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Congenital heart defects (CHD) occur in 40% of patients with trisomy 21, while the other 60% have a structurally normal heart. This suggests that the increased dosage of genes on chromosome 21 is a risk factor for abnormal heart development. Interaction of genes on chromosome 21 or their gene products with certain alleles of genes on other chromosomes could contribute to CHD. Here, we identified a pair of monozygotic twins with trisomy 21 but discordant for a ventricular septal defect and epilepsy. Twin-zygosity was confirmed by microsatellite genotyping. We hypothesized that some genetic differences from post-twinning mutations caused the discordant phenotypes. Thus, next generation sequencing (NGS) technologies were applied to sequence both whole genome and exome of their leukocytes. The post-analyses of the sequencing data revealed 21 putative discordant exonic variants between the twins from either genome or exome data. However, of the 15 variants chosen for validation with conventional Sanger sequencing, these candidate variants showed no differences in both twins. The fact that no discordant DNA variants were found suggests that sequence differences of DNA from leukocytes of monozygotic twins might be extremely rare. It also emphasizes the limitation of the current NGS technology in identifying causative genes for discordant phenotypes in monozygotic twins. [ABSTRACT FROM AUTHOR]

Two syndromic cognitive impairment disorders have very similar craniofacial dysmorphisms. One is caused by mutations of SATB2, a transcription regulator and the other by heterozygous mutations leading to premature stop codons in UPF3B, encoding a member of the nonsense-mediated mRNA decay complex. Here we demonstrate that the products of these two causative genes function in the same pathway. We show that the SATB2 nonsense mutation in our patient leads to a truncated protein that localizes to the nucleus, forms a dimer with wild-type SATB2 and interferes with its normal activity. This suggests that the SATB2 nonsense mutation has a dominant negative effect. The patient’s leukocytes had significantly decreased UPF3B mRNA compared to controls. This effect was replicated both in vitro, where siRNA knockdown of SATB2 in HEK293 cells resulted in decreased UPF3B expression, and in vivo, where embryonic tissue of Satb2 knockout mice showed significantly decreased Upf3b expression. Furthermore, chromatin immunoprecipitation demonstrates that SATB2 binds to the UPF3B promoter, and a luciferase reporter assay confirmed that SATB2 expression significantly activates gene transcription using the UPF3B promoter. These findings indicate that SATB2 activates UPF3B expression through binding to its promoter. This study emphasizes the value of recognizing disorders with similar clinical phenotypes to explore underlying mechanisms of genetic interaction. [ABSTRACT FROM AUTHOR]

Isolated cleft palate (CP) is common in humans and has complex genetic etiologies. Many genes have been found to contribute to CP, but the full spectrum of genes remains unknown. PCR-sequencing of the entire coding regions and the 3′ untranslated region (UTR) of the platelet-derived growth factor receptor alpha (PDGFRa) and the microRNA (miR), miR-140 identified seven novel single base-pair substitutions in the PDGFRa in 9/102 patients with CP (8.8%), compared with 5/500 ethnic-matched unaffected controls (1%) (the two-tailed P-value<0.0001). Of these seven, four were missense mutations in the coding regions and three in the 3′UTR. Frequencies of four changes (three in coding, one in 3′UTR) were statistically different from those of controls (P-value<0.05). The c.*34G>A was identified in 1/102 cases and 0/500 controls. This position is conserved in primates and located 10 bp away from a predicted binding site for the miR-140. Luciferase assay revealed that, in the presence of miR-140, the c.*34G>A significantly repressed luciferase activity compared with that of the wild type, suggesting functional significance of this variant. This is the first study providing evidence supporting a role of PDGFRa in human CP. [ABSTRACT FROM AUTHOR]