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A gene, ATM, that is mutated in the autosomal recessive disorder ataxia telangiectasia (AT) was identified by positional cloning on chromosome 11q22-23. AT is characterized by cerebellar degeneration, immunodeficiency, chromosomal instability, cancer predisposition, radiation sensitivity, and cell cycle abnormalities. The disease is genetically heterogeneous, with four complementation groups that have been suspected to represent different genes. ATM, which has a transcript of 12 kilobases, was found to be mutated in AT patients from all complementation groups, indicating that it is probably the sole gene responsible for this disorder. A partial ATM complementary DNA clone of 5.9 kilobases encoded a putative protein that is similar to several yeast and mammalian phosphatidylinositol-3' kinases that are involved in mitogenic signal transduction, meiotic recombination, and cell cycle control. The discovery of ATM should enhance understanding of AT and related syndromes and may allow the identification of AT heterozygotes, who are at increased risk of cancer.

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Transcription factor paralogs may share a common role in staged or overlapping expression in specific tissues, as in the Hox family. In other cases, family members have distinct roles in a range of embryologic, differentiation or response pathways (as in the Tbx and Pax families). For the interferon regulatory factor (IRF) family of transcription factors, mice deficient in Irf1, Irf2, Irf3, Irf4, Irf5, Irf7, Irf8 or Irf9 have defects in the immune response but show no embryologic abnormalities. Mice deficient for Irf6 have not been reported, but in humans, mutations in IRF6 cause two mendelian orofacial clefting syndromes, and genetic variation in IRF6 confers risk for isolated cleft lip and palate. Here we report that mice deficient for Irf6 have abnormal skin, limb and craniofacial development. Histological and gene expression analyses indicate that the primary defect is in keratinocyte differentiation and proliferation. This study describes a new role for an IRF family member in epidermal development.

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PAPA syndrome (pyogenic sterile arthritis, pyoderma gangrenosum, and acne, OMIM #604416) and familial recurrent arthritis (FRA) are rare inherited disorders of early onset, primarily affecting skin and joint tissues. Recurring inflammatory episodes lead to accumulation of sterile, pyogenic, neutrophil-rich material within the affected joints, ultimately resulting in significant destruction. We recently localized the genes for PAPA syndrome and FRA to chromosome 15q and suggested that they are the same disorder. We have now established this by the identification of co-segregating disease-causing mutations in the CD2-binding protein 1 (CD2BP1; GenBank accession no XM 044569) gene in the two reported families with this disorder. E250Q or A230T amino acid substitutions occur within a domain highly homologous to yeast cleavage furrow-associated protein CDC15. CD2BP1 and its murine ortholog, proline-serine-threonine phosphatase interacting protein (PSTPIP1), are adaptor proteins known to interact with PEST-type protein tyrosine phosphatases (PTP). Yeast two-hybrid assays demonstrate severely reduced binding between PTP PEST and both the E250Q and A230T mutant proteins. Previous evidence supports the integral role of CD2BP1 and its interacting proteins in actin reorganization during cytoskeletal-mediated events. We hypothesize that the disease-causing mutations that we have identified compromise physiologic signaling necessary for the maintenance of proper inflammatory response. Accordingly we suggest classification of PAPA syndrome as an autoinflammatory disease. This CD2BP1-mediated biochemical pathway(s) may function in common inflammatory disorders with apparent etiological overlap, such as rheumatoid arthritis and inflammatory bowel disease.

Vesicular transport to and from the lysosome and late endosome is defective in patients with Chediak-Higashi syndrome (CHS) and in mutant beige (bg) mice. CHS and bg cells have giant, perinuclear vesicles with characteristics of late endosomes and lysosomes that arise from dysregulated homotypic fusion. CHS and bg lysosomes also exhibit compartmental missorting of proteins, such as elastase, glucuronidase and cathepsin G. Lyst, a candidate gene for bg, was identified by direct complementary DNA selection from a yeast artificial chromosome (YAC) clone containing a 650-kilobase segment of the bg-critical region on mouse chromosome 13. Lyst is disrupted by a 5-kilobase deletion in bg mice, and Lyst messenger RNA is markedly reduced in bg homozygotes. The homologous human gene, LYST, is highly conserved with mouse Lyst, and contains a frame-shift mutation at nucleotides 117-118 of the coding domain in a CHS patient. Thus bg mice and human CHS patients have homologous disorders associated with Lyst mutations. Lyst encodes a protein with a carboxy-terminal prenylation motif and multiple potential phosphorylation sites. Lyst protein is predicted to form extended helical domains, and has a region of sequence similar to stathmin, a coiled-coil phosphoprotein thought to act as a relay integrating cellular signal response coupling.