Familial tumoral calcinosis (FTC; OMIM 211900) is a severe autosomal recessive metabolic disorder that manifests with hyperphosphatemia and massive calcium deposits in the skin and subcutaneous tissues. Using linkage analysis, we mapped the gene underlying FTC to 2q24-q31. This region includes the gene GALNT3, which encodes a glycosyltransferase responsible for initiating mucin-type O-glycosylation. Sequence analysis of GALNT3 identified biallelic deleterious mutations in all individuals with FTC, suggesting that defective post-translational modification underlies the disease.We assessed 12 individuals with FTC from two large kindreds of Druze and African-American origin (Fig. 1a) that have been extensively described 1,2 . All affected individuals reported recurrent painful, calcified subcutaneous masses of up to 1 kg (Fig. 1b), often resulting in secondary infection and incapacitating mutilation. Three individuals developed deep periarticular tumors (Fig. 1b), and one succumbed to the disease. All affected individuals had hyperphosphatemia (family 1, 6.2-8.5 mg dl -1 ; family 2, 5.2-6.6 mg dl -1 ) but normal levels of calcium, parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D3.With informed consent of all participants, we obtained DNA samples and carried out a genome-wide scan using 362 microsatellite markers (Research Genetics) in family 1. Consanguinity in this kindred allowed us to apply homozygosity mapping to identify in all affected individuals a 15-Mb segment identical by descent, flanked by D2S142 and D2S2284/D2S2177 on 2q24-q31 (Fig. 1). We obtained a maximum multipoint lod score of 6.7 (HOMOZ 3 ). Multipoint linkage analysis in family 2 using seven markers in this critical region further reduced the interval to 3 Mb flanked by D2S111 and D2S1776 (Fig. 1) and yielded a maximum multipoint lod score of 3.4 (GeneHunter 4 ).Using Mapviewer, we identified 11 genes in the 3-Mb region associated with FTC. Of these, B3GALT1, SCN7A, SCN9A, SCN1A and STK39 have roles in neural or neuroendocrine tissues; the functions of TAIP-2, CMYA3, FLJ11457, LOC90643 and LASS6 are mostly unknown. The last positional candidate gene, GALNT3, encodes the UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase 3 (ppGaNTase-T3; ref. 5). ppGaNTase-T3 belongs to a large family of Golgi-associated biosynthetic enzymes that transfer GalNac from the sugar donor UDP-GalNac to serine and threonine residues and are thereby responsible for initiating O-glycan synthesis, a prevalent form of post-translational modification 6 . RT-PCR analysis showed strong expression of GALNT3 in the skin and kidneys, two tissues of functional relevance to the pathogenesis of FTC 1,2 (Fig. 2a). Using balanced primer pairs, we screened PCR amplicons of all ten coding exons and conserved splice sites of GALNT3 for pathogenic mutations in the genomic DNA of affected individuals (primer pairs and PCR conditions are available on request). Members of the Druze family carried a homozygous G→A transition at position 1524+1 (from the ATG ...

Neurocutaneous syndromes represent a vast, largely heterogeneous group of disorders characterized by neurological and dermatological manifestations, reflecting the common embryonic origin of epidermal and neural tissues. In the present report, we describe a novel neurocutaneous syndrome characterized by cerebral dysgenesis, neuropathy, ichthyosis, and keratoderma (CEDNIK syndrome). Using homozygosity mapping in two large families, we localized the disease gene to 22q11.2 and identified, in all patients, a 1-bp deletion in SNAP29, which codes for a SNARE protein involved in vesicle fusion. SNAP29 expression was decreased in the skin of the patients, resulting in abnormal maturation of lamellar granules and, as a consequence, in mislocation of epidermal lipids and proteases. These data underscore the importance of vesicle trafficking regulatory mechanisms for proper neuroectodermal differentiation.

In this article, we describe a novel autosomal recessive ichthyosis with hypotrichosis syndrome, characterized by congenital ichthyosis associated with abnormal hair. Using homozygosity mapping, we mapped the disease locus to 11q24.3-q25. We screened the ST14 gene, which encodes matriptase, since transplantation of skin from matriptase(-/-)-knockout mice onto adult athymic nude mice has been shown elsewhere to result in an ichthyosislike phenotype associated with almost complete absence of erupted pelage hairs. Mutation analysis revealed a missense mutation, G827R, in the highly conserved peptidase S1-S6 domain. Marked skin hyperkeratosis due to impaired degradation of the stratum corneum corneodesmosomes was observed in the affected individuals, which suggests that matriptase plays a significant role in epidermal desquamation.

The WNT-signaling pathway plays a major role during mammalian embryogenesis. We report a novel autosomal-recessive syndrome that consists of female to male sex reversal and renal, adrenal, and lung dysgenesis and is associated with additional developmental defects. Using a candidate-gene approach, we identified a disease-causing homozygous missense mutation in the human WNT4 gene. The mutation was found to result in markedly reduced WNT4 mRNA levels in vivo and in vitro and to downregulate WNT4-dependent inhibition of beta-catenin degradation. Taken together with previous observations in animal models, the present data attribute a pivotal role to WNT4 signaling during organogenesis in humans.

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