Fabry disease (FD) is an X-linked hereditary defect of glycosphingolipid storage caused by mutations in the gene encoding the lysosomal hydrolase α-galactosidase A (GLA, α-gal A). To date, over 400 mutations causing amino acid substitutions have been described. Most of these mutations are related to the classical Fabry phenotype. Generally in lysosomal storage disorders a reliable genotype/phenotype correlation is difficult to achieve, especially in FD with its X-linked mode of inheritance. In order to predict the metabolic consequence of a given mutation, we combined in vitro enzyme activity with in vivo biomarker data. Furthermore, we used the pharmacological chaperone (PC) 1-deoxygalactonojirimycin (DGJ) as a tool to analyse the influence of individual mutations on subcellular organelle-trafficking and stability. We analysed a significant number of mutations and correlated the obtained properties to the clinical manifestation related to the mutation in order to improve our knowledge of the identity of functional relevant amino acids. Additionally, we illustrate the consequences of different mutations on plasma lyso-globotriaosylsphingosine (lyso-Gb3) accumulation in the patients' plasma, a biomarker proven to reflect the impaired substrate clearance caused by specific mutations. The established system enables us to provide information for the clinical relevance of PC therapy for a given mutant. Finally, in order to generate reliable predictions of mutant GLA defects we compared the different data sets to reveal the most coherent system to reflect the clinical situation.

ContextIn contrast to the large number of studies in children, there is little information on the contribution of genetic factors to Attention Deficit Hyperactivity Disorder (ADHD) in adults.ObjectiveTo estimate the heritability of ADHD in adults as assessed by the ADHD index scored from the CAARS (Conners' Adult ADHD Rating Scales).DesignPhenotype data from over 12,000 adults (twins, siblings and parents) registered with the Netherlands Twin Register were analyzed using genetic structural equation modeling.Main outcome measuresHeritability estimates for ADHD from the twin-family study.ResultsHeritability of ADHD in adults is estimated around 30% in men and women. There is some evidence for assortative mating. All familial transmission is explained by genetic inheritance, there is no support for the hypothesis that cultural transmission from parents to offspring is important.ConclusionHeritability for ADHD features in adults is present, but is substantially lower than it is in children.

The synapsin 2 (Syn2) gene (3p25) is implicated in synaptogenesis, neurotransmitter release, and the localization of nitric oxide synthase to the proximity of its targets. In this study we investigated linkage and association between the Syn2 locus and schizophrenia. 37 pedigrees of Northern European ancestry from the NIMH Human Genetics Initiative collection were used. Four microsatellites and twenty SNPs were genotyped. Linkage (FASTLINK) and association (TRANSMIT, PDTPHASE) between markers and schizophrenia were evaluated. A maximum heterogeneity LOD of 1.93 was observed at marker D3S3434 with a recessive mode of inheritance. Significant results were obtained for association with schizophrenia using TRANSMIT (minimum nominal p=0.0000005) and PDTPHASE (minimum nominal p=0.014) using single marker analyses. Haplotype analysis using markers in introns 5 and 6 of Syn2 provided a single haplotype that is significantly associated with schizophrenia using TRANSMIT (nominal p<0.00000001) and PDTPHASE (nominal p=0.02). Simulation studies confirm the global significance of these results, but demonstrate that the small p-values generated by the bootstrap routine of TRANSMIT can be consistently anticonservative. Review of the literature suggests that Syn2 is likely to be involved in the etiology or pathogenesis of schizophrenia.

C auses of individual differences in happiness, as assessed with the Subjective Happiness Scale, are investigated in a large of sample twins and siblings from the Netherlands Twin Register. Over 12,000 twins and siblings, average age 24.7 years (range 12 to 88), took part in the study. A genetic model with an age by sex design was fitted to the data with structural equation modeling in Mx. The heritability of happiness was estimated at 22% for males and 41% in females. No effect of age was observed. To identify the genomic regions contributing to this heritability, a genome-wide linkage study for happiness was conducted in sibling pairs. A subsample of 1157 offspring from 441 families was genotyped with an average of 371 micro-satellite markers per individual. Phenotype and genotype data were analyzed in MERLIN with multipoint variance component linkage analysis and age and sex as covariates. A linkage signal (logarithm of odds score 2.73, empirical p value 0.095) was obtained at the end of the long arm of chromosome 19 for marker D19S254 at 110 cM. A second suggestive linkage peak was found at the short arm of chromosome 1 (LOD of 2.37) at 153 cM, marker D1S534 (empirical p value of .209). These two regions of interest are not overlapping with the regions found for contrasting phenotypes (such as depression, which is negatively associated with happiness). Further linkage and future association studies are warranted.

Genetic testing for hereditary breast and/or ovarian cancer mostly relies on laborious molecular tools that use Sanger sequencing to scan for mutations in the BRCA1 and BRCA2 genes. We explored a more efficient genetic screening strategy based on next-generation sequencing of the BRCA1 and BRCA2 genes in 210 hereditary breast and/or ovarian cancer patients. We first validated this approach in a cohort of 115 samples with previously known BRCA1 and BRCA2 mutations and polymorphisms. Genomic DNA was amplified using the Ion AmpliSeq BRCA1 and BRCA2 panel. The DNA Libraries were pooled, barcoded, and sequenced using an Ion Torrent Personal Genome Machine sequencer. The combination of different robust bioinformatics tools allowed detection of all previously known pathogenic mutations and polymorphisms in the 115 samples, without detecting spurious pathogenic calls. We then used the same assay in a discovery cohort of 95 uncharacterized hereditary breast and/or ovarian cancer patients for BRCA1 and BRCA2. In addition, we describe the allelic frequencies across 210 hereditary breast and/or ovarian cancer patients of 74 unique definitely and likely pathogenic and uncertain BRCA1 and BRCA2 variants, some of which have not been previously annotated in the public databases. Targeted next-generation sequencing is ready to substitute classic molecular methods to perform genetic testing on the BRCA1 and BRCA2 genes and provides a greater opportunity for more comprehensive testing of at-risk patients.

Molecular characterization is important for an accurate diagnosis in hereditary spastic paraplegia (HSP). Mutations in the gene SPAST (SPG4) are the most common cause of autosomal dominant forms. We performed targeted next generation sequencing (NGS) in a SPAST-negative HSP sample. Forty-four consecutive HSP patients were recruited from an adult neurogenetics clinic in Sydney, Australia. SPAST mutations were confirmed in 17 subjects, and therefore 27 SPAST-negative patients were entered into this study. Patients were screened according to mode of inheritance using a PCR-based library and NGS (Roche Junior 454 sequencing platform). The screening panel included ten autosomal dominant (AD) and nine autosomal recessive (AR) HSP-causing genes. A genetic cause for HSP was identified in 25.9 % (7/27) of patients, including 1/12 classified as AD and 6/15 as AR or sporadic inheritance. Several forms of HSP were identified, including one patient with SPG31, four with SPG7 (with one novel SPG7 mutation) and two with SPG5 (including two novel CYP7B1 frameshift mutations). Additional clinical features were noted, including optic atrophy and ataxia for patients with SPG5 and ataxia and a chronic progressive external ophthalmoplegia-like phenotype for SPG7. This protocol enabled the identification of a genetic cause in approximately 25 % of patients in whom one of the most common genetic forms of HSP (SPG4) was excluded. Targeted NGS may be a useful method to screen for mutations in multiple genes associated with HSP. More studies are warranted to determine the optimal approach to achieve a genetic diagnosis in this condition.

Attention deficit/hyperactivity disorder (ADHD) is a neurodevelopmental phenotype that persists into adulthood. This study investigated the heritability of inattentive and hyperactive symptoms and of total ADHD symptomatology load (ADHD index) in adults and performed linkage scans for these dimensions. Data on sibling pairs and their family members from the Netherlands Twin Register with genotype and phenotype data for inattention, hyperactivity and ADHD index (∼750 sib-pairs) were analyzed. Phenotypes were assessed with the short self-report form of the Conners' Adult ADHD Rating Scales (CAARS). Heritabilities were estimated in SOLAR under polygenic models. Genome-wide linkage scans were performed using variance components (VC) in MERLIN and MINX and model-based linkage analysis was carried out in MENDEL with empirical evaluation of the results via simulations. Heritability estimates for inattention, hyperactivity and ADHD index were 35%, 23%, and 31%, respectively. Chromosomes 18q21.31-18q21.32 (VC LOD = 4.58, p(emp)  = 0.0026) and 2p25.1 (LOD = 3.58, p(emp)  = 0.0372) provided significant evidence for linkage for inattention and the ADHD index, respectively. The QTL on chromosome 2p25.1 also showed suggestive linkage for hyperactivity. Two additional suggestive QTLs for hyperactivity and the ADHD index shared the same location on chromosome 3p24.3-3p24.1. Finally, a suggestive QTL on 8p23.3-8p23.2 for hyperactivity was also found. Heritability of inattention, hyperactivity and total ADHD symptoms is lower in adults than in children. Chromosomes 18q and 2p are likely to harbor genes that influence several aspects of adult ADHD.

We recently mapped a quantitative trait locus for monocyte counts to chromosome 9q31 (rs7023923). Here we extend this work by showing with two independent approaches that rs7023923 regulates the expression levels of the nearby LPAR1 gene (P<0.0001), specifically implicating this gene in monocyte development. Furthermore, we tested 10 additional loci identified in the original analysis for replication in 1,122 individuals and confirm that rs6740847 near the alpha-4-integrin gene (ITGA4) associates with variation in monocyte counts (combined P=2.7×10(-10)). This variant is in complete linkage disequilibrium (r(2) =1) with a previously reported eQTL for ITGA4 (rs2124440), indicating that this is the likely causal gene in the region. Our results indicate that rs7023923 and rs6740847 respectively upregulate LPAR1 and downregulate ITGA4 expression and this increases the number of monocytes circulating in the peripheral blood. Further studies that investigate the downstream mechanism involved and the impact on immune function are warranted.