Search

Background: The 11p15 region contains two clusters of imprinted genes. Opposite genetic and epigenetic anomalies of this region result in two distinct growth disturbance syndromes: Beckwith-Wiedemann (BWS) and Silver-Russell syndromes (SRS). Cytogenetic rearrangements within this region represent less than 3% of SRS and BWS cases. Among these, 11p15 duplications were infrequently reported and interpretation of their pathogenic effects is complex. Objectives: To report cytogenetic and methylation analyses in a cohort of patients with SRS/BWS carrying 11p15 duplications and establish genotype/phenotype correlations. Methods: From a cohort of patients with SRS/BWS with an abnormal methylation profile (using ASMM-RT Q-PCR), we used SNP-arrays to identify and map the 11p15 duplications. We report 19 new patients with SRS (n=9) and BWS (n=10) carrying de novo or familial 11p15 duplications, which completely or partially span either both telomeric and centromeric domains or only one domain. Results: Large duplications involving one complete domain or both domains are associated with either SRS or BWS, depending on the parental origin of the duplication. Genotype-phenotype correlation studies of partial duplications within the telomeric domain demonstrate the prominent role of IGF2, rather than H19, in the control of growth. Furthermore, it highlights the role of CDKN1C within the centromeric domain and suggests that the expected overexpression of KCNQ1OT1 from the paternal allele (in partial paternal duplications, excluding CDKN1C) does not affect the expression of CDKN1C. Conclusions: The phenotype associated with 11p15 duplications depends on the size, genetic content, parental inheritance and imprinting status. Identification of these rare duplications is crucial for genetic counselling. [ABSTRACT FROM AUTHOR]

Objectives: Silver-Russell syndrome (SRS) is an imprinted disorder characterised by intrauterine growth retardation, relative macrocephaly, failure to thrive, typical facial phenotype and frequent body asymmetry. Feeding difficulties are frequently noted, but no study described evolution of gastrointestinal signs during infancy and their management in SRS. The aim of this study was to describe these abnormalities in a large cohort of children with SRS. Design: We included 75 patients (median age 24.3 months (5.1-135.2)) in the study. We retrospectively analysed nutritional status before growth hormone therapy, the frequency of gastrointestinal signs, such as gastroesophageal reflux (GER), vomiting, constipation and feeding difficulties, and nutritional management. Results: Maternal uniparental disomy for chromosome 7 was found in 10 patients and 11p15 hypomethylation in 65 patients. Malnutrition (defined as a weight/ expected weight for height ratio <80%) was detected in 70% of the children. Gastrointestinal signs were found in 77%, including severe vomiting before the age of 1 year in 50% of cases, persistent vomiting from the age of 1 year in 29% of cases and constipation in 20% of cases. Severe GER was diagnosed in 55% of children by 24 h oesophageal pH-metry. Feeding difficulties were described in 65% of cases, with indications for dietary enrichment in 49%. Enteral nutrition by gastrostomy was indicated in 22% of cases. Conclusions: Digestive signs (GER, constipation) and malnutrition are frequent in children with SRS. The systematic exploration and management of these signs are crucial to improve the nutritional status of these children before initiating growth hormone therapy. [ABSTRACT FROM AUTHOR]

Background The structural organisation of the human IGF2/ICR1/H19 11p15 domain is very complex, and the mechanisms underlying its regulation are poorly understood. The Imprinted Center Region 1 (ICR1) contains seven binding sites for the zinc-finger protein CTCF (CBS: CTCF Binding Sites); three additional differentially methylated regions (DMR) are located at the H19 promoter (H19DMR) and two in the IGF2 gene (DMR0 and DMR2), respectively. Loss of imprinting at the IGF2/ICR1/H19 domain results in two growth disorders with opposite phenotypes: Beckwith- Wiedemann syndrome and Russell Silver syndrome (RSS). Despite the IGF2/ICR1/H19 locus being widely studied, the extent of hypomethylation across the domain remains not yet addressed in patients with RSS. Methods We assessed a detailed investigation of the methylation status of the 11p15 ICR1 CBS1-7, IGF2DMR0 and H19DMR (H19 promoter) in a population of controls (n=50) and RSS carrying (n=104) or not (n=65) carrying a hypomethylation at the 11p15 ICR1 region. Results The methylation indexes (MI) were balanced at all regions in the control population and patients with RSS without any as yet identified molecular anomaly. Interestingly, patients with RSS with ICR1 hypomethylation showed uneven profiles of methylation among the CBSs and DMRs. Furthermore, normal MIs at CBS1 and CBS7 were identified in 9% of patients. Conclusions The hypomethylation does not spread equally throughout the IGF2/ICR1/H19 locus, and some loci could have normal MI, which may lead to underdiagnosis of patients with RSS with ICR1 hypomethylation. The uneven pattern of methylation suggests that some CBSs may play different roles in the tridimensional chromosomal looping regulation of this locus. [ABSTRACT FROM AUTHOR]

Background Disruption of 11p15 imprinting results in two fetal growth disorders with opposite phenotypes: the Beckwith-Wiedemann (BWS; MIM 130650) and the Silver-Russell (SRS; MIM 180860) syndromes. DNA methylation defects account for 60% of BWS and SRS cases and, in most cases, occur without any identified mutation in a cis-acting regulatory sequence or a transacting factor. Methods We investigated whether 11p15 cis-acting sequence variants account for primary DNA methylation defects in patients with SRS and BWS with loss of DNA methylation at ICR1 and ICR2, respectively. Results We identified a 4.5 kb haplotype that, upon maternal transmission, is associated with a risk of ICR2 loss of DNA methylation in patients with BWS. This novel region is located within the second intron of the KCNQ1 gene, 170 kb upstream of the ICR2 imprinting centre and encompasses two CTCF binding sites. We showed that, within the 4.5 kb region, two SNPs (rs11823023 and rs179436) affect CTCF occupancy at DNA motifs flanking the CTCF 20 bp core motif. Conclusions This study shows that genetic variants confer a risk of DNA methylation defect with a parentof- origin effect and highlights the crucial role of CTCF for the regulation of genomic imprinting of the CDKN1C/ KCNQ1 domain. [ABSTRACT FROM AUTHOR]

Background Apparently balanced chromosomal rearrangements (ABCR) are associated with an abnormal phenotype in 6% of cases. This may be due to cryptic genomic imbalances or to the disruption of genes at the breakpoint. However, breakpoint cloning using conventional methods (ie, fluorescent in situ hybridisation (FISH), Southern blot) is often laborious and time consuming. In this work, we used next generation sequencing (NGS) to locate breakpoints at the molecular level in four patients with multiple congenital abnormalities and/or intellectual deficiency (MCA/ID) who were carrying ABCR (one translocation, one complex chromosomal rearrangement and two inversions), which corresponded to nine breakpoints. Methods Genomic imbalance was previously excluded by array comparative genomic hybridisation (CGH) in all four patients. Whole genome paired-end protocol was used to identify breakpoints. The results were verified by FISH and by PCR with Sanger sequencing. Results We were able to map all nine breakpoints. NGS revealed an additional breakpoint due to a cryptic inversion at a breakpoint junction in one patient. Nine of 10 breakpoints occurred in repetitive elements and five genes were disrupted in their intronic sequence (TCF4, SHANK2, PPFIA1, RAB19, KCNQ1). Conclusions NGS is a powerful tool allowing rapid breakpoint cloning of ABCR at the molecular level. We showed that in three out of four patients, gene disruption could account for the phenotype, allowing adapted genetic counselling and stopping unnecessary investigations. We propose that patients carrying ABCR with an abnormal phenotype should be explored systematically by NGS once a genomic imbalance has been excluded by array CGH. [ABSTRACT FROM AUTHOR]