M. E. Suzanne Lewis

Correction of Hypertriglyceridemia and Impaired Fat Tolerance in Lipoprotein Lipase–Deficient Mice by Adenovirus-Mediated Expression of Human Lipoprotein Lipase

Humans homozygous or heterozygous for mutations in the lipoprotein lipase (LPL) gene demonstrate significant disturbances in plasma lipoproteins, including raised triglyceride (TG) and reduced HDL cholesterol levels. In this study we explored the feasibility of adenovirus-mediated gene replacement therapy for LPL deficiency. A total of 5 x 10(9) plaque-forming units (pfu) of an E1/E3-deleted adenovirus expressing either human LPL (Ad-LPL) or the bacterial beta-galactosidase gene (Ad-LacZ) as a control were administered to mice heterozygous for targeted disruption in the LPL gene (n = 57). Peak expression of total postheparin plasma LPL activity was observed at day 7 in Ad-LPL mice versus Ad-LacZ controls (834 +/- 133 vs 313 +/- 89 mU/mL, P < .01), and correlated with human-specific LPL activity (522 +/- 219 mU/mL) and mass (9214 +/- 782 ng/mL), a change that was significant to 14 and 42 days, respectively. At day 7, plasma TGs were significantly reduced relative to Ad-LacZ mice (0.17 +/- 0.07 vs 1.90 +/- 0.89 mmol/L, P < .01) but returned to endogenous levels by day 42. Ectopic liver expression of human LPL was confirmed by in situ hybridization analysis and from raised LPL activity and mass in liver homogenates. Analysis of plasma lipoprotein composition revealed a marked decrease in VLDL-derived TGs. Severely impaired oral and intravenous fat-load tolerance in LPL-deficient mice was subsequently corrected after Ad-LPL administration and closely paralleled that observed in wild-type mice. These findings suggest that liver-targeted adenovirus-mediated LPL gene transfer offers an effective means for transient correction of altered lipoprotein metabolism and impaired fat tolerance due to LPL deficiency.

Abnormal pericyte recruitment as a cause for pulmonary hypertension in Adams-Oliver syndrome.

Adams–Oliver syndrome (AOS) consists of congenital scalp defects with variable limb defects of unknown pathogenesis. We report on two children with AOS plus additional features including intrauterine growth retardation (IUGR), cutis marmorata telangiectatica congenita (CMTC), pulmonary hypertension (PH), intracranial densities shown in one case to be sites of active bleeding and osteopenia. Autopsy in one case revealed defective vascular smooth muscle cell/pericyte coverage of the vasculature associated with two blood vessel abnormalities. Pericyte absence correlated with vessel dilatation while hyperproliferation of pericytes correlated with vessel stenosis. These findings suggest a unifying pathogenic mechanism for the abnormalities seen in AOS. These and previously reported cases establish that a subset of AOS patients is at high risk for PH.

Phenotypic Correction of Feline Lipoprotein Lipase Deficiency by Adenoviral Gene Transfer

Previous studies have revealed that adenovirus-mediated ectopic liver expression of human LPL (huLPL) can efficiently mediate plasma triacylglycerol (TG) catabolism in mice despite its native expression in adipose and muscle tissue. We aimed to explore the feasibility of liver-directed gene transfer and enzyme replacement for human LPL deficiency in a larger, naturally occurring feline animal model of complete LPL deficiency that is remarkably similar in phenotype to the human disorder. A cohort of LPL-deficient (LPL -/-) cats was given an intravenous injection of 8 x 10(9) PFU/kg of a CMV promoter/enhancer-driven, E1/E3-deleted adenoviral (Ad) vector containing a 1.36-kb huLPL cDNA (Ad-LPL) or reporter alkaline phosphatase gene (Ad-AP). After Ad-LPL administration, active, heparin-releasable huLPL was readily detected along with a 10-fold reduction in plasma TGs, disappearance of plasma TG-rich lipoproteins up to day 14, and enhanced clearance of an excess intravenous fat load on day 9. However, antibody against the huLPL protein was detected on day 14 in cats receiving Ad-LPL and adenovirus-specific neutralizing antibody was present 7 days after gene transfer in both cat cohorts. Tissue-specific expression of the huLPL transgene relative to controls was confirmed by RT-PCR. While huLPL expression was evident in the liver, other tissues including spleen and lung expressed huLPL message, in direct correlation with histological evidence of increased Oil red O (ORO)-positive neutral lipid influx. In contrast, intravenous LPL enzyme replacement therapy (ERT) led to rapid disappearance of 9000 mU/kg of active bovine LPL enzyme from the circulation, with t1/2 occurring at <10 min in two LPL-/- cats. Heparin injection 1 hr later released <10% of the original bovine LPL, further indicating its rapid systemic clearance, inactivation, or degradation as well as its ineffectiveness as a viable therapeutic alternative for complete LPL deficiency. Although LPL gene transfer and expression via this first-generation Ad vector was limited by the immune response against both the human LPL protein and adenovirus our results clearly provide a key advance supporting further development of LPL gene therapy as a viable therapeutic option for clinical LPL deficiency.

Confirmation of linkage in X-linked infantile spasms (West syndrome) and refinement of the disease locus to Xp21.3-Xp22.1

The syndrome of infantile spasms, hypsarrhythmia, and mental retardation (West syndrome) is a classical form of epilepsy, occurring in early infancy, which is etiologically heterogeneous. In rare families, West syndrome is an X‐linked recessive condition, mapped to Xp11.4‐Xpter (MIM 308350). We have identified a multi‐generation family from Western Canada with this rare syndrome of infantile spasms, seen exclusively in male offspring from asymptomatic mothers, thereby confirming segregation as an X‐linked recessive trait. Using highly polymorphic microsatellite CA‐repeat probes evenly distributed over the entire X chromosome, linkage to markers DXS7110, DXS989, DXS1202, and DXS7106 was confirmed, with a maximum LOD score of 3.97 at a Θ of 0.0. The identification of key recombinants refined the disease‐containing interval between markers DXS1226 and the adrenal hypoplasia locus (AHC). This now maps the X‐linked infantile spasms gene locus to chromosome Xp21.3‐Xp22.1 and refines the interval containing the candidate gene to 7.0 cM. Furthermore, this interval overlaps several loci previously linked with either syndromic or non‐syndromic X‐linked mental retardation (XLMR), including one recognized locus implicated in neuroaxonal processing (radixin, RDXP2). Collectively, these studies lend strong support for the presence of one or more genes intrinsic to brain development and function, occurring within the critical interval defined between Xp21.3‐Xp22.1.

Population- and Family-Based Studies Associate the MTHFR Gene with Idiopathic Autism in Simplex Families

Two methylenetetrahydrofolate reductase gene (MTHFR) functional polymorphisms were studied in 205 North American simplex (SPX) and 307 multiplex (MPX) families having one or more children with an autism spectrum disorder. Case–control comparisons revealed a significantly higher frequency of the low-activity 677T allele, higher prevalence of the 677TT genotype and higher frequencies of the 677T-1298A haplotype and double homozygous 677TT/1298AA genotype in affected individuals relative to controls. Family-based association testing demonstrated significant preferential transmission of the 677T and 1298A alleles and the 677T-1298A haplotype to affected offspring. The results were not replicated in MPX families. The results associate the MTHFR gene with autism in SPX families only, suggesting that reduced MTHFR activity is a risk factor for autism in these families.

2p15-p16.1 microdeletion syndrome: molecular characterization and association of the OTX1 and XPO1 genes with autism spectrum disorders.

Reports of unrelated individuals with autism spectrum disorder (ASD) and similar clinical features having overlapping de novo interstitial deletions at 2p15–p16.1 suggest that this region harbors a gene(s) important to the development of autism. We molecularly characterized two such deletions, selecting two genes in this region, exportin 1 (XPO1) and orthodenticle homolog 1 (OTX1) for association studies in three North American cohorts (Autism Spectrum Disorder – Canadian American Research Consortium (ASD–CARC), New York, and Autism Genetic Resource Exchange (AGRE)) and one Italian cohort (Società Italiana per la Ricerca e la Formazione sull’Autismo (SIRFA)) of families with ASD. In XPO1, rs6735330 was associated with autism in all four cohorts (P<0.05), being significant in ASD–CARC cohorts (P-value following false discovery rate correction for multiple testing (PFDR)=1.29 × 10−5), the AGRE cohort (PFDR=0.0011) and the combined families (PFDR=2.34 × 10−9). Similarly, in OTX1, rs2018650 and rs13000344 were associated with autism in ASD–CARC cohorts (PFDR=8.65 × 10−7 and 6.07 × 105, respectively), AGRE cohort (PFDR=0.0034 and 0.015, respectively) and the combined families (PFDR=2.34 × 10−9 and 0.00017, respectively); associations were marginal or insignificant in the New York and SIRFA cohorts. A significant association (PFDR=2.63 × 10−11) was found for the rs2018650G–rs13000344C haplotype. The above three SNPs were associated with severity of social interaction and verbal communication deficits and repetitive behaviors (P-values <0.01). No additional deletions were identified following screening of 798 ASD individuals. Our results indicate that deletion 2p15–p16.1 is not commonly associated with idiopathic ASD, but represents a novel contiguous gene syndrome associated with a constellation of phenotypic features (autism, intellectual disability, craniofacial/CNS dysmorphology), and that XPO1 and OXT1 may contribute to ASD in 2p15–p16.1 deletion cases and non-deletion cases of ASD mapping to this chromosome region.

Large-scale copy number variants (CNVs): Distribution in normal subjects and FISH/real-time qPCR analysis

BackgroundGenomic copy number variants (CNVs) involving >1 kb of DNA have recently been found to be widely distributed throughout the human genome. They represent a newly recognized form of DNA variation in normal populations, discovered through screening of the human genome using high-throughput and high resolution methods such as array comparative genomic hybridization (array-CGH). In order to understand their potential significance and to facilitate interpretation of array-CGH findings in constitutional disorders and cancers, we studied 27 normal individuals (9 Caucasian; 9 African American; 9 Hispanic) using commercially available 1 Mb resolution BAC array (Spectral Genomics). A selection of CNVs was further analyzed by FISH and real-time quantitative PCR (RT-qPCR).ResultsA total of 42 different CNVs were detected in 27 normal subjects. Sixteen (38%) were not previously reported. Thirteen of the 42 CNVs (31%) contained 28 genes listed in OMIM. FISH analysis of 6 CNVs (4 previously reported and 2 novel CNVs) in normal subjects resulted in the confirmation of copy number changes for 1 of 2 novel CNVs and 2 of 4 known CNVs. Three CNVs tested by FISH were further validated by RT-qPCR and comparable data were obtained. This included the lack of copy number change by both RT-qPCR and FISH for clone RP11-100C24, one of the most common known copy number variants, as well as confirmation of deletions for clones RP11-89M16 and RP5-1011O17.ConclusionWe have described 16 novel CNVs in 27 individuals. Further study of a small selection of CNVs indicated concordant and discordant array vs. FISH/RT-qPCR results. Although a large number of CNVs has been reported to date, quantification using independent methods and detailed cellular and/or molecular assessment has been performed on a very small number of CNVs. This information is, however, very much needed as it is currently common practice to consider CNVs reported in normal subjects as benign changes when detected in individuals affected with a variety of developmental disorders.

Novel case of del(17)(q23.1q23.3) further highlights a recognizable phenotype involving deletions of chromosome (17)(q21q24).

We report on a girl with a phenotype and developmental profile initially suggestive of Angelman syndrome. Subsequently she was shown to have an interstitial deletion of the long arm of chromosome 17; [del(17)(q23.1q23.3)], the smallest unique cytogenetic deletion in this region documented to date. These findings and those of 4 others from the literature, with overlapping deletions of 17q and breakpoints between 17q21-17q24, are reviewed and compared. Similar phenotypic findings include growth retardation, global developmental delay, and specific musculoskeletal and craniofacial anomalies. The size of the specific deletion, and the proximal and distal breakpoints at this region of chromosome 17q, appear to be important in determining morbidity from cardiac involvement and may affect the extent of developmental delay.

Systemic lupus erythematosus and other autoimmune disorders in children with Noonan syndrome.

Elena Lopez-Rangel, Peter N. Malleson, David S. Lirenman, Benjamin Roa, Joanna Wiszniewska, and M.E. Suzanne Lewis* Department of Medical Genetics, British Columbia’s Children’s and Women’s Health Center, University of British Columbia, British Columbia, Canada Division of Rheumatology, British Columbia’s Children’s and Women’s Hospital, University of British Columbia, British Columbia, Canada Department of Pediatrics, Division of Pediatric Nephrology, British Columbia’s Children’s and Women’s Hospital, University of British Columbia, British Columbia, Canada Department of Molecular and Human Genetics, Baylor DNA Diagnostic Laboratory, Baylor College of Medicine, Houston, Texas Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas Department of Medical Genetics, British Columbia’s Children’s and Women’s Health Center, University of British Columbia, British Columbia, Canada

Phenotype-Genotype Characterization of Alpha-Thalassemia Mental Retardation Syndrome Due to Isolated Monosomy of 16p13.3

An 8‐year‐old Caucasian girl presented with mild dysmorphic features and intellectual disability (ID) affecting multiple spheres. Dysmorphisms included a high forehead with up‐slanting palpebral fissures, prominent nasal root and bridge, flattened maxilla, high‐arched palate, and anterior frenulum. Structural brain anomalies included reduced periventricular white matter volume and thin corpus callosum. The presence of HbH bodies and her clinical presentation raised suspicion for autosomal alpha‐thalassemia mental retardation syndrome (ATR‐16). Whole‐genome array analysis at 1 Mb resolution was performed, which revealed a sub‐microscopic loss of 16p involving clones RP11‐344L6 at 0.1 Mb, RP1‐121I4 at 0.2 Mb and RP11‐334D3 at 1 Mb. FISH confirmed deletion (del) of the terminal clone (RP1‐121I4) on 16pter, which was de novo in origin. The more proximal clone RP11‐334D3 (at 1 Mb) showed diminished FISH signal intensity on one of the homologues, suggesting that one breakpoint occurred within this clone. Quantitative PCR (qPCR) confirmed a de novo deletion encompassing SOX8 (at 0.97 Mb). ATR‐16 is characterized by ID with mild, nonspecific dysmorphic features, and is associated with terminal del16p (MIM No. 141750). Cases of isolated monosomy for 16p are rarely described; such descriptions help to delineate the syndrome in the absence of confounding karyotypic anomalies. We describe detailed molecular cytogenetic and clinical findings relating to a subject with ATR‐16.