Introduction: Heterozygous mutations in JAGGED1 (JAG1), encoding a ligand for Notch receptors, have been identified in 70 % of patients with Alagille syndrome (AGS), using PCR-SSCP (single strand conformation polymorphism). These mutations are located in the extracellular and transmembrane domains of the protein and 70 % of them lead to a premature termination codon (PTC). However, only few studies of the modified mRNAs have been performed. Methods: and aims: To improve the molecular diagnosis of AGS, we have performed RT-PCR analyses and sequencing from mRNAs of lymphoblastoid cell lines derived from 11 patients with no mutations identified by PCR-SSCP. In addition, we have studied the mutant transcript levels in 21 cell lines from AGS patients with already identified mutations, and from the tissues of a 23-week-old fetus with AGS. Results: 1/ in 3 of the patients without previously identified mutations, JAG1 mutations were found by RT-PCR analysis, 2/ in the 8 other patients, no mutation was found in the cDNA of JAG1, supporting the hypothesis of genetic heterogeneity, 3/ mutant transcripts were recovered from lymphoblastoid cells of all patients with missense mutations (5) or in-phase deletions (2), and from all but one of the 16 with PTC, 4/ mutant transcripts were present in tissues of the 23 week-old fetus, albeit in different relative amounts; this could originate from tissue specificity of nonsense mediated mRNA decay. Conclusion: We found that some JAGGED1 mutations not detected by PCR-SSCP were identified by RT-PCR analysis on lymphoblastoid cells with no treatment against the nonsense mediated mRNA decay, but that some AGS patients have no mutation in the cDNA of JAGGED1 supporting the hypothesis of genetic heterogeneity. Mutant transcripts were recovered whatever the mutations, even with PTC, suggesting that both haploinsufficiency and a dominant negative effect could be involved in molecular mechanisms of AGS.
Other names: Alagille-Watson syndrome (AWS); arteriohepatic dysplasia (AHD); cholestasis with peripheral pulmonary stenosis; hepatic ductular paucity, syndromatic Note: syndrome associating 5 major features (complete syndrome): paucity of interlobular bile ducts, pulmonary artery stenosis, butterfly-like vertebrae, posterior embryotoxon and a peculiar face. Only the 2 first ones are symptomatic. Incomplete syndrome is very frequent. Other features have been described involving kidney, cardiac and vascular anomalies including tetralogy of Fallot, ear, pancreas, intestine etc. Inheritance: autosomal dominant with a highly variable expressivity and nearly complete penetrance; frequency is about 1/70,000-100,000 live newborns; 60-70% are sporadic cases.
We have investigated that organization and the distribution of a family of interspersed DNA repeats in the mouse genome. The repeats are at least 5600 base pairs (bp) in size and contain two contiguous BamHI endonuclease fragments, 4000 and 540 bp in size, the larger of which includes a 1350-bp EcoRI fragment studied by previous authors. The repeats are polymorphic in their restriction maps, and represent the major family of interspersed repeats in the mouse genome. The repeats are present almost exclusively in the two light major components of mouse DNA, and the base composition of their large BamHI fragments matches that of those components. The genomic distribution of the repeats is different from that of structural genes, which are present not only in the two light components but also in the two heavy components of mouse DNA. This distribution indicates that the repeats are not involved, at least in any simple way, in the regulation of gene expression.
