Haplotype analysis suggest that the MLH1 c.2059C > T mutation is a Swedish founder mutation

Genomic Medicine in the Developing World: Cancer Spectrum, Cumulative Risk and Survival Outcomes for Lynch Syndrome Variant Heterozygotes with Germline Pathogenic Variants in the MLH1 and MSH2 Genes

Background: Although genetic testing has improved our ability to diagnose Lynch syndrome (LS), there is still limited information on the extent of variations in the clinical and genetic landscape among LS variant heterozygotes (LSVH) in Africa. We sought to investigate the cancer spectrum, cumulative risk, and survival outcomes of LSVH with pathogenic/likely pathogenic variants (P/LPVs) in the MLH1 and MSH2 genes using a LS registry in South Africa over the last 30 years. Methods: A retrospective study was conducted to retrieve demographic, clinical, and genetic data of all LSVH with P/LPVs in the MLH1 and MSH2 genes from our LS registry. Genetic data were analyzed according to cancer spectrum, cumulative risk, and crude survival. We used the Chi-squared and t-test to assess differences between groups, and Kaplan-Meier survival analyses were used to analyze the cumulative risk and crude survival outcomes. A p-value < 0.05 at a 95% confidence interval was considered statistically significant. Results: We analyzed a total of 577 LSVH from 109 families. About 450 (78%) and 127 (22%) LSVH harbored a disease-causing mutation in MLH1 and MSH2, respectively. A South African founder PV (MLH1:c.1528C>T) accounted for 74% (n = 426) of all LSVH. CRC was the most common diagnosed cancer in both MLH1 and MSH2 LSVH. MLH1 LSVH had a younger age at cancer diagnosis than MSH2 LSVH (43 vs. 47 years, respectively, p = 0.015). Extracolonic cancers were predominantly higher in female LSVH (n = 33, 35%) than in male LSVH (n = 8, 7%) with the MLH1:c.1528C>T founder PV. The cumulative risk of any cancer and CRC at any age was higher in MLH1 LSVH than in MSH2 LSVH (p = 0.020 and p = 0.036, respectively). LSVH with the MLH1:c.1528C>T PV had a better 10-year overall survival after the first cancer diagnosis, particularly for CRC. Conclusions: LSVH with P/LPVs in the MLH1 and MSH2 genes exhibited significant gene- and sex-specific differences in cancer spectrum, cumulative risk and survival outcomes. Cancer risk and survival estimates described in this study can be used to guide surveillance and genetic counselling for LSVH in our population.

Haplotype analysis detects MLH1 founder variant in Indian Lynch syndrome patient cohort

Lynch syndrome (LS) is an autosomal dominant hereditary cancer predisposition syndrome whereby the lifetime risk of developing gastrointestinal and genitourinary cancers rises by to over 50%. It is caused by heterozygous variants in the DNA mismatch repair genes- MLH1, MSH2, MSH6 and PMS2, with the majority detected in MLH1 and MSH2. Recurrently observed LS-associated variants in apparently unrelated individuals have either arisen de novo in different families due to mutation hotspots or are inherited from a common ancestor (founder) that lived several generations back. Testing for founder variants can facilitate molecular diagnosis of LS more efficiently and cost effectively than screening for all possible variants in the MMR genes. Here, we report a study of the missense variant c.306G > T in the MLH1 gene, the first potential founder variant identified in LS patients of Indian ethnicity. Haplotype analysis consisting of 25 LS carriers with the MLH1 c.306G > T variant and 100 healthy controls confirmed a shared haplotype in cases spanning a 27.8 kb region encompassing the c.306G > T variant (𝝌2 = 96.418; p = < 0.0001). Age of variant analysis suggests the variant to have arisen in the population approximately 800 years (95% CI: 670-934 years) ago. Furthermore, it is estimated that c.306G > T variant is likely to be observed in 6.4% of all LS patients of Indian ethnicity. These findings have important implications for genetic counselling and molecular diagnosis of Lynch syndrome.

Clinical and genetic features of a large homogeneous cohort of oculopharyngeal muscular dystrophy patients from the Canary Islands

BACKGROUND

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant, late-onset myopathy characterized by ptosis, dysphagia, and progressive proximal limb muscle weakness. The disease is produced by a short expansion of the (GCN)_n triplet in the PABPN1 gene. The size of expansion has been correlated to the disease onset and severity. We report the clinical features of a large cohort of OPMD patients harboring the (GCN)15 allele from the Canary Islands.

METHODS

A retrospective observational study was performed analyzing the clinical, demographic, and genetic data of 123 OPMD patients. Clinical data from this cohort were compared with clinical data collected in a large European study including 139 OPMD patients.

RESULTS

A total of 113 patients (94.2%) carried the (GCN)15 expanded PABN1 allele. Age of symptoms' onset was 45.1 years. The most frequent symptom at onset was ptosis (85.2%) followed by dysphagia (12%). The severity of the disease was milder in the Canary cohort compared to European patients as limb weakness (35.1% vs. 50.4%), the proportion of patients that require assistance for walking or use a wheelchair (9.3% vs. 27.4%), and needed of surgery because of severe dysphagia (4.6% vs. 22.8%) was higher in the European cohort.

CONCLUSIONS

Nearly 95% of patients with OPMD from the Canary Islands harbored the (GCN)15 expanded allele supporting a potential founder effect. Disease progression seemed to be milder in the (GCN)15 OPMD Canary cohort than in other cohorts with shorter expansions suggesting that other factors, apart from the expansion size, could be involved in the progression of the disease.

Prevalence of CNV-neutral structural genomic rearrangements in MLH1, MSH2, and PMS2 not detectable in routine NGS diagnostics

Routine diagnostics for colorectal cancer patients suspected of having Lynch-Syndrome (LS) currently uses Next-Generation-Sequencing (NGS) of targeted regions within the DNA mismatch repair (MMR) genes. This analysis can reliably detect nucleotide alterations and copy-number variations (CNVs); however, CNV-neutral rearrangements comprising gene inversions or large intronic insertions remain undetected because their breakpoints are usually not covered. As several founder mutations exist for LS, we established PCR-based screening methods for five known rearrangements in MLH1, MSH2, or PMS2, and investigated their prevalence in 98 German patients with suspicion of LS without a causative germline variant or CNV detectable in the four MMR genes. We found no recurrence of CNV-neutral structural rearrangements previously described: Neither for two inversions in MLH1 (exon 1 and exon 16-19) within 33 MLH1-deficient patients, nor for two inversions in MSH2 (exon 1-7 and exon 2-6) within 48 MSH2-deficient patients. The PMS2 insertion in intron 7 was detected in one of 17 PMS2-deficient patients. None of the four genomic inversions constitutes a founder event within the German population, but we advise to test the rare cases with unsolved PMS2-deficiency upon the known insertion. As a next diagnostic step, tumour tissue of the unsolved patients should be sequenced for somatic variants, and germline analysis of additional genes with an overlapping clinical phenotype should be considered. Alternatively, full-length cDNA analyses may detect concealed MMR-defects in cases with family history.

Advances in Identification of Susceptibility Gene Defects of Hereditary Colorectal Cancer

Colorectal cancer (CRC) is a common malignant tumor of the digestive system worldwide, associated with hereditary genetic features. CRC with a Mendelian genetic predisposition accounts for approximately 5-10% of total CRC cases, mainly caused by a single germline mutation of a CRC susceptibility gene. The main subtypes of hereditary CRC are hereditary non-polyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP). With the rapid development of genetic testing methods, especially next-generation sequencing technology, multiple genes have now been confirmed to be pathogenic, including DNA repair or DNA mismatch repair genes such as APC, MLH1, and MSH2. Since familial CRC patients have poor clinical outcomes, timely clinical diagnosis and mutation screening of susceptibility genes will aid clinicians in establishing appropriate risk assessment and treatment interventions at a personal level. Here, we systematically summarize the susceptibility genes identified to date and the potential pathogenic mechanism of HNPCC and FAP development. Moreover, clinical recommendations for susceptibility gene screening, diagnosis, and treatment of HNPCC and FAP are discussed.