DNA methylation studies on imprinted loci in a male monozygotic twin pair discordant for Beckwith-Wiedemann syndrome

Tierling S, Souren NY, Reither S, Zang KD, Meng-Hentschel J, Leitner D, Oehl-Jaschkowitz B, Walter J. DNA methylation studies on imprinted loci in a male monozygotic twin pair discordant for Beckwith-Wiedemann syndrome. Beckwith-Wiedemann syndrome (BWS) is one of the most prevalent congenital disorders predominantly caused by epigenetic alterations. Here we present an extensive case study of a monozygotic monochorionic male twin pair discordant for BWS. Our analysis allows to correlate BWS symptoms, like a protruding tongue, indented ears and transient neonatal hypoglycaemia, to an abnormal methylation at the KvDMR1. DNAs extracted from peripheral blood, skin fibroblasts, saliva and buccal swab of both twins, their sister and parents were analysed at 11 differentially methylated regions (DMRs) including all four relevant DMRs of the BWS region. The KvDMR1 was exclusively found to be hypomethylated in all cell types of the affected BWS twin, while the unaffected twin and the relatives showed normal methylation in fibroblasts, buccal swab and saliva DNA. Interestingly, the twins share a common blood-specific hypomethylation phenotype most probably caused by a feto-fetal transfusion between both twins. Because microsatellite analysis furthermore revealed a normal biparental karyotype for chromosome 11, our results point to an exclusive correlation of the observed BWS symptoms to locally restricted epimutations at the KvDMR1 of the maternal chromosome

Anthropometry, carbohydrate and lipid metabolism in the East Flanders Prospective Twin Survey: linkage of candidate genes using two sib-pair based variance components analyses

Insulin resistance and obesity are underlying causes of type 2 diabetes and therefore much interest is focused on the potential genes involved. A series of anthropometric and metabolic characteristic were measured in 240 MZ and 112 DZ twin pairs recruited from the East Flanders Prospective Twin Survey. Microsatellite markers located close to ABCC8, ADIPOQ, GCK, IGF1, IGFBP1, INSR, LEP, LEPR, PPARgamma and the RETN gene were genotyped. Univariate single point variance components linkage analyses were performed using two methods: (1) the standard method, only comprising the phenotypic and genotypic data of the DZ twin pairs and (2) the extended method, also incorporating the phenotypic data of the MZ twin pairs. Suggestive linkages (LOD > 1) were observed between the ABCC8 marker and waist-to-hip ratio and HDL-cholesterol levels. Both markers flanking ADIPOQ showed suggestive linkage with triglycerides levels, the upstream marker also with body mass and HDL-cholesterol levels. The IGFBP1 marker showed suggestive linkage with fat mass, fasting insulin and leptin levels and the LEP marker showed suggestive linkage with birth weight. This study suggests that DNA variants in ABCC8, ADIPOQ, IGFBP1 and LEP gene region may predispose to type 2 diabetes. In addition, the two methods used to perform linkage analyses yielded similar results. This was however not the case for birth weight where chorionicity seems to be an important confounder

Assisted reproductive technologies do not enhance the variability of DNA methylation imprints in human

BACKGROUND Assisted reproductive technologies (ART) such as in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI) are believed to destabilise genomic imprints. An increased frequency of Beckwith-Wiedemann syndrome in children born after ART has been reported. Other, mostly epidemiological, studies argue against this finding. OBJECTIVE To examine the effect of ART on the stability of DNA methylation imprints, DNA was extracted from maternal peripheral blood (MPB), umbilical cord blood (UCB) and amnion/chorion tissue (ACT) of 185 phenotypically normal children (77 ICSI, 35 IVF, and 73 spontaneous conceptions). Using bisulfite based technologies 10 differentially methylated regions (DMRs) were analysed, including KvDMR1, H19, SNRPN, MEST, GRB10, DLK1/MEG3 IG-DMR, GNAS NESP55, GNAS NESPas, GNAS XL-alpha-s and GNAS Exon1A. RESULTS Methylation indices (MI) do not reveal any significant differences at nine DMRs among the conception groups in neither MPB, UCB nor in ACT. The only slightly variable DMR was that of MEST. Here the mean MI was higher in UCB and MPB of IVF cases (mean MI+/-SD: 0.41+/-0.03 (UCB) and 0.40+/-0.03 (MPB)) compared to the ICSI (0.38+/-0.03, p=0.003 (UCB); 0.37+/-0.04, p=0.0007 (MPB)) or spontaneous cases (0.38+/-0.03, p=0.003 (UCB); 0.38+/-0.04, p=0.02 (MPB)). Weak but suggestive correlations between DMRs were, however, found between MPB, UCB and ACT. CONCLUSION This study supports the notion that children conceived by ART do not show a higher degree of imprint variability and hence do not have an a priori higher risk for imprinting disorders