Genetics of infantile seizures with paroxysmal dyskinesia: the infantile convulsions and choreoathetosis (ICCA) and ICCA-related syndromes.

The relationship between paroxysmal movement disorders (PD: paroxysmal dyskinesia) and epilepsy continues to present a challenging problem. Attacks of PD and epileptic seizures have several characteristics in common: both are paroxysmal in nature with a tendency to spontaneous remission, and a subset of PD responds well to anticonvulsants. In 1997, description of the ICCA (infantile convulsions and choreoathetosis) syndrome and linkage to chromosome 16p12-q12 provided the first genetic evidence for common mechanisms shared by benign infantile seizures and PD. The chromosome 16 ICCA locus is by far the most frequently involved in such associations as well as in pure forms of benign infantile seizures. The ICCA region at the pericentromeric area of chromosome 16 shows complicated genomic architecture and the ICCA gene still remains unknown. Genetic studies focusing on PD with or without epilepsy have led to the identification of other genes linked to chromosomes 2q35 and 10q22. Alterations of ion channel and ion pump subunits could provide a simple, albeit probably non-unique, explanation for the pathophysiology of the link between epilepsy and PD. The aim of this review is to update genetic aspects of infantile epileptic seizures and PD and their association in the context of ICCA and ICCA related syndromes.

Analysis of the dinucleotide repeat polymorphism in the epidermal growth factor receptor (EGFR) gene in head and neck cancer patients.

BACKGROUND: Epidermal growth factor receptor (EGFR) overexpression is associated with poor prognosis in head and neck cancer. The first intron of EGFR gene is polymorphic (9-23 CA repeats) and transcription declines when the number of repeats increases. PATIENTS AND METHODS: EGFR polymorphism (fluorescent genotyping) and expression (ligand-binding assay) were analyzed in tumors and normal tissues from 112 patients (100 men, 12 women; mean age 60 years). RESULTS: The number of CA repeats varied from 15 to 22. Allelic distribution was trimodal (predominance of 16, 20 and 18 CA repeats). EGFR concentrations were significantly higher (P=0.02) in homozygous tumors as compared with heterozygous. Considering homozygous tumors, or classifying genotypes as short/long/intermediary (two alleles <17 versus two alleles > or =17 versus others), no relationship was observed between tumoral EGFR genotype and expression. In the 76 tumors exhibiting at least one 16-CA allele, the length of the remaining allele was inversely correlated to EGFR expression (P=0.047). Tumoral EGFR expression, performance status (WHO criteria) and node involvement were independent predictors of specific survival (P <0.01). Tumoral or normal tissue EGFR genotype did not influence survival. CONCLUSIONS: Intron 1 EGFR polymorphism may be implicated in the regulation of EGFR expression in head and neck tumors.

PIP2 binding residues of Kir2.1 are common targets of mutations causing Andersen syndrome.

BACKGROUND: Mutations in KCNJ2, the gene encoding the inward-rectifying K+ channel Kir2.1, cause the cardiac, skeletal muscle, and developmental phenotypes of Andersen-Tawil syndrome (ATS; also known as Andersen syndrome). Although pathogenic mechanisms have been proposed for select mutations, a common mechanism has not been identified. METHODS: Seventeen probands presenting with symptoms characteristic of ATS were evaluated clinically and screened for mutations in KCNJ2. The results of mutation analysis were combined with those from previously studied subjects to assess the frequency with which KCNJ2 mutations cause ATS. RESULTS: Mutations in KCNJ2 were discovered in nine probands. These included six novel mutations (D71N, T75R, G146D, R189I, G300D, and R312C) as well as previously reported mutations R67W and R218W. Six probands possessed mutations of residues implicated in binding membrane-associated phosphatidylinositol 4,5-bisphosphate (PIP2). In total, mutations in PIP(2)-related residues accounted for disease in 18 of 29 (62%) reported KCNJ2 -based probands with ATS. Also reported is that mutation R67W causes the full clinical triad in two unrelated males. CONCLUSIONS: The novel mutations corresponding to residues involved in Kir2.1 channel-PIP2 interactions presented here as well as the overall frequency of mutations occurring in these residues indicate that defects in PIP2 binding constitute a major pathogenic mechanism of ATS. Furthermore, screening KCNJ2 in patients with the complex phenotypes of ATS was found to be invaluable in establishing or confirming a disease diagnosis as mutations in this gene can be identified in the majority of patients.

[GEFS + syndrome: phenotypic variations from the newborn to the adult in a large French pedigree]. / Syndrome GEFS +: variations phénotypiques du nourrisson à l'adulte dans une grande famille française.

The GEFS + (generalized epilepsy with febrile seizures +) syndrome was described in 1997 in a large Australian pedigree and is characterized by the familial occurrence, following an autosomal dominant transmission, of febrile convulsive seizures in infants and young children that may last beyond the age of 6, and that are associated in some with afebrile convulsive seizures and a variety of other seizures types, including typical absences, myoclo-astatic seizures, myoclonias, and focal seizures. The genetic anomalies detected to date imply either Na channels or GABA receptors. In a large French pedigree, we identified 15 patients with the GEFS + syndrome. The index patient was a 15 month-old girl with repeated convulsive febrile, afebrile and atonic seizures, who was fully controlled on valproate. Her neurologic status and development were fully normal, and the interictal EEG did not show any specific abnormality. In this pedigree, all patients had febrile seizures except two who had only afebrile seizures, two had atonic drop attacks, and tonic seizures during sleep and a single secondarily generalized focal hemifacial motor seizure were seen once each. No patient had temporal lobe seizures; they did not have myoclonias nor typical absences. The seizure profile in this family appears to be original, and the existence of yet another type of underlying genetic defect can be suspected.

Linkage of benign familial infantile convulsions to chromosome 16p12-q12 suggests allelism to the infantile convulsions and choreoathetosis syndrome.

The syndrome of benign familial infantile convulsions (BFIC) is an autosomal dominant epileptic disorder that is characterized by convulsions, with onset at age 3-12 mo and a favorable outcome. BFIC had been linked to chromosome 19q, whereas the infantile convulsions and choreoathetosis (ICCA) syndrome, in which BFIC is associated with paroxysmal dyskinesias, had been linked to chromosome 16p12-q12. BFIC appears to be frequently associated with paroxysmal dyskinesias, because many additional families from diverse ethnic backgrounds have similar syndromes that have been linked to the chromosome 16 ICCA region. Moreover, one large pedigree with paroxysmal kinesigenic dyskinesias only, has also been linked to the same genomic area. This raised the possibility that families with pure BFIC may be linked to chromosome 16 as well. We identified and studied seven families with BFIC inherited as an autosomal dominant trait. Genotyping was performed with markers at chromosome 19q and 16p12-q12. Although chromosome 19q could be excluded, evidence for linkage in the ICCA region was found, with a maximum two-point LOD score of 3.32 for markers D16S3131 and SPN. This result proves that human chromosome 16p12-q12 is a major genetic locus underlying both BFIC and paroxysmal dyskinesias. The unusual phenotype displayed by one homozygous patient suggests that variability of the ICCA syndrome could be sustained by genetic modifiers.

The genetics of human epilepsies.

INTRODUCTION: Genetic causes contribute to many different forms of human epilepsies. Genetic analyses obviously represent a very powerful tool to study this highly heterogeneous pathology. The identification of the genes involved in various epileptic syndromes could prove useful in elucidating the basic mechanisms of epilepsies. This review summarise the recent progress that have been made in the localisation and/or identification of many epilepsy genes. METHODS: The MEDLINE database as well as different other scientific sources were screened. RESULTS: While the genes responsible for several progressive epilepsies have now been identified, it is unlikely that they play a role in the aetiology of true idiopathic epilepsies. Although the majority of idiopathic epilepsies are inherited as complex traits, most studies performed to date have led to the identification of several genetic loci underlying rare epileptic syndromes inherited in a Mendelian pattern. Four genes encoding neurotransmitter- or voltage-gated ion channel subunits have been identified in various idiopathic epilepsies. The epilepsies could thus be considered as one of many paroxysmal disorders that are due to mutations in ion channel genes. CONCLUSION: Effort is still needed to identify the genes responsible for the large variety of other epileptic disorders inherited as Mendelian traits and evaluate the role of these genes in the more common and polygenic forms. Defining the genetic bases of the latter will also require that exhaustive association and sib-pair studies to be performed. These studies may help understand the pathophysiology of human epilepsies, will lead to better genetic counselling in affected families, and represent the first step towards the discovery of new therapeutic targets and methods.

Electronic identification and chromosomal assignment by radiation hybrid mapping of human expressed sequence tags corresponding to new potassium channel genes.

Human homologues of 36 Caenorhabditis elegans potassium channels were identified by expressed sequence tag (EST) database searching. This approach was combined with radiation hybrid mapping to localize new potassium channel genes in the human genome. In addition, several ESTs whose location was already known were also identified as cDNAs encoding additional potassium channels. The identification and mapping of all these genes will make them useful tools for mutation detection in neurological as well as other human diseases.

Association of infantile convulsions with paroxysmal dyskinesias (ICCA syndrome): confirmation of linkage to human chromosome 16p12-q12 in a Chinese family.

We have studied one family of Chinese origin, in which benign infantile convulsions and paroxysmal choreoathetosis (of the dystonic form) were co-inherited as a single autosomal dominant trait. This association is specific to ICCA syndrome, which we have recently described in four French families. Some patients in the new family also exhibit recurrence of epileptic seizures at a much later age, making the ICCA syndrome in this family atypical. DNA samples isolated from this family of 22 members (9 affected) have been tested with genetic markers at chromosome 16p12-q12, in which region the ICCA syndrome has previously been linked. Confirmation of linkage to this pericentromeric region of human chromosome 16 has been obtained and no critical meiotic recombination event has been detected in the ICCA region. This result suggests that, in contrast to marked clinical heterogeneity, the association of infantile convulsions with paroxysmal dyskinetic movements could be genetically homogeneous.

Recent progress in the genetics of human epilepsies.

Despite several lines of evidence indicating a strong genetic influence in the etiology of idiopathic epilepsies, progress in the mapping and identification of human epilepsy genes has been limited until recently. In addition to the localisation and/or isolation of several genes causing progressive epilepsies associated with cerebral degeneration, at least seven human genomic regions (6p, 8q, 10q, 15q, 16p, 19q, 20q) are now known to harbour genes implicated in idiopathic epilepsies. In the case of nocturnal frontal lobe epilepsy, mutations in a nicotinic acetylcholine receptor subunit gene have been identified. Systematic studies of rare epileptic disorders inherited as monogenic Mendelian traits, as well as studies on more complex polygenic idiopathic epilepsies, are still needed in order to identify all the epilepsy genes. This will allow better diagnosis and genetic counseling in families of affected individuals, a better understanding of both the pathophysiology of epilepsies and normal brain functioning, and the design of new pharmacological and genetic therapies.

Familial infantile convulsions and paroxysmal choreoathetosis: a new neurological syndrome linked to the pericentromeric region of human chromosome 16.

Benign infantile familial convulsions is an autosomal dominant disorder characterized by nonfebrile seizures, with the first attack occurring at age 3-12 mo. It is one of the rare forms of epilepsy that are inherited as monogenic Mendelian traits, thus providing a powerful tool for mapping genes involved in epileptic syndromes. Paroxysmal choreoathetosis is an involuntary-movement disorder characterized by attacks that occur spontaneously or are induced by a variety of stimuli. Classification is still elusive, and the epileptic nature of this movement disorder has long been discussed and remains controversial. We have studied four families from northwestern France in which benign infantile convulsions was inherited as an autosomal dominant trait together with variably expressed paroxysmal choreoathetosis. The human genome was screened with microsatellite markers regularly spaced, and strong evidence of linkage for the disease gene was obtained in the pericentromeric region of chromosome 16, with a maximum two-point LOD score, for D16S3133, of 6.76 at a recombination fraction of 0. Critical recombinants narrowed the region of interest to a 10-cM interval around the centromere. Our study provides the first genetic evidence for a common basis of convulsive and choreoathetotic disorders and will help in the understanding and classification of paroxysmal neurological syndromes.

Framework YAC contig anchored into a 3.2-Mb high-resolution physical map in proximal 11q13.

Despite the presence on band q13 of chromosome 11 of a number of genes predisposing individuals to various human diseases, most of this genomic region remains loosely mapped. Moreover, there is a relative dearth of yeast artificial chromosome (YAC) contigs from genome-wide studies: YACs are irregularly distributed over this chromosomal region and have not been arranged into contigs. We have thus undertaken fine-scale mapping of a 3.2-Mb region flanked by ACTN3 and FGF3. Since this region has demonstrated a high degree of YAC instability, we have established a framework contig by anchoring YACs and cosmids into a high-resolution physical map based on fluorescence in situ hybridization and long-range restriction mapping. The 3.2-Mb area studied includes the boundaries of regions thought to contain genes predisposing individuals to osteoporosis-pseudoglioma syndrome and insulin-dependent diabetes mellitus, as well as genes driving amplification events in human carcinomas. Another feature of this genomic area is that it cross-hybridizes to nonsyntenic regions of the genome. In addition, it spans the region where syntenic conservation with mouse chromosome 19 ends, making clones that we have anchored there valuable tools in understanding genome evolution.

Metaphase and interphase mapping by FISH: improvement of chromosome banding and signal resolution in interphase nuclei by means of iterative deconvolution.

FISH images obtained with conventional epifluorescence microscopes are always blurred by glare and out of focus light emissions. In order to restore high contrast images, a procedure based on a modelling of the optical system in the microscope was developed and used for the processing of images acquired with a cooled CCD camera mounted on a fluorescence microscope. This procedure was tested on images of both mouse and human chromosomes stained with DAP1 and on images of interphase nuclei hybridized with pairs of cosmid probes. This method improves the definition and the sharpness of the DAPI G-banding and thus facilitates and speeds up the identification of chromosomes. When performed on images of interphase cell nuclei, this procedure allows the discrimination of fluorescent signals which appear partially overlapping on raw images. This significant improvement of spatial resolution is of particular interest for ordering sets of probes on DNA fibers.

Description of a 700-kb yeast artificial chromosome contig containing the BCL1 translocation breakpoint region at 11q13.

We screened two human yeast artificial chromosome (YAC) libraries by polymerase chain reaction (PCR) with oligonucleotides specific to the BCL1 major translocation breakpoint cluster region at 11q13. Five YACs were isolated. Two of them were chimeric. One of these and remaining three YACs were characterized by hybridization with various known 11q13 probes, Alu-PCR fingerprinting, in situ hybridization, and isolation of YAC ends. A map of this ca 700-kb YAC contig was obtained. This map was consistent with maps established from total human genomic DNA. Every YAC in this region was found unstable and gave rise to reproducibly deleted lineages. Analysis in detail of these deletions over many generations showed that more than a single sequence might be involved. The availability of cloned material will facilitate the search for the still elusive genetic elements responsible for amplifications, deletions and translocations observed at 11q13 in malignancies.

Mapping genes according to their amplification status in tumor cells: contribution to the map of 11q13.

DNA amplification events that occur at 11q13 in human carcinomas are complex, and amplicons were shown to exhibit numerous discontinuities that could be used as tools for mapping this genomic area. A statistical nearest-neighbor analysis of the amplification patterns of several 11q13 loci in a panel of amplified DNAs was performed in the region of 11q13 centromeric from BCL1. It was strongly correlated with the physical linkages that we established between the same markers. Taken together, our results led to a map of 14 genes and four anonymous probes located in this area.

DNA amplification at 11q13.5-q14 in human breast cancer.

Band q13 of chromosome 11 is frequently amplified in human breast cancers, but the gene(s) responsible for the emergence of this amplicon remain(s) elusive as yet. As a tribute to the complexity of the amplification events involving 11q13 sequences in human breast cancer, we have now studied a more telomeric region at 11q13.5-q14 defined by a new transcription unit, D11S833E. We have observed that amplicons present in cell lines and primary tumors amplified for both BCL1 and D11S833E could be interrupted between these two loci. Such discontinuities were demonstrated by using a probe for the KRN1 gene, which we have localized between the BCL1/FGF4 region and D11S833E. In fact, KRN1 was not present in 4 out of 10 amplicons bearing both BCL1 and D11S833E. Furthermore, we have observed tumors in which D11S833E could be amplified in the absence of amplification of other known markers of 11q13. Therefore, D11S833E defines a new and independent amplification unit in this region.