T. Conrad Gilliam

Mutations in LGI1 cause autosomal-dominant partial epilepsy with auditory features

The epilepsies are a common, clinically heterogeneous group of disorders defined by recurrent unprovoked seizures. Here we describe identification of the causative gene in autosomal-dominant partial epilepsy with auditory features (ADPEAF, MIM 600512), a rare form of idiopathic lateral temporal lobe epilepsy characterized by partial seizures with auditory disturbances. We constructed a complete, 4.2-Mb physical map across the genetically implicated disease-gene region, identified 28 putative genes (Fig. 1) and resequenced all or part of 21 genes before identifying presumptive mutations in one copy of the leucine-rich, glioma-inactivated 1 gene (LGI1) in each of five families with ADPEAF. Previous studies have indicated that loss of both copies of LGI1 promotes glial tumor progression. We show that the expression pattern of mouse Lgi1 is predominantly neuronal and is consistent with the anatomic regions involved in temporal lobe epilepsy. Discovery of LGI1 as a cause of ADPEAF suggests new avenues for research on pathogenic mechanisms of idiopathic epilepsies.

Desmoglein 4 in Hair Follicle Differentiation and Epidermal Adhesion: Evidence from Inherited Hypotrichosis and Acquired Pemphigus Vulgaris

Cell adhesion and communication are interdependent aspects of cell behavior that are critical for morphogenesis and tissue architecture. In the skin, epidermal adhesion is mediated in part by specialized cell-cell junctions known as desmosomes, which are characterized by the presence of desmosomal cadherins, known as desmogleins and desmocollins. We identified a cadherin family member, desmoglein 4, which is expressed in the suprabasal epidermis and hair follicle. The essential role of desmoglein 4 in skin was established by identifying mutations in families with inherited hypotrichosis, as well as in the lanceolate hair mouse. We also show that DSG4 is an autoantigen in pemphigus vulgaris. Characterization of the phenotype of naturally occurring mutant mice revealed disruption of desmosomal adhesion and perturbations in keratinocyte behavior. We provide evidence that desmoglein 4 is a key mediator of keratinocyte cell adhesion in the hair follicle, where it coordinates the transition from proliferation to differentiation.

The neuronal ceroid lipofuscinoses in human EPMR and mnd mutant mice are associated with mutations in CLN8

The neuronal ceroid lipofuscinoses (NCLs) are a genetically heterogeneous group of progressive neurodegenerative disorders characterized by the accumulation of autofluorescent lipopigment in various tissues. Progressive epilepsy with mental retardation (EPMR, MIM 600143) was recently recognized as a new NCL subtype (CLN8). It is an autosomal recessive disorder characterized by onset of generalized seizures between 5 and 10 years, and subsequent progressive mental retardation. Here we report the positional cloning of a novel gene, CLN8, which is mutated in EPMR. It encodes a putative transmembrane protein. EPMR patients were homozygous for a missense mutation (70C→G, R24G) that was not found in homozygosity in 433 controls. We also cloned the mouse Cln8 sequence. It displays 82% nucleotide identity with CLN8, conservation of the codon harbouring the human mutation and is localized to the same region as the motor neuron degeneration mouse, mnd, a naturally occurring mouse NCL (ref. 4). In mnd/mnd mice, we identified a homozygous 1-bp insertion (267-268insC, codon 90) predicting a frameshift and a truncated protein. Our data demonstrate that mutations in these orthologous genes underlie NCL phenotypes in human and mouse, and represent the first description of the molecular basis of a naturally occurring animal model for NCL.

Novel Submicroscopic Chromosomal Abnormalities Detected in Autism Spectrum Disorder

BACKGROUND One genetic mechanism known to be associated with autism spectrum disorders (ASD) is chromosomal abnormalities. The identification of copy number variants (CNV), i.e., microdeletions and microduplications that are undetectable at the level of traditional cytogenetic analysis, allows the potential association of submicroscopic chromosomal imbalances and human disease. METHODS We performed array comparative genomic hybridization (aCGH) utilizing a 19K whole genome tiling path bacterial artificial chromosome (BAC) microarray on 397 unrelated subjects with autism spectrum disorder. Common CNV were excluded using a control group comprised of 372 individuals from the National Institute of Mental Health (NIMH) Genetics Initiative Control samples. Confirmation studies were performed on all remaining CNV using fluorescence in situ hybridization (FISH), microsatellite analysis, and/or quantitative polymerase chain reaction (PCR) analysis. RESULTS A total of 51 CNV were confirmed in 46 ASD subjects. Three maternal interstitial duplications of 15q11-q13 known to be associated with ASD were identified. The other 48 CNV ranged in size from 189 kilobase (kb) to 5.5 megabase (Mb) and contained from 0 to approximately 40 National Center for Biotechnology Information (NCBI) Reference Sequence (RefSeq) genes. Seven CNV were de novo and 44 were inherited. CONCLUSIONS Fifty-one autism-specific CNV were identified in 46 of 397 ASD patients using a 19K BAC microarray for an overall rate of 11.6%. These microdeletions and microduplications cause gene dosage imbalance in 272 genes, many of which could be considered as candidate genes for autism.

A Genomewide Screen of 345 Families for Autism-Susceptibility Loci

We previously reported a genomewide scan to identify autism-susceptibility loci in 110 multiplex families, showing suggestive evidence (P <.01) for linkage to autism-spectrum disorders (ASD) on chromosomes 5, 8, 16, 19, and X and showing nominal evidence (P <.05) on several additional chromosomes (2, 3, 4, 10, 11, 12, 15, 18, and 20). In this follow-up analysis we have increased the sample size threefold, while holding the study design constant, so that we now report 345 multiplex families, each with at least two siblings affected with autism or ASD phenotype. Along with 235 new multiplex families, 73 new microsatellite markers were also added in 10 regions, thereby increasing the marker density at these strategic locations from 10 cM to approximately 2 cM and bringing the total number of markers to 408 over the entire genome. Multipoint maximum LOD scores (MLS) obtained from affected-sib-pair analysis of all 345 families yielded suggestive evidence for linkage on chromosomes 17, 5, 11, 4, and 8 (listed in order by MLS) (P <.01). The most significant findings were an MLS of 2.83 (P =.00029) on chromosome 17q, near the serotonin transporter (5-hydroxytryptamine transporter [5-HTT]), and an MLS of 2.54 (P =.00059) on 5p. The present follow-up genome scan, which used a consistent research design across studies and examined the largest ASD sample collection reported to date, gave either equivalent or marginally increased evidence for linkage at several chromosomal regions implicated in our previous scan but eliminated evidence for linkage at other regions.

Combined Analysis from Eleven Linkage Studies of Bipolar Disorder Provides Strong Evidence of Susceptibility Loci on Chromosomes 6q and 8q

Several independent studies and meta-analyses aimed at identifying genomic regions linked to bipolar disorder (BP) have failed to find clear and consistent evidence of linkage regions. Our hypothesis is that combining the original genotype data provides benefits of increased power and control over sources of heterogeneity that outweigh the difficulty and potential pitfalls of the implementation. We conducted a combined analysis using the original genotype data from 11 BP genomewide linkage scans comprising 5,179 individuals from 1,067 families. Heterogeneity among studies was minimized in our analyses by using uniform methods of analysis and a common, standardized marker map and was assessed using novel methods developed for meta-analysis of genome scans. To date, this collaboration is the largest and most comprehensive analysis of linkage samples involving a psychiatric disorder. We demonstrate that combining original genome-scan data is a powerful approach for the elucidation of linkage regions underlying complex disease. Our results establish genomewide significant linkage to BP on chromosomes 6q and 8q, which provides solid information to guide future gene-finding efforts that rely on fine-mapping and association approaches.

Inducible Enhancement of Memory Storage and Synaptic Plasticity in Transgenic Mice Expressing an Inhibitor of ATF4 (CREB-2) and C/EBP Proteins

To examine the role of C/EBP-related transcription factors in long-term synaptic plasticity and memory storage, we have used the tetracycline-regulated system and expressed in the forebrain of mice a broad dominant-negative inhibitor of C/EBP (EGFP-AZIP), which preferentially interacts with several inhibiting isoforms of C/EBP. EGFP-AZIP also reduces the expression of ATF4, a distant member of the C/EBP family of transcription factors that is homologous to the Aplysia memory suppressor gene ApCREB-2. Consistent with the removal of inhibitory constraints on transcription, we find an increase in the pattern of gene transcripts in the hippocampus of EGFP-AZIP transgenic mice and both a reversibly enhanced hippocampal-based spatial memory and LTP. These results suggest that several proteins within the C/EBP family including ATF4 (CREB-2) act to constrain long-term synaptic changes and memory formation. Relief of this inhibition lowers the threshold for hippocampal-dependent long-term synaptic potentiation and memory storage in mice.

Catechol-O-Methyltransferase (COMT) Genotypes and Working Memory: Associations with Differing Cognitive Operations

BACKGROUND Catechol-O-methyltransferase (COMT) is a strong candidate gene for schizophrenia and cognitive functions disrupted in this disorder. This report examines the relation of COMT genotypes to performance on a battery of working memory tests differing in the cognitive operations to be performed on the material. METHODS A large sample of 402 healthy adults were tested on four working memory tests: Spatial Delayed Response (SDR), Word Serial Position Test (WSPT), N-back, and Letter-Number Sequencing. A subsample (n = 246) was tested on the Wisconsin Card Sorting Test (WCST). A saliva swab was used to obtain DNA from all participants. RESULTS Letter-Number Sequencing, which requires both storage and manipulation of information, was the only working memory test that showed expected differences among COMT genotypes, with the met/met group showing the best performance and the val/val group the poorest performance. As in previous studies, the met/met group also performed better than the val/val group on the WCST. CONCLUSIONS COMT genotypes were not associated with performance on tests measuring simple storage, maintenance of temporal order or updating of information in working memory. Genotype differences in Letter-Number Sequencing and WCST suggest that higher-order components of processing (e.g., mental manipulation) are more closely related to this gene.

Evidence for Sex-Specific Risk Alleles in Autism Spectrum Disorder

We investigated the genetic aspects of the large sex bias in the prevalence of autism spectrum disorder by monitoring changes in linkage when the family set for an affected sibling pair genome scan is subdivided on the basis of the sex of affected children. This produces a significant excess in the total number of linkage peaks (P=1.3 x 10(-8)) and identifies a major male-specific linkage peak at chromosome 17q11 (P<.01). These results suggest that sexual dichotomy is an important factor in the genetics of autism; the same strategy can be used to explore this possibility in other complex disorders that exhibit significant sex biases.

Genomewide Linkage Analysis of Celiac Disease in Finnish Families

Celiac disease (CD), or gluten-sensitive enteropathy, is a common multifactorial disorder resulting from intolerance to cereal prolamins. The only established genetic susceptibility factor is HLA-DQ, which appears to explain only part of the overall genetic risk. We performed a genomewide scan of CD in 60 Finnish families. In addition to strong evidence for linkage to the HLA region at 6p21.3 (Z(max)>5), suggestive evidence for linkage was found for six other chromosomal regions--1p36, 4p15, 5q31, 7q21, 9p21-23, and 16q12. We further analyzed the three most convincing regions--4p15, 5q31, and 7q21--by evaluation of dense marker arrays across each region and by analysis of an additional 38 families. Although multipoint analysis with dense markers provided supportive evidence (multipoint LOD scores 3.25 at 4p15, 1.49 at 5q31, and 1.04 at 7q21) for the initial findings, the additional 38 families did not strengthen evidence for linkage. The role that HLA-DQ plays was studied in more detail by analysis of DQB1 alleles in all 98 families. All but one patient carried one or two HLA-DQ risk alleles, and 65% of HLA-DQ2 carriers were affected. Our study indicates that the HLA region harbors a predominant CD-susceptibility locus in these Finnish families.