Author Correction: Susceptible genes and disease mechanisms identified in frontotemporal dementia and frontotemporal dementia with Amyotrophic Lateral Sclerosis by DNA-methylation and GWAS

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Susceptible genes and disease mechanisms identified in frontotemporal dementia and frontotemporal dementia with Amyotrophic Lateral Sclerosis by DNA-methylation and GWAS

Frontotemporal dementia (FTD) is a neurodegenerative disorder predominantly affecting the frontal and temporal lobes. Genome-wide association studies (GWAS) on FTD identified only a few risk loci. One of the possible explanations is that FTD is clinically, pathologically, and genetically heterogeneous. An important open question is to what extent epigenetic factors contribute to FTD and whether these factors vary between FTD clinical subgroup. We compared the DNA-methylation levels of FTD cases (n = 128), and of FTD cases with Amyotrophic Lateral Sclerosis (FTD-ALS; n = 7) to those of unaffected controls (n = 193), which resulted in 14 and 224 candidate genes, respectively. Cluster analysis revealed significant class separation of FTD-ALS from controls. We could further specify genes with increased susceptibility for abnormal gene-transcript behavior by jointly analyzing DNA-methylation levels with the presence of mutations in a GWAS FTD-cohort. For FTD-ALS, this resulted in 9 potential candidate genes, whereas for FTD we detected 1 candidate gene (ELP2). Independent validation-sets confirmed the genes DLG1, METTL7A, KIAA1147, IGHMBP2, PCNX, UBTD2, WDR35, and ELP2/SLC39A6 among others. We could furthermore demonstrate that genes harboring mutations and/or displaying differential DNA-methylation, are involved in common pathways, and may therefore be critical for neurodegeneration in both FTD and FTD-ALS.

Genetic factors explain half of all variance in serum eosinophil cationic protein

BACKGROUND

Eosinophil cationic protein (ECP) is one of four basic proteins of the secretory granules of eosinophils. It has a variety of functions associated with inflammatory responses. Little is known about the causes for variation in serum ECP levels.

AIM

To identify factors associated with variation in serum ECP and to determine the relative proportion of the variation in ECP due to genetic and non-genetic factors, in an adult twin sample.

METHODS

A sample of 575 twins, selected through a proband with self-reported asthma, had serum ECP, lung function, airway responsiveness to methacholine, exhaled nitric oxide, and skin test reactivity, measured. Linear regression analysis and variance component models were used to study factors associated with variation in ECP and the relative genetic influence on ECP levels.

RESULTS

Sex (regression coefficient = -0.107, P < 0.001), body mass index (BMI) (0.007, P = 0.028), and airway responsiveness to methacholine (0.074, P = 0.001) were significantly associated with ECP. Adjusted for these factors, ECP correlated 0.53 (P < 0.001) and 0.27 (P = 0.001) in monozygotic and dizygotic twins, respectively (P-value for difference = 0.05). According to the most parsimonious variance component model, genetic factors accounted for 57% (CI: 42-72%, P < 0.001) of the variance in ECP levels, whereas the remainder (43%) was ascribable to non-shared environmental factors. The genetic correlation between ECP and airway responsiveness to methacholine was statistically non-significant (r = -0.11, P = 0.50).

CONCLUSION

Around half of all variance in serum ECP is explained by genetic factors. Serum ECP is influenced by sex, BMI, and airway responsiveness. Serum ECP and airway responsiveness seem not to share genetic variance.

Functional characterization of the PCLO p.Ser4814Ala variant associated with major depressive disorder reveals cellular but not behavioral differences

Genome-wide association studies have suggested a role for a genetic variation in the presynaptic gene PCLO in major depressive disorder (MDD). As with many complex traits, the PCLO variant has a small contribution to the overall heritability and the association does not always replicate. One variant (rs2522833, p.Ser4814Ala) is of particular interest given that it is a common, nonsynonymous exon variant near a calcium-sensing part of PCLO. It has been suggested that the molecular effects of such variations penetrate to a variable extent in the population due to phenotypic and genotypic heterogeneity at the population level. More robust effects may be exposed by studying such variations in isolation, in a more homogeneous context. We tested this idea by modeling PCLO variation in a mouse knock-in model expressing the Pclo(SA)(/)(SA) variant. In the highly homogeneous background of inbred mice, two functional effects of the SA-variation were observed at the cellular level: increased synaptic Piccolo levels, and 30% increased excitatory synaptic transmission in cultured neurons. Other aspects of Piccolo function were unaltered: calcium-dependent phospholipid binding, synapse formation in vitro, and synaptic accumulation of synaptic vesicles. Moreover, anxiety, cognition and depressive-like behavior were normal in Pclo(SA)(/)(SA) mice. We conclude that the PCLO p.Ser4814Ala missense variant produces mild cellular phenotypes, which do not translate into behavioral phenotypes. We propose a model explaining how (subtle) cellular phenotypes do not penetrate to the mouse behavioral level but, due to genetic and phenotypic heterogeneity and non-linearity, can produce association signals in human population studies.

Attentional switching forms a genetic link between attention problems and autistic traits in adults

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) symptoms and autistic traits often occur together. The pattern and etiology of co-occurrence are largely unknown, particularly in adults. This study investigated the co-occurrence between both traits in detail, and subsequently examined the etiology of the co-occurrence, using two independent adult population samples. Method Data on ADHD traits (Inattention and Hyperactivity/Impulsivity) were collected in a population sample (S1, n = 559) of unrelated individuals. Data on Attention Problems (AP) were collected in a population-based family sample of twins and siblings (S2, n = 560). In both samples five dimensions of autistic traits were assessed (social skills, routine, attentional switching, imagination, patterns).

RESULTS

Hyperactive traits (S1) did not correlate substantially with the autistic trait dimensions. For Inattention (S1) and AP (S2), the correlations with the autistic trait dimensions were low, apart from a prominent correlation with the attentional switching scale (0.47 and 0.32 respectively). Analyses in the genetically informative S2 revealed that this association could be explained by a shared genetic factor.

CONCLUSIONS

Our findings suggest that the co-occurrence of ADHD traits and autistic traits in adults is not determined by problems with hyperactivity, social skills, imagination or routine preferences. Instead, the association between those traits is due primarily to shared attention-related problems (inattention and attentional switching capacity). As the etiology of this association is purely genetic, biological pathways involving attentional control could be a promising focus of future studies aimed at unraveling the genetic causes of these disorders.

High-throughput phenotyping of avoidance learning in mice discriminates different genotypes and identifies a novel gene

Recognizing and avoiding aversive situations are central aspects of mammalian cognition. These abilities are essential for health and survival and are expected to have a prominent genetic basis. We modeled these abilities in eight common mouse inbred strains covering ∼75% of the species' natural variation and in gene-trap mice (>2000 mice), using an unsupervised, automated assay with an instrumented home cage (PhenoTyper) containing a shelter with two entrances. Mice visited this shelter for 20-1200 times/24 h and 71% of all mice developed a significant and often strong preference for one entrance. Subsequently, a mild aversive stimulus (shelter illumination) was automatically delivered when mice used their preferred entrance. Different genotypes developed different coping strategies. Firstly, the number of entries via the preferred entrance decreased in DBA/2J, C57BL/6J and 129S1/SvImJ, indicating that these genotypes associated one specific entrance with the aversive stimulus. Secondly, mice started sleeping outside (C57BL/6J, DBA/2J), indicating they associated the shelter, in general, with the aversive stimulus. Some mice showed no evidence for an association between the entrance and the aversive light, but did show markedly shorter shelter residence times in response to illumination, indicating they did perceive illumination as aversive. Finally, using this assay, we screened 43 different mutants, which yielded a novel gene, specc1/cytospinB. This mutant showed profound and specific delay in avoidance learning. Together, these data suggest that different genotypes express distinct learning and/or memory of associations between shelter entrance and aversive stimuli, and that specc1/cytospinB is involved in this aspect of cognition.

Heritability of reproductive hormones in adult male twins

BACKGROUND

Proper functioning of the male reproductive axis depends on complex feedback systems between several hormones. In this study, the genetic contribution of various endocrine components of the hypothalamic-pituitary-testicular axis is evaluated and previously observed differences in FSH and inhibin B levels between mono- (MZ) and dizygotic (DZ) twins are re-investigated.

METHODS

Inhibin B, FSH, LH, sex hormone-binding globulin (SHBG) and testosterone levels were assayed in 128 adult males (20 MZ twin pairs, 7 single MZ twins, 10 DZ twin pairs, 27 single DZ twins and 34 siblings of twins, constituting 10 sibling pairs), aged 15.6-68.7 years. Hormone levels were compared across zygosity groups and heritability estimates were obtained using maximum likelihood variance component analysis.

RESULTS

Heritability estimates ranged from 56% (testosterone) to 81% (inhibin B and SHBG). For LH and FSH, the heritability was estimated at 68% and 80% respectively. No mean differences in hormone levels were observed across groups.

CONCLUSIONS

All measured hormones are highly heritable. A difference in the FSH-inhibin B feedback system between DZ twin males and MZ twin males could not be confirmed.