BACKGROUND AND OBJECTIVES. Rod-Cone Dystrophies (RCDs) are genetically determined retinal dystrophies, resulting in nyctalopia, visual field progressive reduction and visual acuity decay in the late stages. Retinitis Pigmentosa (RP) is the most described type. All modes of transmission can be identified in RP, with the autosomal dominant form (ADRP) accounting for about 20% of cases. To date, over 30 genes have been related to ADRP, with RP1 gene estimated to be involved in 5-10% of cases. In a cohort of patients affected by RCD and sharing the same geographic origin from Palermo province in Western Sicily, we identified a prevalent causative variant in the RP1 gene (NM_006269.2; c.2219C>G, p.Ser740*). Objective of our study was to analyse clinical and molecular data of this population and define the entity and the meaning of this finding. MATERIALS AND METHODS. Eighty-four patients with a diagnosis of RCD or RP underwent deep phenotyping, pedigree definition and molecular characterization, mostly by Next Generation Sequencing (NGS). All potentially pathogenic variants have been confirmed through direct sequencing and familial segregation. Statistical evaluation of resulting data has been performed. RESULTS. In 28 probands we identified a pathogenic variant (p.Ser740*) in the RP1 gene that resulted significantly prevalent. Some patients, after careful interviewing, were found to share the same pedigree; we ultimately defined 20 family groups with no traceable consanguinity. CONCLUSIONS. The high prevalence of the p.Ser740* variant in RP patients from Western Sicily unveils the presence of a founder effect, which has implications for the molecular diagnosis of RCD in patients coming from this Italian region. This variant can be primarily searched in RP affected subjects displaying compatible mode of transmission and phenotype, with an advantage in terms of costs and analysis time. Moreover, given its high prevalence, RP1 p.Ser740* variant could represent a potential candidate for the development of therapeutic strategies based on gene editing or translational read-through therapy for suppression of nonsense variants.

Background: Studying patients carrying identical by descent (IBD) pathogenic gene variants allows to control for the disease-causing genetic background and to more accurately document the impact of modifiers. Familial hypercholesterolemia (FH) is characterized by elevated LDL-c levels, premature atherosclerosis and is often caused by defects in the LDLR gene. There is a high prevalence of FH in French Canada carry IBD FH-causing due to a founder effect from France in the 17th Century. Several FH patients currently living in French Canada (founder population) and in France (colonizing population) carry IBD FH-causing variants. The expression of FH is affected by environmental and genetic modifiers and patients with IBD variants may present different characteristics. Methods: In this study, we compared FH clinical expression patients carrying IBD LDLR pathogenic variants living in France or Canada. Four IBD variants, namely c.259T>G p.(Trp87Gly); c.2000G>A p.(Cys667Tyr); c.682G>A p.(Glu228Lys); and c.1048C>T p.(Arg350*) were selected. Untreated plasma lipid profiles, APOE genotype, cardiovascular risk factors and occurrence of symptomatic ASCVD were compared in 105 adult carriers (30 from France and 75 from French Canada). Results: All parameters were similar between the two populations, except for untreated total cholesterol (10.14 ± 1.89 mmol/L vs 8.65 ± 1.84 mmol/L, p=0.0006) and LDL-c concentrations (7.94 ± 1.86 mmol/L vs 6.93 ± 1.78 mmol/L, p=0.016) that were significantly higher in FH patients living in France, a trend that was observed in all studied LDLR variants. Conclusion: This study illustrates that FH patients sharing IBD pathogenic LDLR variants that have evolved in different geographic, cultural and socio-economic environments for hundreds of years, differ in term of cholesterol levels highlighting the importance of better understanding the interplay between genetic and environmental modulators of FH expression.

Introduction and objectives: arrhythmogenic cardiomyopathy (ACM) is a hereditary heart disease defined by the progressive replacement of the ventricular myocardium with fibroadipose tissue, which can act as a substrate for arrhythmias, sudden death, or even give rise to heart failure (HF). Sudden death is frequently the first manifestation of the disease, particularly among young patients. The aim of this study is to describe a new pathogenic variant in the PKP2 gene. Methods: A descriptive observational study that included 8 initially non-interrelated families with a diagnosis of ACM undergoing follow-up at our HF and Familial Cardiomyopathies Unit, who were carriers of the NM_004572.3:c.775_776insG; p. (Glu259Glyfs*77) variant in PKP2 gene. The genetic testing employed next-generation sequencing for the index cases, and the Sanger method for the targeted study with family members. We compiled personal and family histories, demographic and clinical characteristics, data from the additional tests at the time of diagnosis, and arrhythmic events at diagnosis and during follow-up. Results: We included 47 subjects, of whom 8 were index cases (17%). Among the evaluated family members, 16 (34%) were carriers of the genetic variant, 3 of whom also had a diagnosis of ACM. The majority were women (26 patients; 55.3%), with a mean age on diagnosis of 48.9 ± 18.6 years, and a median follow-up of 39 [24-59] months. Worthy of note are the high incidence of arrhythmic events as the form of presentation and in follow-up (21.5% and 20.9% respectively), and the onset of HF in 25% of the sample. The most frequent ventricular involvements were right (4 patients 16.7%) and biventricular (4 patients 16.7%); we found no statistical differences in any of the variables analysed. Conclusions: This variant is a pathogenic variant of gene PKP2 that has not previously been described and is not present in the control groups associated with ACM. It has incomplete penetrance, a highly variable phenotypic expressivity, and was identified in 8 families of our geographical area in Malaga (Andalusia, Spain), where we can establish a founder effect and describe the clinical and risk characteristics.

Cystic fibrosis (CF) diagnosis can be a challenge due to the large spectrum of pathogenic variants in the CFTR gene and the effects of complex alleles. Next-generation sequencing has improved our understanding of the contribution of these complex alleles to the wide spectrum of CF clinical symptoms and to the response to medications. Herein, we studied nine CF patients from six unrelated families carrying the complex allele p.[Ile148Thr;Ile1023_Val1024del] with a frequency of 0.18%. All the patients were from Central Mexico. This complex allele was found in trans with Class I and II pathogenic variants (PVs) such as [c.1521_1523del, p.(Phe508del), and c.3231_3232del, p.(Phe1078Profs*77)]. A targeted search of a dataset of 2,217 exomes from healthy individuals revealed that eight individuals (0.18%) carried the p.(Ile148Thr) variant, but only one (0.022%), who was also born in Central Mexico, was a carrier of the complex allele. These findings led us to hypothesize a founder effect for the p.[Ile148Thr;Ile1023_Val1024del] complex allele in Mexican patients with CF, probably through migration from the French-Canadian population in Mexico. Finally, protein modeling revealed that this complex allele disrupts the secondary structure of the CFTR protein and might alter the ion flow.

Fanconi anemia (FA) is a rare genetic disorder caused by pathogenic variants (PV) in at least 22 genes, which cooperate in the FA/BRCA pathway to maintain genome stability. PV in FANCA, FANCC, and FANCG account for most cases (~90%). This study evaluated the chromosomal, molecular, and phenotypic findings of a novel founder FANCG PV, identified in three patients with FA from the Mixe community of Oaxaca, Mexico. All patients presented chromosomal instability and a homozygous PV, FANCG: c.511-3_511-2delCA, identified by next-generation sequencing analysis. Bioinformatics predictions suggest that this deletion disrupts a splice acceptor site promoting the exon 5 skipping. Analysis of Cytoscan 750K arrays for haplotyping and global ancestry supported the Mexican origin and founder effect of the variant, reaffirming the high frequency of founder PV in FANCG. The degree of bone marrow failure and physical findings (described through the acronyms VACTERL-H and PHENOS) were used to depict the phenotype of the patients. Despite having a similar frequency of chromosomal aberrations and genetic constitution, the phenotype showed a wide spectrum of severity. The identification of a founder PV could help for a systematic and accurate genetic screening of patients with FA suspicion in this population.

Introduction: Previous research has suggested, that primary breast cancer (PBC) and ovarian cancer (OC) risks can be modified by mutation location in BRCA1 gene. In this study we assessed and compared the risks of contralateral breast cancer (CBC) and OC after the event of PBC in carriers of regionally frequent BRCA1 founder pathogenic variants (PV) c.5266dup and c.4035del. Subjects and Methods: In the analysis of CBC and OC risk, 1364 cases with BRCA1 PV and PBC were included. The control group consisted of 11350 consequent unselected and unscreened cases with PBC. The follow-up started at the time of PBC diagnosis and continued till the event of CBC or OC had occurred. The cumulative risks of CBC and OC were calculated using the Kaplan-Meier analysis. Risk factor for developing CBC/OC (age < 40 years) was calculated using cox proportional hazards model. Results: Cumulative 10 years risk of developing CBC was 3.0% in control group, and 20.1% in study group of BRCA1 carriers (log-rank p < 0.001). Cumulative risk of CBC at 10,15 and 20 years was 25.0%, 37.0% and 51.4% in PV c.5266dup subgroup, as opposed to 14.1%, 27.2% and 44.5% in PV c.4035del subgroup (log-rank p = 0.045). Age younger than 40 years at the time of PBC was risk factor for CBC (hazard ratio 2.06, 95% CI 1.83-2.29, p < 0.001). Cumulative risk of developing OC at 10 and 15 years was 1.0% and 1.2% in control group, 10.8% and 16.8% for PV c.5266dup, 13.5% and 30.8% for PV c.4035del. There was difference in OC risks between control group and BRCA1 carriers (log-rank p< 0.001). PV c.4035del showed higher risk of OC, compared to PV c.5266dup, however, this was of borderline statistical significance (log-rank p = 0.057). Age younger than 40 years at the time of PBC was not associated with any difference in future OC risks (hazard ratio 1.03, 95% CI 0.77-1.29, p = 0.23). Conclusion: The data of this study confirms previously established evidence that in cases of PBC the risk of future CBC and OC is increased significantly for BRCA1 carriers in comparison to general unscreened population. Moreover, BRCA1 PV c.5266dup is associated with higher CBC risk and possibly lower OC risk in comparison to BRCA1 PV c.4035del. Age younger than 40 years at diagnosis of PBC is risk factor for CBC, but does not seem to alter the risk of OC.