as a result of population-specific intronic sequences that predispose individuals to preferential deletion breakpoints.

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RB1 gene expression has been reported to be upregulated in colorectal carcinomas (CRC) at both the mRNA and protein levels when compared to normal colonic mucosa. However, allelic loss at the genomic level has been detected in CRC with widely differing frequencies ranging from 11.5% to 50%. To determine whether there is indeed a correlation between RB1 allelic imbalance (AI) and expression, a consecutive series of 55 CRC from Singapore patients were analysed by microsatellite analysis, real-time RT-PCR and immunohistochemistry. Microsatellite analysis using 3 RB1 intragenic microsatellite markers and 2 markers flanking RB1 detected AI in 32.7% (18/55) of the cases, in at least 1 locus. The highest AI frequency (22.9%) was observed at the microsatellite marker D13S137 (Cu13), which maps 5 cM distal to RB1. AI was present in both early and late Dukes stages. Real-time RT-PCR revealed that all 40 cases analysed expressed RB1 mRNA, with mRNA overexpression in 37.5% (15/40) and pRB protein expression in 88.2% (30/ 34) of cases. Notably, a statistically significant correlation was found between AI of RB1 and mRNA overexpression of RB1 (p < 0.001, Fishers exact test). These findings provide evidence that despite AI, RB1 expression is not abrogated. Thus, our data suggests that RB1 may play a role in colorectal tumorigenesis through functional regulation of the transcript and protein rather than through its tumour suppressor role by gene inactivation. ' 2006 Wiley-Liss, Inc.Key words: RB1; colorectal cancer; allelic imbalance; expressionThe retinoblastoma gene, RB1, is a well-known tumour suppressor gene that encodes a nucleoprotein (pRB) with a critical role in cell cycle regulation, proliferation, differentiation and apoptosis. Numerous studies have shown frequent loss of RB1 function and either low or no pRb expression in different tumour types, such as pituitary adenomas, 1 glioblastomas, 2,3 hepatocellular carcinomas 4 and sporadic retinoblastomas. 5 In contrast, RB1 gene expression has been reported to be upregulated in colorectal carcinomas (CRC) at both the mRNA and protein levels when compared to normal colonic mucosa.6-13 Consistent with this increased expression, RB1 transcripts and pRb are not truncated or absent in colorectal cancers, suggesting that Rb is functional in CRC. 12,14 At the genomic level, allelic loss detected by loss of heterozygosity (LOH) has also been reported in the RB1 region in CRC with widely differing frequencies ranging from 11.5% 15 to as high as 50% of cases studied.16,17 These differences in frequencies may be because LOH assays actually determine allelic imbalance which may indicate either loss or gain. Increased allelic copy number at polymorphic loci of RB1 has also been documented by densitometric comparisons of Southern blots in 32% of colorectal tumours, 18 as well as by fluorescence in situ hybridization analysis in 44% of colorectal adenomas. 19 The presence of RB1 allelic loss would suggest that its expression would be decreased, contradictory to previous expression stud...

Background/Aims: X-linked adrenal hypoplasia congenita (AHC) is typically associated with DAX-1 mutations and hypogonadotropic hypogonadism. However, atypical cases of X-linked AHC in association with central precocious puberty and even normal puberty have rarely been reported, although the mechanism of action remains unknown. Case Report: This is a case report of a boy with X-linked AHC associated with Duchenne muscular dystrophy, whose clinical presentation led to analysis of the DAX-1, glycerol kinase (GK1) and dystrophin genes, which were amplified by polymerase chain reaction, with Southern blot analysis of the AHC locus. Results: There was a non-contiguous deletion of the DAX-1 and GK1 genes, with deletion of the dystrophingene from exons 3 to 79. Conclusion: This is the first report of X-linked AHC, central precocious puberty in the absence of the DAX-1 gene. The fact that a ‘loss of function’ DAX-1 mutation can be associated with hypogonadotropic hypogonadism, precocious and normal puberty, suggests that DAX-1 is but one of several transcription factors which regulate puberty, and provides further evidence that other transcription factors may interact with DAX-1 and influence gonadal regulation in a complex, but hierarchical fashion.

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