Supplementary Material for: Maternal Hypomethylation of KvDMR in a Monozygotic Male Twin Pair Discordant for Beckwith-Wiedemann Syndrome

Beckwith-Wiedemann syndrome (BWS; OMIM 130650) is a heterogeneous overgrowth syndrome characterized by visceromegaly, macroglossia, tumor predisposition, and other congenital abnormalities. BWS is usually associated with abnormalities of chromosome 11p15, including (epi)genetic changes, paternal disomy and point mutations. A number of identical twin pairs, mostly female, have been reported to be clinically discordant for BWS. Studies of monozygotic twins discordant for BWS provide more information about failure in the DNA methylation maintenance machinery during very early embryonic development. Here, we report a case of monozygotic male twins discordant for BWS phenotype. Methylation analysis of the 2 imprinted domains at 11p15.5 (H19DMR and KvDMR) was performed by methylation-specific MLPA and pyrosequencing of DNA extracted from peripheral blood and buccal swabs of both twins. Hypomethylation at KvDMR was identified in both cell types of the affected twin, whereas his healthy brother presented hypomethylation only in blood cells and a normal methylation profile in buccal swab. For diagnostic purposes, it is important to remember that twins can share fetal circulation and possibly share hematopoietic stem cells early in development; therefore, the affected and unaffected twins can share an epigenotype that will resemble partial hypomethylation. If a patient is a twin, it is valuable to obtain a sample from a tissue other than blood

Supplementary Material for: Novel Mutation and Structural RNA Analysis of the Noncoding RNase <b><i>MRP</i></b> Gene in Cartilage-Hair Hypoplasia

Cartilage-hair hypoplasia (CHH) is an autosomal recessive disorder which is characterized by bone metaphysis anomalies with manifestations that include short stature, defective cellular immunity, and predisposition to several cancers. It is caused by mutations in <i>RMRP</i>, which is transcribed as an RNA component of the mitochondrial RNA-processing ribonuclease. We report the clinical and molecular data of a Moroccan patient with CHH. Sequencing of <i>RMRP</i> identified 2 mutations in the patient: the known mutation g.97G>A and the variation g.27G>C, which has not been reported previously. Given the high mutational heterogeneity, the high frequency of variations in the region, and the fact that <i>RMRP</i> is a non-coding gene, assigning the pathogenicity to <i>RMRP</i> mutations remains a difficult task. Therefore, we compared the characteristics of the primary and secondary structures of mutated RMRP sequences. The location of our mutations within the secondary structure of the RMRP molecule revealed that the novel g.27G>C mutation causes a disruption in the Watson-Crick base pairing, which results in an impairment of a highly conserved P3 domain. Our work prompts considering the consequences of novel <i>RMRP</i> nucleotide variations on conserved RNA structures to gain insights into the pathogenicity of mutations