Clinical features associated with copy number variations of the 14q32 imprinted gene cluster.

Uniparental disomy (UPD) for imprinted chromosomes can cause abnormal phenotypes due to absent or overexpression of imprinted genes. UPD(14)pat causes a unique constellation of features including thoracic skeletal anomalies, polyhydramnios, placentomegaly, and limited survival; its hypothesized cause is overexpression of paternally expressed RTL1, due to absent regulatory effects of maternally expressed RTL1as. UPD(14)mat causes a milder condition with hypotonia, growth failure, and precocious puberty; its hypothesized cause is absence of paternally expressed DLK1. To more clearly establish how gains and losses of imprinted genes can cause disease, we report six individuals with copy number variations of the imprinted 14q32 region identified through clinical microarray-based comparative genomic hybridization. Three individuals presented with UPD(14)mat-like phenotypes (Temple syndrome) and had apparently de novo deletions spanning the imprinted region, including DLK1. One of these deletions was shown to be on the paternal chromosome. Two individuals with UPD(14)pat-like phenotypes had 122-154kb deletions on their maternal chromosomes that included RTL1as but not the differentially methylated regions that regulate imprinted gene expression, providing further support for RTL1 overexpression as a cause for the UPD(14)pat phenotype. The sixth individual is tetrasomic for a 1.7Mb segment, including the imprinted region, and presents with intellectual disability and seizures but lacks significant phenotypic overlap with either UPD(14) syndrome. Therefore, the 14q32 imprinted region is dosage sensitive, with deletions of different critical regions causing UPD(14)mat- and UPD(14)pat-like phenotypes, while copy gains are likely insufficient to recapitulate these phenotypes.

Investigation of NRXN1 deletions: clinical and molecular characterization.

Deletions at 2p16.3 involving exons of NRXN1 are associated with susceptibility for autism and schizophrenia, and similar deletions have been identified in individuals with developmental delay and dysmorphic features. We have identified 34 probands with exonic NRXN1 deletions following referral for clinical microarray-based comparative genomic hybridization. To more firmly establish the full phenotypic spectrum associated with exonic NRXN1 deletions, we report the clinical features of 27 individuals with NRXN1 deletions, who represent 23 of these 34 families. The frequency of exonic NRXN1 deletions among our postnatally diagnosed patients (0.11%) is significantly higher than the frequency among reported controls (0.02%; P = 6.08 × 10(-7) ), supporting a role for these deletions in the development of abnormal phenotypes. Generally, most individuals with NRXN1 exonic deletions have developmental delay (particularly speech), abnormal behaviors, and mild dysmorphic features. In our cohort, autism spectrum disorders were diagnosed in 43% (10/23), and 16% (4/25) had epilepsy. The presence of NRXN1 deletions in normal parents and siblings suggests reduced penetrance and/or variable expressivity, which may be influenced by genetic, environmental, and/or stochastic factors. The pathogenicity of these deletions may also be affected by the location of the deletion within the gene. Counseling should appropriately represent this spectrum of possibilities when discussing recurrence risks or expectations for a child found to have a deletion in NRXN1.

High-resolution array CGH defines critical regions and candidate genes for microcephaly, abnormalities of the corpus callosum, and seizure phenotypes in patients with microdeletions of 1q43q44.

Microdeletions of 1q43q44 result in a recognizable clinical disorder characterized by moderate to severe intellectual disability (ID) with limited or no expressive speech, characteristic facial features, hand and foot anomalies, microcephaly (MIC), abnormalities (agenesis/hypogenesis) of the corpus callosum (ACC), and seizures (SZR). Critical regions have been proposed for some of the more prominent features of this disorder such as MIC and ACC, yet conflicting data have prevented precise determination of the causative genes. In this study, the largest of pure interstitial and terminal deletions of 1q43q44 to date, we characterized 22 individuals by high-resolution oligonucleotide microarray-based comparative genomic hybridization. We propose critical regions and candidate genes for the MIC, ACC, and SZR phenotypes associated with this microdeletion syndrome. Three cases with MIC had small overlapping or intragenic deletions of AKT3, an isoform of the protein kinase B family. The deletion of only AKT3 in two cases implicates haploinsufficiency of this gene in the MIC phenotype. Likewise, based on the smallest region of overlap among the affected individuals, we suggest a critical region for ACC that contains ZNF238, a transcriptional and chromatin regulator highly expressed in the developing and adult brain. Finally, we describe a critical region for the SZR phenotype which contains three genes (FAM36A, C1ORF199, and HNRNPU). Although ~90% of cases in this study and in the literature fit these proposed models, the existence of phenotypic variability suggests other mechanisms such as variable expressivity, incomplete penetrance, position effects, or multigenic factors could account for additional complexity in some cases.

Impact of genotype-first diagnosis: the detection of microdeletion and microduplication syndromes with cancer predisposition by aCGH.

BACKGROUND: The use of microarray-based comparative genomic hybridization has allowed the genetic diagnosis of some conditions before their full clinical presentation. This "genotype-first" diagnosis has the most clinical implications for genomic alterations that confer an elevated risk of cancer. In these cases, diagnosis before the manifestation of the patient's full phenotype dramatically impacts genetic counseling, clinical management, and eventual prognosis and survivability. METHODS: Using microarray-based comparative genomic hybridization, we tested 18,437 individuals with indications such as developmental disabilities and congenital anomalies. RESULTS: We identified 34 (0.18%) individuals with DNA copy number gains or losses that encompassed gene regions associated with recognized genetic conditions with an increased risk for cancer. Three of the 34 individuals (8.8%) had a previously abnormal cytogenetic study which microarray-based comparative genomic hybridization confirmed and/or further characterized. Seven of the 34 individuals (20.6%) either had the correct disease specified in the clinical indication for study or had clinical features highly indicative of that syndrome. The remaining 24 patients (70.6%) had indications for study that were not specific to the diagnosed syndrome, such as "developmental delay" or "dysmorphic features." CONCLUSIONS: The ability of microarray-based comparative genomic hybridization to rapidly and objectively interrogate the genome for chromosomal imbalances has led to the opportunity to optimize medical management and outcome. This has an even more profound impact and clinical utility in conditions associated with cancer predisposition syndromes.