Homozygosity for CHEK2 p.Gly167Arg leads to a unique cancer syndrome with multiple complex chromosomal translocations in peripheral blood karyotype.

BACKGROUND: Chromosomal instability, as reflected by structural or copy-number changes, is a known cancer characteristic but are rarely observed in healthy tissue. Mutations in DNA repair genes disrupt the maintenance of DNA integrity and predispose to hereditary cancer syndromes. OBJECTIVE: To clinically characterise and genetically diagnose two reportedly unrelated patients with unique cancer syndromes, including multiorgan tumourogenesis (patient 1) and early-onset acute myeloid leukaemia (patient 2), both displaying unique peripheral blood karyotypes. METHODS: Genetic analysis in patient 1 included TruSight One panel and whole-exome sequencing, while patient 2 was diagnosed by FoundationOne Heme genomic analysis; Sanger sequencing was used for mutation confirmation in both patients. Karyotype analysis was performed on peripheral blood, bone marrow and other available tissues. RESULTS: Both patients were found homozygous for CHEK2 c.499G>A; p.Gly167Arg and exhibited multiple different chromosomal translocations in 30%-60% peripheral blood lymphocytes. This karyotype phenotype was not observed in other tested tissues or in an ovarian cancer patient with a different homozygous missense mutation in CHEK2 (c.1283C>T; p.Ser428Phe). CONCLUSIONS: The multiple chromosomal translocations in patient lymphocytes highlight the role of CHK2 in DNA repair. We suggest that homozygosity for p.Gly167Arg increases patients' susceptibility to non-accurate correction of DNA breaks and possibly explains their increased susceptibility to either multiple primary tumours during their lifetime or early-onset tumourigenesis.

A nonsense mutation in the human homolog of Drosophila rogdi causes Kohlschutter-Tonz syndrome.

Kohlschutter-Tonz syndrome (KTS) is a rare autosomal-recessive disorder of childhood onset, and it is characterized by global developmental delay, spasticity, epilepsy, and amelogenesis imperfecta. In 12 KTS-affected individuals from a Druze village in northern Israel, homozygosity mapping localized the gene linked to the disease to a 586,513 bp region (with a LOD score of 6.4) in chromosomal region 16p13.3. Sequencing of genes (from genomic DNA of an affected individual) in the linked region revealed chr16: 4,848,632 G>A, which corresponds to ROGDI c.469C>T (p.Arg157(∗)). The nonsense mutation was homozygous in all affected individuals, heterozygous in 10 of 100 unaffected individuals from the same Druze community, and absent from Druze controls from elsewhere. Wild-type ROGDI localizes to the nuclear envelope; ROGDI was not detectable in cells of affected individuals. All affected individuals suffered seizures, were unable to speak, and had amelogenesis imperfecta. However, age of onset and the severity of mental and motor handicaps and that of convulsions varied among affected individuals homozygous for the same nonsense allele.