Endocrine Abstracts

The immune dysregulation, polyendocrinopathy and enteropathy, X-linked syndrome (IPEX), is a rare and devastating condition of male infants. Immune mediated diabetes and enteropathy occur before 6 months of age and other manifestations include hypothyroidism, recurrent infections and eczema. In 2001, IPEX was mapped to Xp11, an orthologous region to that for the murine model of T cell dysregulation, scurfy, and mutations in the forkhead transcription factor gene, FOXP3, were found in IPEX probands. We have used linkage analysis, mutational screening of the FOXP3 gene, HLA typing and analysis of X-chromosome inactivation to investigate 2 kindreds (21 subjects in total) with 4 male infants (3 now deceased) and 1 girl affected by IPEX. Eight X-chromosome microsatellite markers were genotyped in family members and linkage analysis was performed with X-GENEHUNTER. Direct DNA sequencing of the 11 exons, promoter and 3'UTR of the FOXP3 gene was performed on each proband. PCR of the HUMARA repeat polymorphism after digestion with the methylation sensitive enzyme HpaII was used to determine X-chromosome inactivation state. In one proband, a single base pair deletion was found at codon 76 in exon 2, leading to a frameshift, which predicted a truncated protein (108 residues vs 431 in WT). This change was confirmed using the restriction enzyme BfaI, and was not found in 217 control DNA samples. In the second family, the FOXP3 locus was excluded by recombination (multipoint LOD score -1.1) and mutational analysis of the gene was negative. The affected girl from this family had diabetes, hypothyroidism, pernicious anaemia and enteropathy, but was shown to have HLA DR2 and DR6 alleles and random X-chromosome inactivation in PBMC. Our analysis has elucidated the molecular basis of IPEX in one family and has, for the first time, provided evidence for an autosomal locus, suggesting genetic heterogeneity in this syndrome.