A patient with homozygous nonsense variants in two Leigh syndrome disease genes: Distinguishing a dual diagnosis from a hypomorphic protein-truncating variant.

Leigh syndrome is a mitochondrial disease caused by pathogenic variants in over 85 genes. Whole exome sequencing of a patient with Leigh-like syndrome identified homozygous protein-truncating variants in two genes associated with Leigh syndrome; a reported pathogenic variant in PDHX (NP_003468.2:p.(Arg446*)), and an uncharacterized variant in complex I (CI) assembly factor TIMMDC1 (NP_057673.2:p.(Arg225*)). The TIMMDC1 variant was predicted to truncate 61 amino acids at the C-terminus and functional studies demonstrated a hypomorphic impact of the variant on CI assembly. However, the mutant protein could still rescue CI assembly in TIMMDC1 knockout cells and the patient's clinical phenotype was not clearly distinct from that of other patients with the same PDHX defect. Our data suggest that the hypomorphic effect of the TIMMDC1 protein-truncating variant does not constitute a dual diagnosis in this individual. We recommend cautious assessment of variants in the C-terminus of TIMMDC1 and emphasize the need to consider the caveats detailed within the American College of Medical Genetics and Genomics (ACMG) criteria when assessing variants.

Transcriptome-wide effects of a POLR3A gene mutation in patients with an unusual phenotype of striatal involvement.

RNA polymerase III is essential for the transcription of non-coding RNAs, including tRNAs. Mutations in the genes encoding its largest subunits are known to cause hypomyelinating leukodystrophies (HLD7) with pathogenetic mechanisms hypothesised to involve impaired availability of tRNAs. We have identified a founder mutation in the POLR3A gene that leads to aberrant splicing, a premature termination codon and partial deficiency of the canonical full-length transcript. Our clinical and imaging data showed no evidence of the previously reported white matter or cerebellar involvement; instead the affected brain structures included the striatum and red nuclei with the ensuing clinical manifestations. Our transcriptome-wide investigations revealed an overall decrease in the levels of Pol III-transcribed tRNAs and an imbalance in the levels of regulatory ncRNAs such as small nuclear and nucleolar RNAs (snRNAs and snoRNAs). In addition, the Pol III mutation was found to exert complex downstream effects on the Pol II transcriptome, affecting the general regulation of RNA metabolism.

Integrin alpha 8 recessive mutations are responsible for bilateral renal agenesis in humans.

Renal hypodysplasia (RHD) is a heterogeneous condition encompassing a spectrum of kidney development defects including renal agenesis, hypoplasia, and (cystic) dysplasia. Heterozygous mutations of several genes have been identified as genetic causes of RHD with various severity. However, these genes and mutations are not associated with bilateral renal agenesis, except for RET mutations, which could be involved in a few cases. The pathophysiological mechanisms leading to total absence of kidney development thus remain largely elusive. By using a whole-exome sequencing approach in families with several fetuses with bilateral renal agenesis, we identified recessive mutations in the integrin α8-encoding gene ITGA8 in two families. Itga8 homozygous knockout in mice is known to result in absence of kidney development. We provide evidence of a damaging effect of the human ITGA8 mutations. These results demonstrate that mutations of ITGA8 are a genetic cause of bilateral renal agenesis and that, at least in some cases, bilateral renal agenesis is an autosomal-recessive disease.

Autosomal-recessive congenital cerebellar ataxia is caused by mutations in metabotropic glutamate receptor 1.

Autosomal-recessive congenital cerebellar ataxia was identified in Roma patients originating from a small subisolate with a known strong founder effect. Patients presented with global developmental delay, moderate to severe stance and gait ataxia, dysarthria, mild dysdiadochokinesia, dysmetria and tremors, intellectual deficit, and mild pyramidal signs. Brain imaging revealed progressive generalized cerebellar atrophy, and inferior vermian hypoplasia and/or a constitutionally small brain were observed in some patients. Exome sequencing, used for linkage analysis on extracted SNP genotypes and for mutation detection, identified two novel (i.e., not found in any database) variants located 7 bp apart within a unique 6q24 linkage region. Both mutations cosegregated with the disease in five affected families, in which all ten patients were homozygous. The mutated gene, GRM1, encodes metabotropic glutamate receptor mGluR1, which is highly expressed in cerebellar Purkinje cells and plays an important role in cerebellar development and synaptic plasticity. The two mutations affect a gene region critical for alternative splicing and the generation of receptor isoforms; they are a 3 bp exon 8 deletion and an intron 8 splicing mutation (c.2652_2654del and c.2660+2T>G, respectively [RefSeq accession number NM_000838.3]). The functional impact of the deletion is unclear and is overshadowed by the splicing defect. Although ataxia lymphoblastoid cell lines expressed GRM1 at levels comparable to those of control cells, the aberrant transcripts skipped exon 8 or ended in intron 8 and encoded various species of nonfunctional receptors either lacking the transmembrane domain and containing abnormal intracellular tails or completely missing the tail. The study implicates mGluR1 in human hereditary ataxia. It also illustrates the potential of the Roma founder populations for mutation identification by exome sequencing.

Founder p.Arg 446* mutation in the PDHX gene explains over half of cases with congenital lactic acidosis in Roma children.

Investigation of 31 of Roma patients with congenital lactic acidosis (CLA) from Bulgaria identified homozygosity for the R446* mutation in the PDHX gene as the most common cause of the disorder in this ethnic group. It accounted for around 60% of patients in the study and over 25% of all CLA cases referred to the National Genetic Laboratory in Bulgaria. The detection of a homozygous patient from Hungary and carriers among population controls from Romania and Slovakia suggests a wide spread of the mutation in the European Roma population. The clinical phenotype of the twenty R446* homozygotes was relatively homogeneous, with lactic acidosis crisis in the first days or months of life as the most common initial presentation (15/20 patients) and delayed psychomotor development and/or seizures in infancy as the leading manifestations in a smaller group (5/20 patients). The subsequent clinical picture was dominated by impaired physical growth and a very consistent pattern of static cerebral palsy-like encephalopathy with spasticity and severe to profound mental retardation seen in over 80% of cases. Most patients had a positive family history. We propose testing for the R446* mutation in PDHX as a rapid first screening in Roma infants with metabolic acidosis. It will facilitate and accelerate diagnosis in a large proportion of cases, allow early rehabilitation to alleviate the chronic clinical course, and prevent further affected births in high-risk families.

Partial deficiency of the C-terminal-domain phosphatase of RNA polymerase II is associated with congenital cataracts facial dysmorphism neuropathy syndrome.

Congenital cataracts facial dysmorphism neuropathy (CCFDN) syndrome (OMIM 604168) is an autosomal recessive developmental disorder that occurs in an endogamous group of Vlax Roma (Gypsies; refs. 1-3). We previously localized the gene associated with CCFDN to 18qter, where a conserved haplotype suggested a single founder mutation. In this study, we used recombination mapping to refine the gene position to a 155-kb critical interval. During haplotype analysis, we found that the non-transmitted chromosomes of some unaffected parents carried the conserved haplotype associated with the disease. Assuming such parents to be completely homozygous across the critical interval except with respect to the disease-causing mutation, we developed a new 'not quite identical by descent' (NQIBD) approach, which allowed us to identify the mutation causing the disease by sequencing DNA from a single unaffected homozygous parent. We show that CCFDN is caused by a single-nucleotide substitution in an antisense Alu element in intron 6 of CTDP1 (encoding the protein phosphatase FCP1, an essential component of the eukaryotic transcription machinery), resulting in a rare mechanism of aberrant splicing and an Alu insertion in the processed mRNA. CCFDN thus joins the group of 'transcription syndromes' and is the first 'purely' transcriptional defect identified that affects polymerase II-mediated gene expression.

Impact of the Reelin signaling cascade (ligands-receptors-adaptor complex) on cognition in schizophrenia.

Our previous neurocognitive studies of schizophrenia outlined two clusters of affected subjects--cognitively spared (CS) and cognitive deficit (CD), the latter's characteristics pointing to developmental origins and impaired synaptic plasticity. Here we investigate the contribution of polymorphisms in major regulators of these processes to susceptibility to schizophrenia and to CD in patients. We examine variation in genes encoding proteins at the gateway of Reelin signaling: ligands RELN and APOE, their common receptors APOER2 and VLDLR, and adaptor DAB1. Association analysis with disease outcome and cognitive performance in the Western Australian Family Study of Schizophrenia (WAFSS) was followed by replication analysis in the Australian Schizophrenia Research Bank (ASRB) and in the Health in Men Study (HIMS) of normal aging males. In the WAFSS sample, we observed significant association of APOE, APOER2, VLDLR, and DAB1 SNPs with disease outcome in the case-control and CD-control datasets, and with pre-morbid intelligence and verbal memory in cases. HIMS replication analysis supported rs439401 (APOE regulatory region), and rs2297660 and rs3737983 (APOER2), with an effect on memory performance in normal aging subjects consistent with the findings in schizophrenia cases. APOER2 gene expression analysis revealed lower transcript levels in lymphoblastoid cells from cognitively impaired schizophrenia patients of the alternatively spliced exon 19, mediating Reelin signaling and synaptic plasticity in the adult brain. ASRB replication analysis produced marginally significant results, possibly reflecting a recruitment strategy biased toward CS patients. The data suggest a contribution of neurodevelopmental/synaptic plasticity genes to cognitive impairment in schizophrenia.

Partial epilepsy syndrome in a Gypsy family linked to 5q31.3-q32.

PURPOSE: The restricted genetic diversity and homogeneous molecular basis of Mendelian disorders in isolated founder populations have rarely been explored in epilepsy research. Our long-term goal is to explore the genetic basis of epilepsies in one such population, the Gypsies. The aim of this report is the clinical and genetic characterization of a Gypsy family with a partial epilepsy syndrome. METHODS: Clinical information was collected using semistructured interviews with affected subjects and informants. At least one interictal electroencephalography (EEG) recording was performed for each patient and previous data obtained from records. Neuroimaging included structural magnetic resonance imaging (MRI). Linkage and haplotype analysis was performed using the Illumina IVb Linkage Panel, supplemented with highly informative microsatellites in linked regions and Affymetrix SNP 5.0 array data. RESULTS: We observed an early-onset partial epilepsy syndrome with seizure semiology strongly suggestive of temporal lobe epilepsy (TLE), with mild intellectual deficit co-occurring in a large proportion of the patients. Psychiatric morbidity was common in the extended pedigree but did not cosegregate with epilepsy. Linkage analysis definitively excluded previously reported loci, and identified a novel locus on 5q31.3-q32 with an logarithm of the odds (LOD) score of 3 corresponding to the expected maximum in this family. DISCUSSION: The syndrome can be classified as familial temporal lobe epilepsy (FTLE) or possibly a new syndrome with mild intellectual deficit. The linked 5q region does not contain any ion channel-encoding genes and is thus likely to contribute new knowledge about epilepsy pathogenesis. Identification of the mutation in this family and in additional patients will define the full phenotypic spectrum.

The longevity gene Klotho is differentially associated with cognition in subtypes of schizophrenia.

Cognitive impairment is a core feature of schizophrenia and impacts negatively the functioning of affected individuals. Cognitive decline correlates with aging, and is the primary cause of loss of independence and reduced quality of life. The klotho gene is a key modulator of aging, with expression deficiency resulting in premature aging, while overexpression extends lifespan and enhances cognition. A haplotype and functional human variant of the gene, KL-VS, increases expression and promotes longevity. KL-VS heterozygosity is associated with enhanced cognition and a larger volume of the right dorsolateral prefrontal cortex, a region involved in planning and decision-making, which is especially susceptible to shrinkage with age. We examined the effect of KL-VS heterozygosity on cognition in 497 schizophrenia patients and 316 healthy controls from the Western Australian Family Study of Schizophrenia (WAFSS) who had been comprehensively characterised by neurocognitive tests and classified into cognitively deficient (CD) and cognitively "spared" (CS) clusters. An older, cognitively normal population sample from the Health in Men Study (HIMS) was included to allow assessment of heterozygosity and memory in aged individuals. We show that heterozygosity is associated with better learning and memory in the younger WAFSS healthy controls but not in the aging HIMS sample. However, in schizophrenia patients, KL-VS has a selective effect on memory, with heterozygotes in CD and CS clusters performing worse than non-carriers. This effect was significant and more severe in the CD cluster, reinforcing the utility of subtyping patients into CD and CS clusters that may differ in their genetic underpinnings.

Whole genome sequencing of 91 multiplex schizophrenia families reveals increased burden of rare, exonic copy number variation in schizophrenia probands and genetic heterogeneity.

The importance of genomic copy number variants (CNVs) has long been recognized in the etiology of neurodevelopmental diseases. We report here the results from the CNV analysis of whole-genome sequences from 91 multiplex schizophrenia families. Employing four algorithms (CNVnator, Cn.mops, DELLY and LUMPY) to identify CNVs, we find 1231 rare deletions and 287 rare duplications in 300 individuals (77 with schizophrenia (SZ), 32 with schizoaffective disorder (SAD), 82 with another neuropsychiatric diagnosis and 109 unaffected). The size of the CNVs ranges from a few hundred base-pairs to about 1.3Mb. The total burden of CNVs does not differ significantly between affected (SZ and SAD) and unaffected individuals. Parent-to-child transmission rate for rare CNVs affecting exonic regions is significantly higher for affected (SZ and SAD) probands as compared to their siblings, but rates for all CNVs is not. We observe heterogeneity between families in terms of genes involved in CNVs, and find several CNVs involving genes previously implicated in either schizophrenia or other neuropsychiatric disorders.

A Roma founder BIN1 mutation causes a novel phenotype of centronuclear myopathy with rigid spine.

OBJECTIVE: To describe a large series of BIN1 patients, in which a novel founder mutation in the Roma population of southern Spain has been identified. METHODS: Patients diagnosed with centronuclear myopathy (CNM) at 5 major reference centers for neuromuscular disease in Spain (n = 53) were screened for BIN1 mutations. Clinical, histologic, radiologic, and genetic features were analyzed. RESULTS: Eighteen patients from 13 families carried the p.Arg234Cys variant; 16 of them were homozygous for it and 2 had compound heterozygous p.Arg234Cys/p.Arg145Cys mutations. Both BIN1 variants have only been identified in Roma, causing 100% of CNM in this ethnic group in our cohort. The haplotype analysis confirmed all families are related. In addition to clinical features typical of CNM, such as proximal limb weakness and ophthalmoplegia, most patients in our cohort presented with prominent axial weakness, often associated with rigid spine. Severe fat replacement of paravertebral muscles was demonstrated by muscle imaging. This phenotype seems to be specific to the p.Arg234Cys mutation, not reported in other BIN1 mutations. Extreme clinical variability was observed in the 2 compound heterozygous patients for the p.Arg234Cys/p.Arg145Cys mutations, from a congenital onset with catastrophic outcome to a late-onset disease. Screening of European Roma controls (n = 758) for the p.Arg234Cys variant identified a carrier frequency of 3.5% among the Spanish Roma. CONCLUSION: We have identified a BIN1 founder Roma mutation associated with a highly specific phenotype, which is, from the present cohort, the main cause of CNM in Spain.

Longevity Klotho gene polymorphism and the risk of dementia in older men.

INTRODUCTION: Klotho variants (KL-VS) have been associated with increased longevity and better cognitive function. It is unclear whether they modulate dementia risk. METHODS: We recruited 527 men aged 71-87 years who were free of cognitive impairment. We used data linkage to track the onset of dementia over 10 years. KL-VS genotyping (rs9536314 T/G) followed standard procedures. RESULTS: The annual rate of dementia was 17.2‰ (95%CI=14.0-21.1; total=5053 person-years), and 14.0‰ (95%CI=10.6-18.4; 3582 person-years), 23.5‰ (95%CI=16.6-33.2; 1363 person-years) and 46.4‰ (95%CI=19.3-111.5; 108 person-years) for men with the TT, TG and GG genotypes. Compared with the TT genotype, the sub-hazard ratios of dementia associated with the TG and GG genotypes were 1.6 (95%CI=1.0, 2.5; p=0.030) and 3.5 (95%CI=1.3, 9.1; p=0.011). DISCUSSION: The Klotho KL-VS variant is associated with an increase in the incidence of dementia in older men, in a dose-dependent fashion (intermediate for heterozygosis and highest for homozygosis).

Exome array analysis suggests an increased variant burden in families with schizophrenia.

The exome array assays rare-but-recurrent, likely deleterious, exonic variants and represents an intermediary between single nucleotide polymorphism (SNP) arrays and sequencing for genetic association studies. Multiplex families with multiple affected individuals may be enriched for disease-associated variants of this class compared to unrelated populations. We present an exome array study of schizophrenia in 99 multiplex families (n=341, including 118 cases) from the Western Australian Family Study of Schizophrenia (WAFSS). Compared to 55,726 individuals from the DIAGRAM sample not selected for schizophrenia, overall allele frequency of exome variants was higher in the WAFSS (P<2.2E-16). This was pronounced in variants nominally associated (P<0.05) with schizophrenia. Genes harbouring variants present only in WAFSS cases were enriched (FDR-corrected P=0.05) for membership of the 'extracellular matrix (ECM) - receptor interaction' biological pathway, adding to evidence that processes affecting the composition or turnover of ECM may contribute to neuropsychiatric disease. We did not find individual variants significantly associated with schizophrenia, although like previous studies, power to detect associations of small effect size was low. Cases did not exhibit a higher burden of variants compared to their unaffected relatives and the finding of previous exome chip studies of unrelated samples that 'schizophrenia gene-sets' were enriched for case-only variants was not replicated in the WAFSS. The higher frequency of moderately rare, exonic variants in these multiplex families compared to a population-based sample may account for some of their genetic liability to schizophrenia, and adds to evidence for a role of exome array variants from previous studies of unrelated samples.

UFM1 founder mutation in the Roma population causes recessive variant of H-ABC.

OBJECTIVE: To identify the gene defect in patients with hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) who are negative for TUBB4A mutations. METHODS: We performed homozygosity mapping and whole exome sequencing (WES) to detect the disease-causing variant. We used a Taqman assay for population screening. We developed a luciferase reporter construct to investigate the effect of the promoter mutation on expression. RESULTS: Sixteen patients from 14 families from different countries fulfilling the MRI criteria for H-ABC exhibited a similar, severe clinical phenotype, including lack of development and a severe epileptic encephalopathy. The majority of patients had a known Roma ethnic background. Single nucleotide polymorphism array analysis in 5 patients identified one large overlapping homozygous region on chromosome 13. WES in 2 patients revealed a homozygous deletion in the promoter region of UFM1. Sanger sequencing confirmed homozygosity for this variant in all 16 patients. All patients shared a common haplotype, indicative of a founder effect. Screening of 1,000 controls from different European Roma panels demonstrated an overall carrier rate of the mutation of 3%-25%. Transfection assays showed that the deletion significantly reduced expression in specific CNS cell lines. CONCLUSIONS: UFM1 encodes ubiquitin-fold modifier 1 (UFM1), a member of the ubiquitin-like family involved in posttranslational modification of proteins. Its exact biological role is unclear. This study associates a UFM1 gene defect with a disease and sheds new light on possible UFM1 functional networks.

Integrity of genome-wide genotype data from low passage lymphoblastoid cell lines.

We compared genotype data from the HumanExomeCore Array in peripheral blood mononuclear cells and low passage lymphoblastoid cell lines from the same 24 individuals to test for genotypic errors caused by the Epstein-Barr Virus transformation process. Genotype concordance across the 24 comparisons was 99.57% for unfiltered genotype data, and 99.63% following standard genotype quality control filters. Mendelian error rates and levels of heterozygosity were not significantly different between lymphoblastoid cell lines and their parent peripheral blood mononuclear cells. These results show that at low passage numbers, genotype discrepancies are minimal even before stringent quality control, and extend current evidence qualifying the use of low-passage lymphoblastoid cell lines as a reliable DNA source for genotype analysis.

Mutation screening of the N-myc downstream-regulated gene 1 (NDRG1) in patients with Charcot-Marie-Tooth Disease.

In a previous study, we have shown that N-myc downstream-regulated gene 1 (NDRG1), classified in databases as a tumor suppressor and heavy metal-response protein, is mutated in hereditary motor and sensory neuropathy Lom (HMSNL), a severe autosomal recessive form of Charcot-Marie-Tooth (CMT) disease. The private founder mutation R148X, causing HMSNL in patients of Romani ethnicity, has so far remained the only molecular defect linking NDRG1 to a specific disease phenotype. Here we report the first study aiming to assess the overall contribution of this gene to the pathogenesis of peripheral neuropathies, in cases where the most common causes of CMT disease have been excluded. Sequence analysis of NDRG1 in 104 CMT patients of diverse ethnicity identified one novel disease-causing mutation, IVS8-1G>A (g.2290787G>A), which affects the splice-acceptor site of IVS8 and results in the skipping of exon 9. The phenotype of the IVS8-1G>A homozygote was very closely related to that of HMSNL patients. In addition, we have detected homozygosity for the known R148X mutation in two affected individuals. Mutations in NDRG1 thus accounted for 2.88% of our overall group of patients, and for 4.68% of cases with demyelinating neuropathies. No other variants were identified in the coding sequence, whereas 12 single nucleotide polymorphisms were observed in the introns. Hum Mutat 22:129-135, 2003.

Genealogy and genes: tracing the founding fathers of Tristan da Cunha.

The island population of Tristan da Cunha has a well-documented genealogy that dates to its first permanent settlement in 1816. The current population is thought to have descended from only seven females and eight males. Today, there are seven family names in use, corresponding to the number of founding fathers with present-day male descendents. Y chromosome polymorphisms have previously been shown to be reliable tools for tracing patrilineal genealogies. Here, we studied Y chromosome polymorphisms in a sample from Tristan da Cunha together with genealogical records to (i) infer the haplotypes of the seven founders and (ii) test if the Y chromosome transmission is consistent with the documented patrilineal history of the island community. We observed nine Y chromosome haplotypes of which seven could be traced to the known ancestors. Of the two additional lineages, one probably evolved from a founder haplotype due to a single-step microsatellite mutation, while the other had an obvious non-island origin. Its introduction, however, is not reflected in the records. Four more instances of non-paternity were identified, with the "new" chromosomes matching other island haplotypes. The Y chromosome data presented here question the validity of some of the genealogical documentation and emphasise the value of genetic studies in tracing ancestry.

Deleterious GRM1 mutations in schizophrenia.

We analysed a phenotypically well-characterised sample of 450 schziophrenia patients and 605 controls for rare non-synonymous single nucleotide polymorphisms (nsSNPs) in the GRM1 gene, their functional effects and family segregation. GRM1 encodes the metabotropic glutamate receptor 1 (mGluR1), whose documented role as a modulator of neuronal signalling and synaptic plasticity makes it a plausible schizophrenia candidate. In a recent study, this gene was shown to harbour a cluster of deleterious nsSNPs within a functionally important domain of the receptor, in patients with schizophrenia and bipolar disorder. Our Sanger sequencing of the GRM1 coding regions detected equal numbers of nsSNPs in cases and controls, however the two groups differed in terms of the potential effects of the variants on receptor function: 6/6 case-specific and only 1/6 control-specific nsSNPs were predicted to be deleterious. Our in-vitro experimental follow-up of the case-specific mutants showed that 4/6 led to significantly reduced inositol phosphate production, indicating impaired function of the major mGluR1 signalling pathway; 1/6 had reduced cell membrane expression; inconclusive results were obtained in 1/6. Family segregation analysis indicated that these deleterious nsSNPs were inherited. Interestingly, four of the families were affected by multiple neuropsychiatric conditions, not limited to schizophrenia, and the mutations were detected in relatives with schizophrenia, depression and anxiety, drug and alcohol dependence, and epilepsy. Our findings suggest a possible mGluR1 contribution to diverse psychiatric conditions, supporting the modulatory role of the receptor in such conditions as proposed previously on the basis of in vitro experiments and animal studies.

Focal epilepsy of probable temporal lobe origin in a Gypsy family showing linkage to a novel locus on 7p21.3.

We aimed to characterise the phenotype and perform genetic studies in a family of Roma/Gypsy ethnicity, affected by epilepsy. The mean age at onset of epilepsy was 9 years and seizures persisted into adulthood. Antecedent febrile convulsions were rare. Seizure semiology and EEG findings suggested mesial temporal lobe origin with no evidence of hippocampal sclerosis. Seizures frequently generalised. Family structure suggested autosomal-dominant inheritance with incomplete penetrance. Linkage analysis identified a single novel locus on 7p21.3, corresponding to the expected maximum in the family. Previously reported temporal lobe epilepsy (TLE) loci were definitely excluded. The minimal shared haplotype of 2.4cM (1.3Mb) was not observed in other affected families or controls from the same population. Three brain-expressed validated genes in the critical region represent potential candidates. We have identified an epilepsy syndrome with temporal lobe seizures commonly evolving to generalised convulsions. Linkage to 7p21.3 adds up to a total of five currently known FTLE loci.