The Prevalence and Molecular Landscape of Lynch Syndrome in the Affected and General Population.

BACKGROUND: Lynch syndrome (LS) is the most frequent genetically pre-disposed colorectal cancer (CRC) syndrome, accounting for 2-3% of all CRC cases. In Estonia, ~1000 new cases are diagnosed each year. This retroactive and prospective study aimed to estimate the prevalence of LS and describe disease-causing variants in mismatch repair (MMR) genes in a diagnostic setting and in the Estonian general population. METHODS: LS data for the diagnostic cohort were gathered from 2012 to 2022 and data for the general population were acquired from the Estonian Biobank (EstBB). Furthermore, we conducted a pilot study to estimate the improvement of LS diagnostic yield by raising the age limit to >50 years for immunohistochemistry analysis of MMR genes. RESULTS: We estimated LS live birth prevalence between 1930 and 2003 in Estonia at 1:8638 (95% CI: 1: 9859-7588). During the study period, we gathered 181 LS individuals. We saw almost a six-fold increase in case prevalence, probably deriving from better health awareness, improved diagnostic possibilities and the implementation of MMR IHC testing in a broader age group. CONCLUSION: The most common genes affected in the diagnostic and EstBB cohorts were MLH1 and PMS2 genes, respectively. The LS diagnosis mean age was 44.8 years for index cases and 36.8 years (p = 0.003) for family members. In the MMR IHC pilot study, 29% had LS.

The prevalence of germline pathogenic variants in Estonian colorectal cancer patients: results from routine clinical setting 2016-2021.

Background: Colorectal cancer (CRC) is the third most common cancer in Estonia in both women and men. According to the Estonian National Institute for Health Development, in 2017, there were 357 new colon cancer only cases in women and 282 in men. For colorectal cancer, the number for men and women altogether was 1040 in the same year. In 2018, there were over 1.8 million new cases worldwide. The Mayo Clinic found in a prospective, two-year multi-site study of CRC patients that 15.5% of patients carried pathogenic germline variants (PGV), using an >80 gene Next Generation Sequencing (NGS) panel. Material and methods: This retrospective study aimed to analyse the estimated prevalence of pathogenic/likely pathogenic germline variants in Estonian colorectal cancer patients using NGS in a routine clinical setting. We gathered five-year data (July 2016-July 2021) of colorectal cancer patients (mostly not selected for age or family history) tested with either Illumina TruSight Cancer (94 genes) or TruSight Hereditary Cancer (113 genes) NGS panels. Results: Three hundred and fourteen NGS analyses were performed due to either CRC or polyposis in anamnesis and/or family anamnesis, including 126 CRC cases and 44 colorectal polyposis cases, while 144 were either healthy family members or had other types of cancers. While a known disease-causing variant was identified in 16.4% of all cancer patients tested, we found that 21.4% of CRC patients had such a variant. Among the 44 colorectal polyps cases MLH1, gene was the most affected one (25%), the second and third most affected genes were MSH2 and CHEK2. Other genes with disease-causing variants found in CRC patients included APC, BLM, BMPR1A, BRCA1, FANCM, MSH6, MUTYH, PMS2, SMAD4, SPINK1 and VHL. Conclusion: Our result give an overview of genetic testing of CRC patients, the prevalence of disease-causing variants and their landscape in Estonia. According to Estonian data, only 2.7-6.1% of CRC patients are genetically tested, which is around ten times less frequently than breast cancer patients and their family members. The diagnostic yield of CRC patients is 21.4%, suggesting that genetic testing will likely improve timely diagnosis and outcomes.

Effectiveness of whole exome sequencing in unsolved patients with a clinical suspicion of a mitochondrial disorder in Estonia.

OBJECTIVE: Reaching a genetic diagnosis of mitochondrial disorders (MDs) is challenging due to their broad phenotypic and genotypic heterogeneity. However, there is growing evidence that the use of whole exome sequencing (WES) for diagnosing patients with a clinical suspicion of an MD is effective (39-60%). We aimed to study the effectiveness of WES in clinical practice in Estonia, in patients with an unsolved, but suspected MD. We also show our first results of mtDNA analysis obtained from standard WES reads. METHODS: Retrospective cases were selected from a database of 181 patients whose fibroblast cell cultures had been stored from 2003 to 2013. Prospective cases were selected during the period of 2014-2016 from patients referred to a clinical geneticist in whom an MD was suspected. We scored each patient according to the mitochondrial disease criteria (MDC) (Morava et al., 2006) after re-evaluation of their clinical data, and then performed WES analysis. RESULTS: A total of 28 patients were selected to the study group. A disease-causing variant was found in 16 patients (57%) using WES. An MD was diagnosed in four patients (14%), with variants in the SLC25A4, POLG, SPATA5, and NDUFB11 genes. Other variants found were associated with a neuromuscular disease (SMN1, MYH2, and LMNA genes), neurodegenerative disorder (TSPOAP1, CACNA1A, ALS2, and SCN2A genes), multisystemic disease (EPG5, NKX1-2, ATRX, and ABCC6 genes), and one in an isolated cardiomyopathy causing gene (MYBPC3). The mtDNA point mutation was found in the MT-ATP6 gene of one patient upon mtDNA analysis. CONCLUSIONS: The diagnostic yield of WES in our cohort was 57%, proving to be a very good effectiveness. However, MDs were found in only 14% of the patients. We suggest WES analysis as a first-tier method in clinical genetic practice for children with any multisystem, neurological, and/or neuromuscular problem, as nuclear DNA variants are more common in children with MDs; a large number of patients harbor disease-causing variants in genes other than the mitochondria-related ones, and the clinical presentation might not always point towards an MD. We have also successfully conducted analysis of mtDNA from standard WES reads, providing further evidence that this method could be routinely used in the future.

Biallelic CACNA1A mutations cause early onset epileptic encephalopathy with progressive cerebral, cerebellar, and optic nerve atrophy.

The CACNA1A gene encodes the transmembrane pore-forming alpha-1A subunit of the Cav 2.1 P/Q-type voltage-gated calcium channel. Several heterozygous mutations within this gene, including nonsense mutations, missense mutations, and expansion of cytosine-adenine-guanine repeats, are known to cause three allelic autosomal dominant conditions-episodic ataxia type 2, familial hemiplegic migraine type 1, and spinocerebellar ataxia type 6. An association with epilepsy and CACNA1A mutations has also been described. However, the link with epileptic encephalopathies has emerged only recently. Here we describe two patients, sister and brother, with compound heterozygous mutations in CACNA1A. Exome sequencing detected biallelic mutations in CACNA1A: A missense mutation c.4315T>A (p.Trp1439Arg) in exon 27, and a seven base pair deletion c.472_478delGCCTTCC (p.Ala158Thrfs*6) in exon 3. Both patients were normal at birth, but developed daily recurrent seizures in early infancy with concomitant extreme muscular hypotonia, hypokinesia, and global developmental delay. The brain MRI images showed progressive cerebral, cerebellar, and optic nerve atrophy. At the age of 5, both patients were blind and bedridden with a profound developmental delay. The elder sister died at that age. Their parents and two siblings were heterozygotes for one of those pathogenic mutations and expressed a milder phenotype. Both of them have intellectual disability and in addition the mother has adult onset cerebellar ataxia with a slowly progressive cerebellar atrophy. Compound heterozygous mutations in the CACNA1A gene presumably cause early onset epileptic encephalopathy, and progressive cerebral, cerebellar and optic nerve atrophy with reduced lifespan. © 2016 Wiley Periodicals, Inc.