CHARACTERIZATION OF A NOVEL GENE, C21ORF2, AN HUMAN-CHROMOSOME 21Q22.3 AND ITS EXCLUSION AS THE APECED GENE BY MUTATION ANALYSIS

Exon trapping was performed from a partial cosmid, PAC, and P1 clone c ontig from human chromosome 21 between MX1 and 21qter to identify gene s that may be involved in the pathogenesis of Down syndrome or several of tile genetic diseases that map to chromosome 21q22.3. One 19-bp ex on showed ideality to three ESTs. The complete sequence of the EST clo nes. RT-PCR, and cDNA library screening were used to determine the ful l-length cDNA sequence of 2.2 kb with an open reading frame of 256-ami no-acids. The putative 256-amino-acid peptide has homology with a hypo thetical Caehorhabditis elegans protein of unknown fraction. Northern blot analysis of this gene, termed C21orf2 (chromosome 21 open reading frame 2), revealed two ubiquitously expressed mRNAs of 2,2 and 1.2 kb produced by use of alternative polyadenylation sites. Hybridization o f the EST clones to a cosmid contig in chromosome 21q22.3 mapped C21or f2 just distal to PFKL, a critical mapping region Eor several genetic diseases. Comparison to publicly available genomic sequence, and addit ional data, revealed that :he gene is split into seven exons over 10.5 kb, further refining the mapping position to only 1.2 kb distal to PF KL with the direction of transcription toward the centromere, The 5'UT R is contiguous with D21S400 and intron 2 contains a 52-bp VNTR polymo rphism, Given its mapping position, C21orf2 is a candidate for involve ment in disorders including autoimmune polyglandular disease type I (a lso called autoimmune polyendocrinopathy candidiasas ectodermal dystro phy or APECED) and the autosomal nonsyndromic deafness loci, DFNB8 and DFNB10. Mutation analysis using sequencing of RT-PCR and genomic DNA- derived PCR products, SSCP, and Southern and Northern blot analyses in APECED patients excluded C21orf2 as the gene for APECED. (C) 1998 Aca demic Press.