Impact of exposures to persistent endocrine disrupting compounds on the sperm methylome in regions associated with neurodevelopmental disorders

Background: Although autism spectrum disorder (ASD) is among the most heritable of neurodevelopmental disorders, the rapidly rising prevalence of ASD suggests that environmental factors may contribute to epigenetic modifications that can influence risk for ASD. Endocrine disrupting compounds (EDCs), such as the long-lived organochlorines, are of particular interest with respect to risk for autism because of their ability to interfere with sex hormones that have been implicated in ASD. Methods: Whole genome bisulfite sequencing was used to identify genome-wide differentially methylated regions (DMRs) in a total of 52 sperm samples from a cohort of Faroese men who were equally divided into high and low exposure groups based on their serum levels of the long-lived organochlorine 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE). Inhabitants of the Faroe Islands, who as a group are considered a genetic isolate, may be exposed to higher than average levels of such persistent EDCs because of their native diet that is enriched in pilot whale meat and blubber. Gene ontology and pathway analyses were used to determine enrichment in ASD-relevant pathways and functions among the DMR-associated genes. Results: DMRs were enriched in autism risk genes and could also discriminate between samples in high and low exposure groups. Functional and pathway analyses of these DMR-associated genes show significant enrichment for neurodevelopmental processes frequently impacted by ASD. Of note, the DMR-associated genes significantly overlap with those previously identified in sperm from fathers of children with ASD versus fathers of neurotypical children, thus suggesting a potential environmental mechanism for introducing ASD-associated epigenetic changes in the sperm methylome. Limitations: A limitation of this study is the relatively low number of samples, although this is somewhat offset by the use of a genetic isolate which reduces the genetic heterogeneity that is often a major challenge in epigenetic studies. Another limitation is the lack of a completely unexposed set of samples for comparisons since persistent EDCs can be detected in a majority of individuals. Conclusion: Results of this study show that elevated exposure to certain organochlorines is associated with genome-wide DNA methylation patterns in sperm affecting genes involved in neurological functions and developmental disorders, including ASD.

Analysis of Italian BRCA1/2 Pathogenic Variants Identifies a Private Spectrum in the Population from the Bergamo Province in Northern Italy

Germline pathogenic variants (PVs) in the BRCA1 or BRCA2 genes cause high breast cancer risk. Recurrent or founder PVs have been described worldwide including some in the Bergamo province in Northern Italy. The aim of this study was to compare the BRCA1/2 PV spectra of the Bergamo and of the general Italian populations. We retrospectively identified at five Italian centers 1019 BRCA1/2 PVs carrier individuals affected with breast cancer and representative of the heterogeneous national population. Each individual was assigned to the Bergamo or non-Bergamo cohort based on self-reported birthplace. Our data indicate that the Bergamo BRCA1/2 PV spectrum shows less heterogeneity with fewer different variants and an average higher frequency compared to that of the rest of Italy. Consistently, four PVs explained about 60% of all carriers. The majority of the Bergamo PVs originated locally with only two PVs clearly imported. The Bergamo BRCA1/2 PV spectrum appears to be private. Hence, the Bergamo population would be ideal to study the disease risk associated with local PVs in breast cancer and other disease-causing genes. Finally, our data suggest that the Bergamo population is a genetic isolate and further analyses are warranted to prove this notion.

Effect of inbreeding on type 2 diabetes-related metabolites in a Dutch genetic isolate

Autozygosity, meaning inheritance of an ancestral allele in the homozygous state is known to lead bi-allelic mutations that manifest their effects through the autosomal recessive inheritance pattern. Autosomal recessive mutations are known to be the underlying cause of several Mendelian metabolic diseases, especially among the offspring of related individuals. In line with this, inbreeding coefficient of an individual as a measure of cryptic autozygosity among the general population is known to lead adverse metabolic outcomes including type 2 diabetes (T2DM), a multifactorial metabolic disease for which the recessive genetic causes remain unknown. In order to unravel such effects for multiple metabolic facades of the disease, we investigated the relationship between the excess of homozygosity and the metabolic signature of T2DM. We included a set of heritable 143 circulating markers associated with fasting glucose in a Dutch genetic isolate Erasmus Rucphen Family (ERF) of up to 2,580 individuals. We calculated individual whole genome-based, exome-based and pedigree-based inbreeding coefficients and tested their influence on the T2DM-related metabolites as well as T2DM risk factors. We also performed model supervised genome-wide association analysis (GWAS) for the metabolites which significantly correlate with inbreeding values. Inbreeding value of the population significantly and positively correlated with associated with risk factors of T2DM: body-mass index (BMI), glucose, insulin resistance, fasting insulin and waist-hip ratio. We found that inbreeding influenced 32.9% of the T2DM-related metabolites, clustering among chemical groups of lipoproteins, amino-acids and phosphatidylcholines, whereas 80 % of these significant associations were independent of the BMI. The most remarkable effect of inbreeding is observed for S-HDL-ApoA1, for which we show evidence of the novel DISP1 genetic region discovered by model supervised GWAS, in the ERF population. In conclusion, we show that inbreeding effects human metabolism and genetic models other than the globally used additive model is worth considering for study of metabolic phenotypes.