mosaic variegated aneuploidy syndrome in a Chinese female presenting with short stature, microcephaly, brachydactyly, and small teeth

Background

Mosaic variegated aneuploidy (MVA) syndrome is a rare, autosomal recessive genetic disease. Here, we report an ultra‐rare case of MVA syndrome associated with a CEP57 variant.

Methods

We retrospectively analyzed the clinical data of a 9‐year‐old female patient and surveyed her family members. Whole‐exome sequencing and karyotype analysis were performed; suspected mutations were verified using Sanger sequencing.

Results

The patient presented with intrauterine growth restriction, short stature, microcephaly, facial dysmorphism, brachydactyly, and small teeth, and she showed unsatisfactory response to GH replacement therapy. Laboratory tests revealed high insulin‐like growth factor‐1 levels. Karyotype analysis of the peripheral blood showed mosaic variegated aneuploidies. Whole‐exome and Sanger sequencing revealed a novel homozygous nonsense variant, NM_014679.4: c.312 T > G, in CEP57 that leads to translation termination (p.Tyr104*). The parents were heterozygous carriers of the identified variant.

Conclusion

This study presents an ultra‐rare case of CEP57‐driven MVA syndrome, identifying a novel homozygous nonsense variant of CEP57 (p.Tyr104*). Our findings enrich the CEP57 mutational spectrum and emphasize the importance of genetic testing in patients with microcephaly and short stature. Furthermore, we conclude that growth hormone treatment is ineffective in such patients.