Amy M. Breman

SHANK3 overexpression causes manic-like behaviour with unique pharmacogenetic properties

Mutations in SHANK3 and large duplications of the region spanning SHANK3 both cause a spectrum of neuropsychiatric disorders, indicating that proper SHANK3 dosage is critical for normal brain function. However, SHANK3 overexpression per se has not been established as a cause of human disorders because 22q13 duplications involve several genes. Here we report that Shank3 transgenic mice modelling a human SHANK3 duplication exhibit manic-like behaviour and seizures consistent with synaptic excitatory/inhibitory imbalance. We also identified two patients with hyperkinetic disorders carrying the smallest SHANK3-spanning duplications reported so far. These findings indicate that SHANK3 overexpression causes a hyperkinetic neuropsychiatric disorder. To probe the mechanism underlying the phenotype, we generated a Shank3 in vivo interactome and found that Shank3 directly interacts with the Arp2/3 complex to increase F-actin levels in Shank3 transgenic mice. The mood-stabilizing drug valproate, but not lithium, rescues the manic-like behaviour of Shank3 transgenic mice raising the possibility that this hyperkinetic disorder has a unique pharmacogenetic profile.

Chromosome 8p23.1 deletions as a cause of complex congenital heart defects and diaphragmatic hernia.

Recurrent interstitial deletion of a region of 8p23.1 flanked by the low copy repeats 8p‐OR‐REPD and 8p‐OR‐REPP is associated with a spectrum of anomalies that can include congenital heart malformations and congenital diaphragmatic hernia (CDH). Haploinsufficiency of GATA4 is thought to play a critical role in the development of these birth defects. We describe two individuals and a monozygotic twin pair discordant for anterior CDH all of whom have complex congenital heart defects caused by this recurrent interstitial deletion as demonstrated by array comparative genomic hybridization. To better define the genotype/phenotype relationships associated with alterations of genes on 8p23.1, we review the spectrum of congenital heart and diaphragmatic defects that have been reported in individuals with isolated GATA4 mutations and interstitial, terminal, and complex chromosomal rearrangements involving the 8p23.1 region. Our findings allow us to clearly define the CDH minimal deleted region on chromosome 8p23.1 and suggest that haploinsufficiency of other genes, in addition to GATA4, may play a role in the severe cardiac and diaphragmatic defects associated with 8p23.1 deletions. These findings also underscore the importance of conducting a careful cytogenetic/molecular analysis of the 8p23.1 region in all prenatal and postnatal cases involving congenital defects of the heart and/or diaphragm.

Prenatal chromosomal microarray analysis in a diagnostic laboratory; experience with >1000 cases and review of the literature

To evaluate the results of prenatal chromosomal microarray analysis (CMA) on >1000 fetal samples referred for testing at our institution and to compare these data to published reports.

Rapid prenatal diagnosis using uncultured amniocytes and oligonucleotide array CGH

Oligonucleotide‐based array comparative genomic hybridization (array CGH) is an established method for detecting chromosomal abnormalities. Here, we explored the feasibility of using DNA extracted from uncultured amniocytes in amniotic fluid for array CGH on an oligonucleotide array platform.

Interphase FISH Demonstrates that Human Adipose Stromal Cells Maintain a High Level of Genomic Stability in Long-Term Culture

Human adipose stromal cells (ASCs) reside within the stromal-vascular fraction (SVF) in fat tissue, can be readily isolated, and include stem-like cells that may be useful for therapy. An important consideration for clinical application and functional studies of stem/progenitor cells is their capacity to maintain chromosome stability in culture. In this study, cultured ASC populations and ASC clones were evaluated at intervals for maintenance of chromosome stability. Uncultured SVF (uSVF) cells were included for comparison. G-banded chromosome analysis demonstrated that ASCs are diploid and have a normal karyotype. However since only approximately 20 cells are examined, low levels of chromosome instability would not be detected. To increase detection sensitivity, fluorescence in situ hybridization was employed, to permit chromosome enumeration in larger numbers of interphase cells. Seven cultured ASC populations, two ASC clones and four uSVF samples were examined. Chromosome X and 17 probes identified diploid, tetraploid, and aneuploid interphase cells. Both cultured ASC populations [up to approximately 35 Population Doublings (PDs)] and uSVF cells exhibited a similar level of diploidy (97.8% n = 6,355 and 98.83% n = 1,197, respectively) and numerical abnormalities, suggesting that cultured ASCs are genomically stable and supporting their suitability for transplantation applications. In comparison, cultured primary human chorionic villus cells exhibited marked genomic instability resulting in an 11.6% tetraploidy rate after 8-10 PD. Thus effects of culture on genomic stability may be cell type dependent and should be tested by appropriately scaled interphase fluorescence in situ hybridization analysis in any ex vivo expanded cell population destined for transplantation.

Regional genomic instability predisposes to complex dystrophin gene rearrangements

Mutations in the dystrophin gene (DMD) cause Duchenne and Becker muscular dystrophies and the majority of cases are due to DMD gene rearrangements. Despite the high incidence of these aberrations, little is known about their causative molecular mechanism(s). We examined 792 DMD/BMD clinical samples by oligonucleotide array-CGH and report on the junction sequence analysis of 15 unique deletion cases and three complex intragenic rearrangements to elucidate potential underlying mechanism(s). Furthermore, we present three cases with intergenic rearrangements involving DMD and neighboring loci. The cases with intragenic rearrangements include an inversion with flanking deleted sequences; a duplicated segment inserted in direct orientation into a deleted region; and a splicing mutation adjacent to a deletion. Bioinformatic analysis demonstrated that 7 of 12 breakpoints combined among 3 complex cases aligned with repetitive sequences, as compared to 4 of 30 breakpoints for the 15 deletion cases. Moreover, the inversion/deletion case may involve a stem-loop structure that has contributed to the initiation of this rearrangement. For the duplication/deletion and splicing mutation/deletion cases, the presence of the first mutation, either a duplication or point mutation, may have elicited the deletion events in an attempt to correct preexisting mutations. While NHEJ is one potential mechanism for these complex rearrangements, the highly complex junction sequence of the inversion/deletion case suggests the involvement of a replication-based mechanism. Our results support the notion that regional genomic instability, aided by the presence of repetitive elements, a stem-loop structure, and possibly preexisting mutations, may elicit complex rearrangements of the DMD gene.

OEIS complex associated with chromosome 1p36 deletion: A case report and review†

OEIS complex (Omphalocele, Exstrophy of the cloaca, Imperforate anus, and Spine abnormalities) is a rare defect with estimated incidence of 1 in 200,000 live births. Most cases are sporadic, with no obvious cause. However, it has been rarely reported in patients with family members having similar malformations or with chromosomal anomalies. In addition, OEIS complex has been observed in association with environmental exposures, twinning, and in vitro fertilization. Monosomy 1p36 is the most common terminal deletion syndrome, with a prevalence of 1 in 5,000 newborns. It is characterized by specific facial features, developmental delay, and heart, skeletal, genitourinary, and neurological defects. We describe an infant with OEIS complex and 1p36 deletion who had features of both disorders, including omphalocele, cloacal exstrophy, imperforate anus, sacral multiple segmentation, renal malposition and malrotation, genital anomalies, diastasis of the symphysis pubis, microbrachycephaly, large anterior fontanel, cardiac septal defects, rib fusion, a limb deformity, developmental delay, and typical facial features. Chromosomal microarray analysis detected a 2.4 Mb terminal deletion of chromosome 1p. This is the first reported case with OEIS complex in association with a chromosome 1p36 deletion.

MECP2 duplications in six patients with complex sex chromosome rearrangements

Duplications of the Xq28 chromosome region resulting in functional disomy are associated with a distinct clinical phenotype characterized by infantile hypotonia, severe developmental delay, progressive neurological impairment, absent speech, and proneness to infections. Increased expression of the dosage-sensitive MECP2 gene is considered responsible for the severe neurological impairments observed in affected individuals. Although cytogenetically visible duplications of Xq28 are well documented in the published literature, recent advances using array comparative genomic hybridization (CGH) led to the detection of an increasing number of microduplications spanning MECP2. In rare cases, duplication results from intrachromosomal rearrangement between the X and Y chromosomes. We report six cases with sex chromosome rearrangements involving duplication of MECP2. Cases 1–4 are unbalanced rearrangements between X and Y, resulting in MECP2 duplication. The additional Xq material was translocated to Yp in three cases (cases 1–3), and to the heterochromatic region of Yq12 in one case (case 4). Cases 5 and 6 were identified by array CGH to have a loss in copy number at Xp and a gain in copy number at Xq28 involving the MECP2 gene. In both cases, fluorescent in situ hybridization (FISH) analysis revealed a recombinant X chromosome containing the duplicated material from Xq28 on Xp, resulting from a maternal pericentric inversion. These cases add to a growing number of MECP2 duplications that have been detected by array CGH, while demonstrating the value of confirmatory chromosome and FISH studies for the localization of the duplicated material and the identification of complex rearrangements.

Detection of ≥1 Mb microdeletions and microduplications in a single cell using custom oligonucleotide arrays

High resolution detection of genomic copy number abnormalities in a single cell is relevant to preimplantation genetic diagnosis and potentially to noninvasive prenatal diagnosis. Our objective is to develop a reliable array comparative genomic hybridization (CGH) platform to detect genomic imbalances as small as ~1 Mb in a single cell.

Identifying and genotyping transgene integration loci

The random germline integration of genetically engineered transgenes has been a powerful technique to study the role of particular genes in variety of biological processes. Although the identification of the transgene insertion site is often not essential for functional analysis of the transgene, identifying the site can have practical benefit. Enabling one to distinguish between animals that are homozygous or hemizygous for the transgene locus could facilitate breeding strategies to produce animals with a large number of genetic markers. Furthermore, founder lines generated with the same transgene construct may exhibit different phenotypes and levels of transgene expression depending on the site of integration. The goal of this report was to develop a rapid protocol for the identification and verification of transgene insertion sites. To identify host genomic sequences at the coagulation Factor X transgene integration site, DNA from a tail snip of the transgenic mouse was digested with NcoI and circularized using T4 DNA ligase. Using appropriately positioned PCR primers annealing to a transgene fragment distal to a terminal transgene restriction site (NcoI), one could amplify a fragment containing the transgene terminal region and extending into the flanking genomic sequence at the insertion site. DNA sequence determination of the amplicon permitted identification of the insertion site using a BLASTN search. FISH analysis of a metaphase spread of primary fibroblasts derived from the transgenic mouse was consistent with the identification of insertion site near the end of mouse chromosome 14. Identification of transgene insertion sites will facilitate genotyping strategies useful for the construction of mice with multiple engineered genetic markers and to distinguish among different founder lines generated by the same transgene. Furthermore, identification of the insertion site is necessary to analyze unexpected phenotypes that might be caused by insertional inactivation of an endogenous gene.