NOTCH2 mutations in Alagille syndrome.

BACKGROUND: Alagille syndrome (ALGS) is a dominant, multisystem disorder caused by mutations in the Jagged1 (JAG1) ligand in 94% of patients, and in the NOTCH2 receptor in <1%. There are only two NOTCH2 families reported to date. This study hypothesised that additional NOTCH2 mutations would be present in patients with clinical features of ALGS without a JAG1 mutation. METHODS: The study screened a cohort of JAG1-negative individuals with clinical features suggestive or diagnostic of ALGS for NOTCH2 mutations. RESULTS: Eight individuals with novel NOTCH2 mutations (six missense, one splicing, and one non-sense mutation) were identified. Three of these patients met classic criteria for ALGS and five patients only had a subset of features. The mutations were distributed across the extracellular (N=5) and intracellular domains (N=3) of the protein. Functional analysis of four missense, one nonsense, and one splicing mutation demonstrated decreased Notch signalling of these proteins. Subjects with NOTCH2 mutations demonstrated highly variable expressivity of the affected systems, as with JAG1 individuals. Liver involvement was universal in NOTCH2 probands and they had a similar prevalence of ophthalmologic and renal anomalies to JAG1 patients. There was a trend towards less cardiac involvement in the NOTCH2 group (60% vs 100% in JAG1). NOTCH2 (+) probands exhibited a significantly decreased penetrance of vertebral abnormalities (10%) and facial features (20%) when compared to the JAG1 (+) cohort. CONCLUSIONS: This work confirms the importance of NOTCH2 as a second disease gene in ALGS and expands the repertoire of the NOTCH2 related disease phenotype.

Alagille syndrome in a Vietnamese cohort: mutation analysis and assessment of facial features.

Alagille syndrome (ALGS, OMIM #118450) is an autosomal dominant disorder that affects multiple organ systems including the liver, heart, eyes, vertebrae, and face. ALGS is caused by mutations in one of two genes in the Notch Signaling Pathway, Jagged1 (JAG1) or NOTCH2. In this study, analysis of 21 Vietnamese ALGS individuals led to the identification of 19 different mutations (18 JAG1 and 1 NOTCH2), 17 of which are novel, including the third reported NOTCH2 mutation in Alagille Syndrome. The spectrum of JAG1 mutations in the Vietnamese patients is similar to that previously reported, including nine frameshift, three missense, two splice site, one nonsense, two whole gene, and one partial gene deletion. The missense mutations are all likely to be disease causing, as two are loss of cysteines (C22R and C78G) and the third creates a cryptic splice site in exon 9 (G386R). No correlation between genotype and phenotype was observed. Assessment of clinical phenotype revealed that skeletal manifestations occur with a higher frequency than in previously reported Alagille cohorts. Facial features were difficult to assess and a Vietnamese pediatric gastroenterologist was only able to identify the facial phenotype in 61% of the cohort. To assess the agreement among North American dysmorphologists at detecting the presence of ALGS facial features in the Vietnamese patients, 37 clinical dysmorphologists evaluated a photographic panel of 20 Vietnamese children with and without ALGS. The dysmorphologists were unable to identify the individuals with ALGS in the majority of cases, suggesting that evaluation of facial features should not be used in the diagnosis of ALGS in this population. This is the first report of mutations and phenotypic spectrum of ALGS in a Vietnamese population.

Renal anomalies in Alagille syndrome: a disease-defining feature.

Alagille syndrome (ALGS) is an autosomal dominant condition, primarily caused by mutations in JAGGED1. ALGS is defined by cholestatic liver disease, cardiac disease and involvement of the face, skeleton, and eyes with variable expression of these features. Renal involvement has been reported though not formally described. The objective of this study was to systematically characterize the renal involvement in ALGS. We performed a retrospective review of 466 JAGGED1 mutation-positive ALGS patients. Charts were reviewed for serum biochemistries, renal ultrasounds or other imaging, urinalysis, and clinical reports from pediatric nephrologists. The clinical data were reviewed by two pediatric hepatologists and a pediatric nephrologist. Of 466 charts reviewed we found 187 yielded evaluable renal information. Of these, 73/187 were shown to have renal involvement, representing 39% of the study cohort. Renal dysplasia was the most common anomaly seen. Genotype analysis of the JAGGED1 mutations in the patients with and without renal involvement did not reveal an association with mutation type. From the study we concluded that renal involvement has a prevalence of 39% in ALGS in our evaluable patients. Renal dysplasia is the most common renal anomaly. This finding correlates with the known role of the Notch pathway in glomerular development. Since renal disease of the type seen in ALGS can impair growth and impact liver transplantation, there is a clear need for a prospective study of renal involvement in ALGS and the development of guidelines for evaluation and management. These data also suggest that renal involvement be considered the sixth defining criterion for ALGS.

Jagged1 (JAG1) mutations in patients with tetralogy of Fallot or pulmonic stenosis.

Mutations in the Notch pathway ligand Jagged1 (JAG1) cause Alagille syndrome (AGS), as well as cardiac defects in seemingly nonsyndromic individuals. To estimate the frequency of JAG1 mutations in cases with right-sided cardiac defects not otherwise diagnosed with AGS, we screened 94 cases with tetralogy of Fallot (TOF) and 50 with pulmonic stenosis/peripheral pulmonary stenosis (PS/PPS) or pulmonary valve atresia with intact ventricular septum (PA) for mutations. Sequence changes were identified in three TOF and three PS/PPS/PA patients, that were not present in 100 controls. We identified one frameshift and two missense mutations in the TOF cases, and one frameshift and two missense mutations in cases with PS/PPS/PA. The four missense mutations were assayed for their effect on protein localization, posttranslational modification, and ability to activate Notch signaling. The missense mutants displayed heterogeneous behavior in these assays, some with complete haploinsufficiency, suggesting that there are additional modifiers leading to organ specific features. We identified functionally significant mutations in 2% (2/94) of TOF patients and 4% (2/50) of PS/PPS/PA patients. Patients with right-sided cardiac defects should be carefully screened for features of AGS or a family history of cardiac defects that might suggest the presence of a JAG1 mutation.

Genomic alterations in biliary atresia suggest region of potential disease susceptibility in 2q37.3.

Biliary atresia (BA) is a progressive, idiopathic obliteration of the extrahepatic biliary system occurring exclusively in the neonatal period. It is the most common disease leading to liver transplantation in children. The etiology of BA is unknown, although infectious, immune and genetic causes have been suggested. Although the recurrence of BA in families is not common, there are more than 30 multiplex families reported and an underlying genetic susceptibility has been hypothesized. We screened a cohort of 35 BA patients for genomic alterations that might confer susceptibility to BA. DNA was genotyped on the Illumina Human Hap 550 Beadchip platform, which analyzes over 550,000 single nucleotide polymorphisms (SNPs) for genomic deletions and duplications. Areas of increased and decreased copy number were compared to those found in control populations. To identify regions that could serve as susceptibility factors for BA, we searched for regions that were found in BA patients, but not in controls. We identified two unrelated BA patients with overlapping heterozygous deletions of 2q37.3. Patient 1 had a 1.76 Mb (280 SNP), heterozygous deletion containing 30 genes. Patient 2 had a 5.87 Mb (1,346 SNP) heterozygous deletion containing 55 genes. The overlapping 1.76 Mb deletion on chromosome 2q37.3 from 240,936,900 to 242,692,820 constitutes the critical region and the genes within this region could be candidates for susceptibility to BA.

Full gene HLA class I sequences of 79 novel and 519 mostly uncommon alleles from a large United States registry population.

HLA class I assignments were obtained at single genotype, G-level resolution from 98 855 volunteers for an unrelated donor registry in the United States. In spite of the diverse ancestry of the volunteers, over 99% of the assignments at each locus are common. Within this population, 52 novel alleles differing in exons 2 and 3 are identified and characterized. Previously reported alleles with incomplete sequences in the IPD-IMGT/HLA database (n = 519) were selected for full gene sequencing and, from this sampling, another 27 novel alleles are described.

Spectrum of JAG1 gene mutations in Polish patients with Alagille syndrome.

Alagille syndrome (ALGS) is an autosomal dominant disorder characterized by developmental abnormalities in several organs including the liver, heart, eyes, vertebrae, kidneys, and face. The majority (90-94%) of ALGS cases are caused by mutations in the JAG1 (JAGGED1) gene, and in a small percent of patients (∼1%) mutations in the NOTCH2 gene have been described. Both genes are involved in the Notch signaling pathway. To date, over 440 different JAG1 gene mutations and ten NOTCH2 mutations have been identified in ALGS patients. The present study was conducted on a group of 35 Polish ALGS patients and revealed JAG1 gene mutations in 26 of them. Twenty-three different mutations were detected including 13 novel point mutations and six large deletions affecting the JAG1 gene. Review of all mutations identified to date in individuals from Poland allowed us to propose an effective diagnostic strategy based on the mutations identified in the reported patients of Polish descent. However, the distribution of mutations seen in this cohort was not substantively different than the mutation distribution in other reported populations.

Differential methylation persists at the mouse Rasgrf1 DMR in tissues displaying monoallelic and biallelic expression.

A subset of mammalian genes exhibits genomic imprinting, whereby one parental allele is preferentially expressed. Differential DNA methylation at imprinted loci serves both to mark the parental origin of the alleles and to regulate their expression. In mouse, the imprinted gene Rasgrf1 is associated with a paternally methylated imprinting control region which functions as an enhancer blocker in its unmethylated state. Because Rasgrf1 is imprinted in a tissue-specific manner, we investigated the methylation pattern in monoallelic and biallelic tissues to determine if methylation of this region is required for both imprinted and non-imprinted expression. Our analysis indicates that DNA methylation is restricted to the paternal allele in both monoallelic and biallelic tissues of somatic and extraembryonic lineages. Therefore, methylation serves to mark the paternal Rasgrf1 allele throughout development, but additional factors are required for appropriate tissue-specific regulation of expression at this locus.