Whole exome sequencing is necessary to clarify ID/DD cases with de novo copy number variants of uncertain significance: Two proof-of-concept examples.

Whole exome sequencing (WES) is a powerful tool to identify clinically undefined forms of intellectual disability/developmental delay (ID/DD), especially in consanguineous families. Here we report the genetic definition of two sporadic cases, with syndromic ID/DD for whom array-Comparative Genomic Hybridization (aCGH) identified a de novo copy number variant (CNV) of uncertain significance. The phenotypes included microcephaly with brachycephaly and a distinctive facies in one proband, and hypotonia in the legs and mild ataxia in the other. WES allowed identification of a functionally relevant homozygous variant affecting a known disease gene for rare syndromic ID/DD in each proband, that is, c.1423C>T (p.Arg377*) in the Trafficking Protein Particle Complex 9 (TRAPPC9), and c.154T>C (p.Cys52Arg) in the Very Low Density Lipoprotein Receptor (VLDLR). Four mutations affecting TRAPPC9 have been previously reported, and the present finding further depicts this syndromic form of ID, which includes microcephaly with brachycephaly, corpus callosum hypoplasia, facial dysmorphism, and overweight. VLDLR-associated cerebellar hypoplasia (VLDLR-CH) is characterized by non-progressive congenital ataxia and moderate-to-profound intellectual disability. The c.154T>C (p.Cys52Arg) mutation was associated with a very mild form of ataxia, mild intellectual disability, and cerebellar hypoplasia without cortical gyri simplification. In conclusion, we report two novel cases with rare causes of autosomal recessive ID, which document how interpreting de novo array-CGH variants represents a challenge in consanguineous families; as such, clinical WES should be considered in diagnostic testing. © 2016 Wiley Periodicals, Inc.

(Epi)genotype-phenotype correlations in Beckwith-Wiedemann syndrome.

Beckwith-Wiedemann syndrome (BWS) is characterized by cancer predisposition, overgrowth and highly variable association of macroglossia, abdominal wall defects, nephrourological anomalies, nevus flammeus, ear malformations, hypoglycemia, hemihyperplasia, and organomegaly. BWS molecular defects, causing alteration of expression or activity of the genes regulated by two imprinting centres (IC) in the 11p15 chromosomal region, are also heterogeneous. In this paper we define (epi)genotype-phenotype correlations in molecularly confirmed BWS patients. The characteristics of 318 BWS patients with proven molecular defect were compared among the main four molecular subclasses: IC2 loss of methylation (IC2-LoM, n=190), IC1 gain of methylation (IC1-GoM, n=31), chromosome 11p15 paternal uniparental disomy (UPD, n=87), and cyclin-dependent kinase inhibitor 1C gene (CDKN1C) variants (n=10). A characteristic growth pattern was found in each group; neonatal macrosomia was almost constant in IC1-GoM, postnatal overgrowth in IC2-LoM, and hemihyperplasia more common in UPD (P<0.001). Exomphalos was more common in IC2/CDKN1C patients (P<0.001). Renal defects were typical of UPD/IC1 patients, uretheral malformations of IC1-GoM cases (P<0.001). Ear anomalies and nevus flammeus were associated with IC2/CDKN1C genotype (P<0.001). Macroglossia was less common among UPD patients (P<0.001). Wilms' tumor was associated with IC1-GoM or UPD and never observed in IC2-LoM patients (P<0.001). Hepatoblastoma occurred only in UPD cases. Cancer risk was lower in IC2/CDKN1C, intermediate in UPD, and very high in IC1 cases (P=0.009). In conclusion, (epi)genotype-phenotype correlations define four different phenotypic BWS profiles with some degree of clinical overlap. These observations impact clinical care allowing to move toward (epi) genotype-based follow-up and cancer screening.

A novel 3q29 deletion associated with autism, intellectual disability, psychiatric disorders, and obesity.

Copy number variation (CNV) has been associated with a variety of neuropsychiatric disorders, including intellectual disability/developmental delay (ID/DD), autism spectrum disorder (ASD), and schizophrenia (SCZ). Often, individuals carrying the same pathogenic CNV display high clinical variability. By array-CGH analysis, we identified a novel familial 3q29 deletion (1.36 Mb), centromeric to the 3q29 deletion region, which manifests with variable expressivity. The deletion was identified in a 3-year-old girl diagnosed with ID/DD and autism and segregated in six family members, all affected by severe psychiatric disorders including schizophrenia, major depression, anxiety disorder, and personality disorder. All individuals carrying the deletion were overweight or obese, and anomalies compatible with optic atrophy were observed in three out of four cases examined. Amongst the 10 genes encompassed by the deletion, the haploinsufficiency of Optic Atrophy 1 (OPA1), associated with autosomal dominant optic atrophy, is likely responsible for the ophthalmological anomalies. We hypothesize that the haploinsufficiency of ATPase type 13A4 (ATP13A4) and/or Hairy/Enhancer of Split Drosophila homolog 1 (HES1) contribute to the neuropsychiatric phenotype, while HES1 deletion might underlie the overweight/obesity. In conclusion, we propose a novel contiguous gene syndrome due to a proximal 3q29 deletion variably associated with autism, ID/DD, psychiatric traits and overweight/obesity.

The molecular function and clinical phenotype of partial deletions of the IGF2/H19 imprinting control region depends on the spatial arrangement of the remaining CTCF-binding sites.

At chromosome 11p15.5, the imprinting centre 1 (IC1) controls the parent of origin-specific expression of the IGF2 and H19 genes. The 5 kb IC1 region contains multiple target sites (CTS) for the zinc-finger protein CTCF, whose binding on the maternal chromosome prevents the activation of IGF2 and allows that of H19 by common enhancers. CTCF binding helps maintaining the maternal IC1 methylation-free, whereas on the paternal chromosome gamete-inherited DNA methylation inhibits CTCF interaction and enhancer-blocking activity resulting in IGF2 activation and H19 silencing. Maternally inherited 1.4-2.2 kb deletions are associated with methylation of the residual CTSs and Beckwith-Wiedemann syndrome, although with different penetrance and expressivity. We explored the relationship between IC1 microdeletions and phenotype by analysing a number of previously described and novel mutant alleles. We used a highly quantitative assay based on next generation sequencing to measure DNA methylation in affected families and analysed enhancer-blocking activity and CTCF binding in cultured cells. We demonstrate that the microdeletions mostly affect IC1 function and CTCF binding by changing CTS spacing. Thus, the extent of IC1 inactivation and the clinical phenotype are influenced by the arrangement of the residual CTSs. A CTS spacing similar to the wild-type allele results in moderate IC1 inactivation and is associated with stochastic DNA methylation of the maternal IC1 and incomplete penetrance. Microdeletions with different CTS spacing display severe IC1 inactivation and are associated with IC1 hypermethylation and complete penetrance. Careful characterization of the IC1 microdeletions is therefore needed to predict recurrence risks and phenotypical outcomes.

The KCNQ1OT1 imprinting control region and non-coding RNA: new properties derived from the study of Beckwith-Wiedemann syndrome and Silver-Russell syndrome cases.

A cluster of imprinted genes at chromosome 11p15.5 is associated with the growth disorders, Silver-Russell syndrome (SRS) and Beckwith-Wiedemann syndrome (BWS). The cluster is divided into two domains with independent imprinting control regions (ICRs). We describe two maternal 11p15.5 microduplications with contrasting phenotypes. The first is an inverted and in cis duplication of the entire 11p15.5 cluster associated with the maintenance of genomic imprinting and with the SRS phenotype. The second is a 160 kb duplication also inverted and in cis, but resulting in the imprinting alteration of the centromeric domain. It includes the centromeric ICR (ICR2) and the most 5' 20 kb of the non-coding KCNQ1OT1 gene. Its maternal transmission is associated with ICR2 hypomethylation and the BWS phenotype. By excluding epigenetic mosaicism, cell clones analysis indicated that the two closely located ICR2 sequences resulting from the 160 kb duplication carried discordant DNA methylation on the maternal chromosome and supported the hypothesis that the ICR2 sequence is not sufficient for establishing imprinted methylation and some other property, possibly orientation-dependent, is needed. Furthermore, the 1.2 Mb duplication demonstrated that all features are present for correct imprinting at ICR2 when this is duplicated and inverted within the entire cluster. In the individuals maternally inheriting the 160 kb duplication, ICR2 hypomethylation led to the expression of a truncated KCNQ1OT1 transcript and to down-regulation of CDKN1C. We demonstrated by chromatin RNA immunopurification that the KCNQ1OT1 RNA interacts with chromatin through its most 5' 20 kb sequence, providing a mechanism likely mediating the silencing activity of this long non-coding RNA.