Mal de Meleda (MDM) is a rare autosomal recessive skin disorder, characterized by transgressive palmoplantar keratoderma (PPK), keratotic skin lesions, perioral erythema, brachydactyly and nail abnormalities. We report the refinement of our previously described interval of MDM on chromosome 8qter, and the identification of mutations in affected individuals in the ARS (component B) gene, encoding a protein named SLURP-1, for secreted Ly-6/uPAR related protein 1. This protein is a member of the Ly-6/uPAR superfamily, in which most members have been localized in a cluster on chromosome 8q24.3. The amino acid composition of SLURP-1 is homologous to that of toxins such as frog cytotoxin and snake venom neurotoxins and cardiotoxins. Three different homozygous mutations (a deletion, a nonsense and a splice site mutation) were detected in 19 families of Algerian and Croatian origin, suggesting founder effects. Moreover, one of the common haplotypes presenting the same mutation was shared by families from both populations. Secreted and receptor proteins of the Ly-6/uPAR superfamily have been implicated in transmembrane signal transduction, cell activation and cell adhesion. This is the first instance of a secreted protein being involved in a PPK.

To assess the role of insulin receptor, insulin receptor substrate (IRS)-1, and IRS-2 genes in insulin resistance, we explored the genomic DNA in women with polycystic ovary syndrome (PCOS) and a variable degree (mean ؎ SE) of insulin resistance (homeostasis model assessment index for insulin resistance [HOMA IR ] 3.2 ؎ 0.6, n ‫؍‬ 53; control subjects 1.56 ؎ 0.34, n ‫؍‬ 102) using direct sequencing. Whereas no novel mutations were found in these genes, gene-dosage effects were found on fasting insulin for the Gly972Arg IRS-1 variant and on 2-h plasma glucose for the Gly1057Asp IRS-2 variant. The Gly972Arg IRS-1 variant was more prevalent in insulin-resistant patients compared with non-insulinresistant individuals or control subjects (39.3 vs. 4.0 and 16.6%, P < 0.0031, respectively). A multivariate model that included BMI as a variable revealed significant effects of the Gly1057Asp IRS-2 variant on insulin resistance (P < 0.016, odds ratio [OR] 7.2, 95% CI 1.29 -43.3). HOMA IR was higher in carriers of both IRS variants than in those with IRS-2 mutations only or those with wild-type variants (6.2 ؎ 2.3, 2.8 ؎ 0.5, and 1.8 ؎ 0.2, respectively; P < 0.01), and it was significantly associated with this genotype (P < 0.0085, OR 1.7, 95% CI 1.09 -2.99). We conclude that polymorphic alleles of both IRS-1 and IRS-2, alone or in combination, may have a functional impact on the insulin-resistant component of PCOS.

Erythrokeratodermia variabilis (EKV) is an autosomal dominant keratinization disorder characterized by migratory erythematous lesions and fixed keratotic plaques. All families with EKV show mapping to chromosome 1p34-p35, and mutations in the gene for connexin 31 (Cx31) have been reported in some but not all families. We studied eight affected and three healthy subjects in an Israeli family, of Kurdish origin, with EKV. After having mapped the disorder to chromosome 1p34-p35, we found no mutations in the genes for Cx31, Cx31.1, and Cx37. Further investigation revealed a heterozygous TrC transition leading to the missense mutation (F137L) in the human gene for Cx30.3 that colocalizes on chromosome 1p34-p35. This nucleotide change cosegregated with the disease and was not found in 200 alleles from normal individuals. This mutation concerns a highly conserved phenylalanine, in the third transmembrane region of the Cx30.3 molecule, known to be implicated in the wall formation of the gap-junction pore. Our results show that mutations in the gene for Cx30.3 can be causally involved in EKV and point to genetic heterogeneity of this disorder. Furthermore, we suggest that our family presents a new type of EKV because of the hitherto unreported association with erythema gyratum repens.Connexins (denoted by the prefix "Cx") are a family of polypeptides that form the subunits of the gap-junction channels. Members of the connexin family are characterized by four hydrophobic transmembrane domains (M1-M4) that are linked by one cytoplasmic and two extracellular (E1 and E2) loops. The N and C termini are located on the cytoplasmic membrane face. Extracellular-loop and transmembrane domains display the highest homology between the connexin family members, whereas the cytoplasmic loop and the C-terminal region are highly variable. Six connexin polypeptides assemble into a connexon, a hemichannel that interacts with its counterpart on adjacent cells to form a complete intercellular channel, thereby connecting the cytoplasm of neighboring cells (Yeager and Nicholson 1996). Gap junctions are composed of numerous aggregated con-

Erythrokeratodermia variabilis (EKV) is an autosomal dominant keratinization disorder characterized by migratory erythematous lesions and fixed keratotic plaques. All families with EKV show mapping to chromosome 1p34-p35, and mutations in the gene for connexin 31 (Cx31) have been reported in some but not all families. We studied eight affected and three healthy subjects in an Israeli family, of Kurdish origin, with EKV. After having mapped the disorder to chromosome 1p34-p35, we found no mutations in the genes for Cx31, Cx31.1, and Cx37. Further investigation revealed a heterozygous T-->C transition leading to the missense mutation (F137L) in the human gene for Cx30.3 that colocalizes on chromosome 1p34-p35. This nucleotide change cosegregated with the disease and was not found in 200 alleles from normal individuals. This mutation concerns a highly conserved phenylalanine, in the third transmembrane region of the Cx30.3 molecule, known to be implicated in the wall formation of the gap-junction pore. Our results show that mutations in the gene for Cx30.3 can be causally involved in EKV and point to genetic heterogeneity of this disorder. Furthermore, we suggest that our family presents a new type of EKV because of the hitherto unreported association with erythema gyratum repens.

Connexins are homologous four-transmembrane-domain proteins and major components of gap junctions. We recently identified mutations in either GJB3 or GJB4 genes, encoding respectively connexin 31 (Cx31) or 30.3 (Cx30.3), as causally involved in erythrokeratodermia variabilis (EKV), a mostly autosomal dominant disorder of keratinization. Despite slight differences, phenotypes of EKV Mendes Da Costa (Cx31) and EKV Cram-Mevorah (Cx30.3) show major clinical overlap and both Cx30.3 and Cx31 are expressed in the upper epidermal layers. These similarities suggested to us that Cx30.3 and Cx31 may interact at a molecular level. Indeed, expression of wild-type Cx30.3 in HeLa cell resulted only in minor amounts of protein addressed to the plasma membrane. Mutant Cx30.3 was hardly detectable and disturbed intercellular coupling. In sharp contrast, co-expression of both wild-type proteins led to a gigantic increase of stabilized heteromeric gap junctions. Furthermore, co-expressed wild-type Cx30.3 and Cx31 coprecipitate, which demonstrates a physical interaction. Inhibitor experiments revealed that this interaction begins in the endoplasmic reticulum. These results not only provide new insights into epidermal connexin synthesis and polymerization, but also allow a novel molecular explanation for the similarity of EKV phenotypes.