Exploring digenic inheritance in arrhythmogenic cardiomyopathy.

BACKGROUND: Arrhythmogenic cardiomyopathy (ACM) is an inherited genetic disorder, characterized by the substitution of heart muscle with fibro-fatty tissue and severe ventricular arrhythmias, often leading to heart failure and sudden cardiac death. ACM is considered a monogenic disorder, but the low penetrance of mutations identified in patients suggests the involvement of additional genetic or environmental factors. METHODS: We used whole exome sequencing to investigate digenic inheritance in two ACM families where previous diagnostic tests have revealed a PKP2 mutation in all affected and some healthy individuals. In family members with PKP2 mutations we determined all genes that harbor variants in affected but not in healthy carriers or vice versa. We computationally prioritized the most likely candidates, focusing on known ACM genes and genes related to PKP2 through protein interactions, functional relationships, or shared biological processes. RESULTS: We identified four candidate genes in family 1, namely DAG1, DAB2IP, CTBP2 and TCF25, and eleven candidate genes in family 2. The most promising gene in the second family is TTN, a gene previously associated with ACM, in which the affected individual harbors two rare deleterious-predicted missense variants, one of which is located in the protein's only serine kinase domain. CONCLUSIONS: In this study we report genes that might act as digenic players in ACM pathogenesis, on the basis of co-segregation with PKP2 mutations. Validation in larger cohorts is still required to prove the utility of this model.

2q37 as a susceptibility locus for idiopathic basal ganglia calcification (IBGC) in a large South Tyrolean family.

Familial idiopathic basal ganglia calcification (FIBGC) is an inherited neurodegenerative disorder characterized by the accumulation of calcium deposits in different brain regions, particularly in the basal ganglia. FIBGC usually follows an autosomal dominant pattern of inheritance. Despite the mapping to chromosome 14q of a susceptibility locus for IBGC (IBCG1) in one family, this locus has been excluded in several others, demonstrating genetic heterogeneity in this disorder. The etiology of this disorder thus remains largely unknown. Using a large extended multigenerational Italian family from South Tyrol with 17 affected in a total of 56 members, we performed a genome-wide linkage analysis in which we were able to exclude linkage to the IBCG1 locus on chromosome 14q and obtain evidence of a novel locus on chromosome 2q37. Electronic supplementary material. The online version of this article (doi:10.1007/s12031-009-9287-3) contains supplementary material, which is available to authorized users.

ParkScreen: a low-cost rapid linkage marker panel for Parkinson's disease.

A genetic marker screening panel, ParkScreen, optimized for simultaneous marker amplification, was constructed to test or exclude linkage in families with parkinsonism or Parkinson's disease, using only a few affected individuals per family. ParkScreen functionality was proven by detection of linkage to PARK2 in a family with known Parkin mutations, exclusion of linkage to several of the known loci, and detection of suggestive linkage to PARK8, PARK3, and PARK11 in some families. In a novel approach, we also tested the ability of ParkScreen to screen patients originating from isolated populations. Using apparently sporadic patients from geographically isolated Alpine villages, suggestive linkage to PARK11 was found in one village. ParkScreen is a useful and inexpensive tool that allows the rapid screening of patients in families suitable for clinical follow-up and further characterization in order to identify specific mutations or novel genes.

Enhanced sensitivity of the RET proto-oncogene to ionizing radiation in vitro.

Exposure to ionizing radiation is a well-known risk factor for a number of human cancers, including leukemia and thyroid cancer. It has been known for a long time that exposure of cells to radiation results in extensive DNA damage; however, a small number of studies have tried to explain the mechanisms of radiation-induced carcinogenesis. The high prevalence of RET/PTC rearrangements in patients who have received external radiation, and the evidence of in vitro induction of RET rearrangements in human cells, suggest an enhanced sensitivity of the RET genomic region to damage by ionizing radiation. To assess whether RET is indeed more sensitive to radiations than other genomic regions, we used a COMET assay coupled with fluorescence in situ hybridization, which allows the measurement of DNA fragmentation in defined genomic regions of single cells. We compared the initial DNA damage of the genomic regions of RET, CXCL12/SDF1, ABL, MYC, PLA2G2A, p53, and JAK2 induced by ionizing radiation in both a lymphoblastoid and a fetal thyroid cell line. In both cell lines, RET fragmentation was significantly higher than in other genomic regions. Moreover, a differential distribution of signals within the COMET was associated with a higher percentage of RET fragments in the tail. RET was more susceptible to fragmentation in the thyroid-derived cells than in lymphoblasts. This enhanced susceptibility of RET to ionizing radiation suggests the possibility of using it as a radiation exposure marker.

Exclusion of linkage to chromosome 14q in a large South Tyrolean family with Idiopathic Basal Ganglia Calcification (IBGC).

Familial Idiopathic Basal Ganglia Calcification (FIBGC) is a neurodegenerative syndrome that usually follows an autosomal dominant pattern of inheritance. Linkage to only one locus on chromosome 14q (IBCG1) has been described so far. We identified and characterized a large multigenerational Italian family from a population isolate with 14 FIBGC affected members. Linkage analysis excluded the IBCG1 locus, thus demonstrating further locus heterogeneity for this disease.

Linkage analysis identifies a novel locus for restless legs syndrome on chromosome 2q in a South Tyrolean population isolate.

Restless legs syndrome (RLS) is a common neurological condition with three loci (12q, 14q, and 9p) described so far, although none of these genes has yet been identified. We report a genomewide linkage scan of patients with RLS (n=37) assessed in a population isolate (n=530) of South Tyrol (Italy). Using both nonparametric and parametric analyses, we initially obtained suggestive evidence of a novel locus on chromosome 2q, with nominal evidence of linkage on chromosomes 5p and 17p. Follow-up genotyping yielded significant evidence of linkage (nonparametric LOD score 5.5, P

Restless legs syndrome: epidemiological and clinicogenetic study in a South Tyrolean population isolate.

Genetic contributions to restless legs syndrome (RLS) have been consistently recognized from population and family studies. To determine the clinical and genetic features of RLS in a population isolate and explore linkage to three previously described susceptibility loci on chromosomes 12q, 14q, and 9p, respectively, an isolated population in the South Tyrolean Alps was identified and 530 adults participated in the study. Using a two-step strategy, 47 patients with idiopathic RLS were ascertained. The prevalence in the population was 8.9%. Twenty-eight patients (59.6%) had at least one affected first-degree relative and were classified as hereditary cases. In a single extended pedigree, linkage to known RLS loci was investigated specifying autosomal dominant and recessive models; parametric and nonparametric multipoint linkage scores were computed. None of the calculated linkage scores was suggestive of linkage between RLS and any of the three investigated loci. This study was conducted in a population isolate providing for a homogeneous genetic and environmental background. The absence of a suggestive linkage signal at the three known RLS susceptibility loci is indicative of further locus heterogeneity of this frequent disorder and encourages further studies to unveil the genetic causes of RLS.

Genetic structure in contemporary south Tyrolean isolated populations revealed by analysis of Y-chromosome, mtDNA, and Alu polymorphisms.

Most of the inhabitants of South Tyrol in the eastern Italian Alps can be considered isolated populations because of their physical separation by mountain barriers and their sociocultural heritage. We analyzed the genetic structure of South Tyrolean populations using three types of genetic markers: Y-chromosome, mitochondrial DNA (mtDNA), and autosomal Alu markers. Using random samples taken from the populations of Val Venosta, Val Pusteria, Val Isarco, Val Badia, and Val Gardena, we calculated genetic diversity within and among the populations. Microsatellite diversity and unique event polymorphism diversity (on the Y chromosome) were substantially lower in the Ladin-speaking population of Val Badia compared to the neighboring German-speaking populations. In contrast, the genetic diversity of mtDNA haplotypes was lowest for the upper Val Venosta and Val Pusteria. These data suggest a low effective population size, or little admixture, for the gene pool of the Ladin-speaking population from Val Badia. Interestingly, this is more pronounced for Ladin males than for Ladin females. For the pattern of genetic Alu variation, both Ladin samples (Val Gardena and Val Badia) are among the samples with the lowest diversity. An admixture analysis of one German-speaking valley (Val Venosta) indicates a relatively high genetic contribution of Ladin origin. The reduced genetic diversity and a high genetic differentiation in the Rhaetoroman- and German-speaking South Tyrolean populations may constitute an important basis for future medical genetic research and gene mapping studies in South Tyrol.