Human GFRA1: cloning, mapping, genomic structure, and evaluation as a candidate gene for Hirschsprung disease susceptibility.
Angrist M. Jing S. Bolk S. Bentley K. Nallasamy S. Halushka M. Fox GM. Chakravarti A.
Department of Genetics, Case Western Reserve University, Cleveland, Ohio 44106-4955, USA.
Congenital aganglionic megacolon, commonly known as Hirschsprung disease (HSCR), is the most frequent cause of congenital bowel obstruction. Germline mutations in the RET receptor tyrosine kinase have been shown to cause HSCR. Knockout mice for RET and for its ligand, glial cell line-derived neurotrophic factor (GDNF), exhibit both complete intestinal aganglionosis and renal defects. Recently, GDNF and GFRA1 (GDNF family receptor, also known as GDNFR-alpha), its GPI-linked coreceptor, were demonstrated to be components of a functional ligand for RET. Moreover, GDNF has been implicated in rare cases of HSCR. We have mapped GFRA1 to human chromosome 10q25, isolated human and mouse genomic clones, determined the gene's intron-exon boundaries, isolated a highly polymorphic microsatellite marker adjacent to exon 7, and scanned for GFRA1 mutations in a large panel of HSCR patients. No evidence of linkage was detected in HSCR kindreds, and no sequence variants were found to be in significant excess in patients. These data suggest that GFRA1'S role in enteric neurogenesis in humans remains to be elucidated and that RET signaling in the gut may take place via alternate pathways, such as the recently described GDNF-related molecule neurturin and its GFRA1-like coreceptor, GFRA2.
Cystic fibrosis Delta F508 heterozygotes, smoking, and reproduction: studies of 9141 individuals from a general population sample.
Dahl M. Tybjaerg-Hansen A. Wittrup HH. Lange P. Nordestgaard BG.
Department of Clinical Biochemistry, Herlev University Hospital, Herlev, DK-2730, Denmark.
Cystic fibrosis is the most common fatal autosomal recessive disease affecting Caucasian populations. It remains a puzzle how this disease is maintained at such a remarkably high incidence, however, it could be due to a reproductive advantage in cystic fibrosis heterozygotes. We tested this hypothesis. An adult Danish general population sample of 9141 individuals was screened for cystic fibrosis DeltaF508 heterozygotes; 250 carriers of this mutation were identified (2.7%). In the total sample DeltaF508 heterozygotes did not have more children than noncarriers; however, smoking interacted with genotype in predicting number of children (ANOVA: P < 0.001). Among nonsmokers, heterozygotes had more children than noncarriers (Wilcoxon: P = 0.03). Among smokers, the opposite was found: heterozygotes had fewer children than noncarriers (Wilcoxon: P = 0. 001). These findings remained significant after allowing for gender and the potential confounders of age, income, and education. Finally, after allowing for these covariates, number of children in DeltaF508 heterozygotes decreased with increasing extent of smoking (trend test: P = 0.003), while the opposite was true for noncarriers (trend test: P < 0.001). In conclusion, overall these results do not support a reproductive advantage for cystic fibrosis DeltaF508 heterozygotes. However, the data cannot totally exclude the possibility that nonsmoking DeltaF508 heterozygotes experience a reproductive advantage while smoking DeltaF508 heterozygotes experience the opposite, a reproductive disadvantage. Accordingly, the data suggest a previously undocumented role of smoking on fecundity among cystic fibrosis heterozygotes.