Febrile seizures affect approximately 3% of all children under six years of age and are by far the most common seizure disorder. A small proportion of children with febrile seizures later develop ongoing epilepsy with afebrile seizures. Segregation analysis suggests the majority of cases have complex inheritance but rare families show apparent autosomal dominant inheritance. Two putative loci have been mapped (FEB1 and FEB2), but specific genes have not yet been identified. We recently described a clinical subset, termed generalized epilepsy with febrile seizures plus (GEFS+), in which many family members have seizures with fever that may persist beyond six years of age or be associated with afebrile generalized seizures. We now report linkage, in another large GEFS+ family, to chromosome region 19q13.1 and identification of a mutation in the voltage-gated sodium (Na+)-channel beta1 subunit gene (SCN1B). The mutation changes a conserved cysteine residue disrupting a putative disulfide bridge which normally maintains an extracellular immunoglobulin-like fold. Co-expression of the mutant beta1 subunit with a brain Na+-channel alpha subunit in Xenopus laevis oocytes demonstrates that the mutation interferes with the ability of the subunit to modulate channel-gating kinetics consistent with a loss-of-function allele. This observation develops the theme that idiopathic epilepsies are a family of channelopathies and raises the possibility of involvement of other Na+-channel subunit genes in febrile seizures and generalized epilepsies with complex inheritance patterns.

The nature of subtypes in schizophrenia and the meaning of heterogeneity in schizophrenia have been considered a principal controversy in psychiatric research. We addressed these issues in periodic catatonia, a clinical entity derived from Leonhard's classification of schizophrenias, in a genomewide linkage scan. Periodic catatonia is characterized by qualitative psychomotor disturbances during acute psychotic outbursts and by long-term outcome. On the basis of our previous findings of a lifetime morbidity risk of 26.9% of periodic catatonia in first-degree relatives, we conducted a genome scan in 12 multiplex pedigrees with 135 individuals, using 356 markers with an average spacing of 11 cM. In nonparametric multipoint linkage analyses (by GENEHUNTER-PLUS), significant evidence for linkage was obtained on chromosome 15q15 (P = 2.6 x 10(-5); nonparametric LOD score [LOD*] 3.57). A further locus on chromosome 22q13 with suggestive evidence for linkage (P = 1.8 x 10(-3); LOD* 1.85) was detected, which indicated genetic heterogeneity. Parametric linkage analysis under an autosomal dominant model (affecteds-only analysis) provided independent confirmation of nonparametric linkage results, with maximum LOD scores 2.75 (recombination fraction [theta].04; two-point analysis) and 2.89 (theta =.029; four-point analysis), at the chromosome 15q candidate region. Splitting the complex group of schizophrenias on the basis of clinical observation and genetic analysis, we identified periodic catatonia as a valid nosological entity. Our findings provide evidence that periodic catatonia is associated with a major disease locus, which maps to chromosome 15q15.

Epidermolytic palmoplantar keratoderma (EPPK) (Vörner-Unna-Thost) is an autosomal dominantly inherited skin disease of unknown etiology characterized by diffuse severe hyperkeratosis of the palms and soles and, histologically, by cellular degeneration. We have mapped a gene for EPPK to chromosome 17q11-q23, with linkage analysis using microsatellite DNA-polymorphisms, in a single large family of 7 generations. A maximum lod score of z = 6.66 was obtained with the probe D17S579 at a recombination fraction of theta = 0.00. This locus maps to the same region as the type I (acidic) keratin gene cluster. Keratins, members of the intermediate filament family, the major proteins of the cytoskeleton in epidermis, are differentially expressed in a tissue-specific manner. One acidic keratin, keratin 9 (KRT9), is expressed only in the terminally differentiated epidermis of palms and soles. The KRT9 gene has not yet been cloned; however, since the genes for most acidic keratins are clustered, it is highly probable that it too will map to this region. We therefore propose KRT9 as the candidate gene for EPPK.

Papillon-Lefèvre syndrome is an autosomal recessively inherited palmoplantar keratoderma of unknown aetiology associated with severe periodontitis leading to premature loss of dentition. Three consanguineous families, two of Turkish and one of German origin, and three multiplex families, one of Ethiopian and two of German origin, with 11 affected and 6 unaffected siblings in all were studied. A targeted genome search was initially attempted to several candidate gene regions but failed to demonstrate linkage. Therefore a genome-wide linkage scan using a combination of homozygosity mapping and traditional linkage analysis was undertaken. Linkage was obtained with marker D11S937 with a maximum two-point lod score of Zmax = 6.1 at recombination fraction theta = 0.00 on chromosome 11q14-q21 near the metalloproteinase gene cluster. Multipoint likelihood calculations gave a maximum lod score of 7.35 between D11S901 and D11S1358. A 9.2-cM region homozygous by descent in the affected members of the three consanguineous families lies between markers D11S1989 and D11S4176 harbouring the as yet unknown Papillon-Lefèvre syndrome gene. Haplotype analyses in all the families studied support this localisation. This study has identified a further locus harbouring a gene for palmoplantar keratoderma and one possibly involved in periodontitis.

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Mutations in the human keratin 9 gene have recently been shown to be involved in the etiology of palmoplantar keratoderma (PPK). We have investigated eleven unrelated German kindreds with the epidermolytic variant of PPK (EPPK) for mutations in the keratin 9 gene. We have identified two novel mutations, M156V and Q171P, both in the coil 1A segment of keratin 9. Mutation M156V was detected in two unrelated patients with EPPK, and mutation Q171P was shown to cosegregate with the disease in a large four-generation family. These findings confirm the functional importance of coil 1A integrity for heterodimerisation in keratins and for intermediate filament assembly. Our results provide further evidence for mutational heterogeneity in EPPK, and for the involvement of keratins in diseases of hyperkeratinisation and epidermolysis.

We have completely sequenced the introns of the human L-type pyruvate kinase (PK) gene using the published cDNA sequence. Subsequently, DNA from 12 unrelated PK deficiency (PKD) patients of Central European origin was investigated for mutations in this gene by solid-phase sequencing. We detected 10 different mutations, 9 of which result in single amino acid alterations, whereas the tenth destroys a splice site. Eight of the 10 mutations have not been described before. We found 7 missense mutations: G994-->A (Gly-332-->Ser), G1006-->T (Ala- 336-->Ser), A1081-->G (Asn-361-->Asp), G1174-->A (Ala-392-->Thr), G1493- ->A (Arg-498-->His), G1529-->A (Arg-510-->Gln), C1594-->T (Arg-532-- >Trp), one in-frame triplet deletion (del) as well as one insertion (ins): del AAG1060–62 (del Lys-354), ins AGC after C1203 (ins Ser after Cys-401), and one splice-site mutation at the border of intron A to exon 3: g/G283-->a/G. Although the enzymatic properties are substantially changed in all PK mutations, only two affected amino acid positions are in or close to the active site. Mutations C1594-->T, G994- ->A, del AAG1060–62 and the splice-site mutation g/G283-->a/G have been detected in two different patients each. Mutation G1529-->A was found in five different alleles. Haplotype analysis with the A/C polymorphism at position 1705 gave evidence for a single origin of this most frequent mutation in PKD as suggested by Baronciani and Beutler (Proc Natl Acad Sci USA 90:4324, 1993). Carrier detection and prenatal diagnosis are now feasible for the affected families.

Angelman syndrome (AS) is a relatively frequent disorder of psychomotor development caused by loss of function of a gene from chromosome 15q11-q13, a region subject to genomic imprinting. The AS gene(s) is exclusively expressed from the maternal chromosome. Several kinds of mutations have been found to cause AS. More than half of the cases exhibit a deletion of the maternal 15q11-q13 region. Recently, we and others described a new mutation type, the imprinting mutation, characterised by normal, biparental inheritance but aberrant methylation patterns of the entire chromosomal region. In AS, a paternal imprint is found on the maternal chromosome probably leading to functional inactivation of the AS gene(s). We have now compared the phenotype of 9 AS patients with imprinting mutation to that of nine age-matched ones with a maternally derived deletion. Both groups were evaluated for 19 common AS symptoms. All patients, independently of their molecular findings, showed classical AS symptoms such s mental retardation, delayed motor development, and absent speech. In contrast, for two signs, hypopigmentation and microcephaly, a different distribution among both groups was observed. Only one of nine AS patients with an imprinting mutation, but seven of nine in the deletion control group showed either symptom. Our results suggest that imprinting mutations, in contrast to deletions, cause only incomplete loss of gene function or that maternally derived deletions affect also genes not subject to genomic imprinting. We conclude that AS is caused by loss of function of a major gene that is imprinted but that there are also other genes that contribute to the phenotype when in hemizygous condition.