Segmental paternal uniparental disomy (patUPD) of 14q32 with abnormal methylation elicits the characteristic features of complete patUPD14.

Uniparental disomy (UPD) for chromosome 14 is associated with well-recognized phenotypes, depending on the parent of origin. Studies in mouse models and human patients have implicated the involvement of the distal region of the long arm of chromosome 14 in the distinctive phenotypes. This involvement is supported by the identification of an imprinting cluster at chromosome 14q32, encompassing the differentially methylated regions (DMRs), IG-DMR and MEG3-DMR, as well as the maternally expressed genes GTL2, DIO3, and RTL1 and the paternally expressed genes DLK1, RTL1as, and MEG8. Here we report on a preterm female infant with distal segmental paternal UPD14 (upd(14)pat) of 14q32-14q32.33, which resulted in thoracic deformity secondary to rib abnormalities ("coat-hanger" rib sign), polyhydramnios, and other congenital abnormalities characteristically described in cases of complete upd(14)pat. Microsatellite investigation demonstrated UPD of markers D14S250 and D14S1010, encompassing a approximately 3.5 Mb region of distal 14q and involving the imprinting cluster. This case provided insight into the etiology of the phenotypic effects of upd(14)pat, prompting methylation analysis of the GTL2 promoter and the DMR between GTL2 and DLK1. We compare the physical findings seen in this case with those of patients with other causes of abnormal methylation of 14q32, which consistently result in certain distinct clinical features, regardless of the cytogenetic and molecular etiology.

A new direction for prenatal chromosome microarray testing: software-targeting for detection of clinically significant chromosome imbalance without equivocal findings.

Purpose. To design and validate a prenatal chromosomal microarray testing strategy that moves away from size-based detection thresholds, towards a more clinically relevant analysis, providing higher resolution than G-banded chromosomes but avoiding the detection of copy number variants (CNVs) of unclear prognosis that cause parental anxiety. Methods. All prenatal samples fulfilling our criteria for karyotype analysis (n = 342) were tested by chromosomal microarray and only CNVs of established deletion/duplication syndrome regions and any other CNV >3 Mb were detected and reported. A retrospective full-resolution analysis of 249 of these samples was carried out to ascertain the performance of this testing strategy. Results. Using our prenatal analysis, 23/342 (6.7%) samples were found to be abnormal. Of the remaining samples, 249 were anonymized and reanalyzed at full-resolution; a further 46 CNVs were detected in 44 of these cases (17.7%). None of these additional CNVs were of clear clinical significance. Conclusion. This prenatal chromosomal microarray strategy detected all CNVs of clear prognostic value and did not miss any CNVs of clear clinical significance. This strategy avoided both the problems associated with interpreting CNVs of uncertain prognosis and the parental anxiety that are a result of such findings.

Reduced dosage of ERF causes complex craniosynostosis in humans and mice and links ERK1/2 signaling to regulation of osteogenesis.

The extracellular signal-related kinases 1 and 2 (ERK1/2) are key proteins mediating mitogen-activated protein kinase signaling downstream of RAS: phosphorylation of ERK1/2 leads to nuclear uptake and modulation of multiple targets. Here, we show that reduced dosage of ERF, which encodes an inhibitory ETS transcription factor directly bound by ERK1/2 (refs. 2,3,4,5,6,7), causes complex craniosynostosis (premature fusion of the cranial sutures) in humans and mice. Features of this newly recognized clinical disorder include multiple-suture synostosis, craniofacial dysmorphism, Chiari malformation and language delay. Mice with functional Erf levels reduced to ∼30% of normal exhibit postnatal multiple-suture synostosis; by contrast, embryonic calvarial development appears mildly delayed. Using chromatin immunoprecipitation in mouse embryonic fibroblasts and high-throughput sequencing, we find that ERF binds preferentially to elements away from promoters that contain RUNX or AP-1 motifs. This work identifies ERF as a novel regulator of osteogenic stimulation by RAS-ERK signaling, potentially by competing with activating ETS factors in multifactor transcriptional complexes.

How genetically heterogeneous is Kabuki syndrome?: MLL2 testing in 116 patients, review and analyses of mutation and phenotypic spectrum.

MLL2 mutations are detected in 55 to 80% of patients with Kabuki syndrome (KS). In 20 to 45% patients with KS, the genetic basis remains unknown, suggesting possible genetic heterogeneity. Here, we present the largest yet reported cohort of 116 patients with KS. We identified MLL2 variants in 74 patients, of which 47 are novel and a majority are truncating. We show that pathogenic missense mutations were commonly located in exon 48. We undertook a systematic facial KS morphology study of patients with KS at our regional dysmorphology meeting. Our data suggest that nearly all patients with typical KS facial features have pathogenic MLL2 mutations, although KS can be phenotypically variable. Furthermore, we show that MLL2 mutation-positive KS patients are more likely to have feeding problems, kidney anomalies, early breast bud development, joint dislocations and palatal malformations in comparison with MLL2 mutation-negative patients. Our work expands the mutation spectrum of MLL2 that may help in better understanding of this molecule, which is important in gene expression, epigenetic control of active chromatin states, embryonic development and cancer. Our analyses of the phenotype indicates that MLL2 mutation-positive and -negative patients differ systematically, and genetic heterogeneity of KS is not as extensive as previously suggested. Moreover, phenotypic variability of KS suggests that MLL2 testing should be considered even in atypical patients.

Polymicrogyria and deletion 22q11.2 syndrome: window to the etiology of a common cortical malformation.

Several brain malformations have been described in rare patients with the deletion 22q11.2 syndrome (DEL22q11) including agenesis of the corpus callosum, pachygyria or polymicrogyria (PMG), cerebellar anomalies and meningomyelocele, with PMG reported most frequently. In view of our interest in the causes of PMG, we reviewed clinical data including brain-imaging studies on 21 patients with PMG associated with deletion 22q11.2 and another 11 from the literature. We found that the cortical malformation consists of perisylvian PMG of variable severity and frequent asymmetry with a striking predisposition for the right hemisphere (P = 0.008). This and other observations suggest that the PMG may be a sequela of abnormal embryonic vascular development rather than a primary brain malformation. We also noted mild cerebellar hypoplasia or mega-cisterna magna in 8 of 24 patients. Although this was not the focus of the present study, mild cerebellar anomalies are probably the most common brain malformation associated with DEL22q11.

Monozygotic twins discordant for frontonasal malformation.

Frontonasal malformation (FNM), also known as the median cleft face syndrome, encompasses a spectrum of phenotypes that are believed to result from a single underlying aetiology. Over the course of two decades, the Craniofacial Unit at the Radcliffe Infirmary, Oxford has been involved in the management of six same-sex twins where only a single twin is affected. With local ethical committee approval, five sets of twins were traced and consented to participation in this study. Monozygosity of all five twin pairs was confirmed, and the clinical features were reviewed. We discuss the mechanistic relationship between FNM and the twinning process and the genetic implications of this association.