Multiple regions within 8q24 independently affect risk for prostate cancer

After the recent discovery that common genetic variation in 8q24 influences inherited risk of prostate cancer, we genotyped 2,973 SNPs in up to 7,518 men with and without prostate cancer from five populations. We identified seven risk variants, five of them previously undescribed, spanning 430 kb and each independently predicting risk for prostate cancer (P = 7.9 x 10(-19) for the strongest association, and P < 1.5 x 10(-4) for five of the variants, after controlling for each of the others). The variants define common genotypes that span a more than fivefold range of susceptibility to cancer in some populations. None of the prostate cancer risk variants aligns to a known gene or alters the coding sequence of an encoded protein.

De novo copy number variants identify new genes and loci in isolated sporadic tetralogy of Fallot

Tetralogy of Fallot (TOF), the most common severe congenital heart malformation, occurs sporadically, without other anomaly, and from unknown cause in 70% of cases. A genome-wide survey of 114 TOF patients and their unaffected parents identified 11 de novo copy number variants (CNVs) that were absent or extremely rare (<0.1%) in 2,265 controls. A second, independent TOF cohort (n = 398) was then examined for additional CNVs at these loci. In 1% (5/512, p = 0.0002, OR = 22.3) of non-syndromic sporadic TOF cases we identified CNVs at chromosome 1q21.1. Recurrent CNVs were also identified at 3p25.1, 7p21.3 and 22q11.2. CNVs in a single TOF case occurred at six loci, two that encode known (NOTCH1, JAG1) disease genes. Our data predicts that at least 10% (4.5–15.5, 95% CI) of sporadic, non-syndromic TOF reflects de novo CNVs and implicates mutations within these loci as etiologic in other cases of TOF.

Polony Multiplex Analysis of Gene Expression (PMAGE) in Mouse Hypertrophic Cardiomyopathy

We describe a sensitive mRNA profiling technology, PMAGE (for "polony multiplex analysis of gene expression"), which detects messenger RNAs (mRNAs) as rare as one transcript per three cells. PMAGE incorporates an improved ligation-based method to sequence 14-nucleotide tags derived from individual mRNA molecules. One sequence tag from each mRNA molecule is amplified onto a separate 1-micrometer bead, denoted as a polymerase colony or polony, and about 5 million polonies are arrayed in a flow cell for parallel sequencing. Using PMAGE, we identified early transcriptional changes that preceded pathological manifestations of hypertrophic cardiomyopathy in mice carrying a disease-causing mutation. PMAGE provided a comprehensive profile of cardiac mRNAs, including low-abundance mRNAs encoding signaling molecules and transcription factors that are likely to participate in disease pathogenesis.

Presentation, diagnosis, and medical management of heart failure in children: Canadian Cardiovascular Society guidelines

Pediatric heart failure (HF) is an important cause of morbidity and mortality in childhood. This article presents guidelines for the recognition, diagnosis, and early medical management of HF in infancy, childhood, and adolescence. The guidelines are intended to assist practitioners in office-based or emergency room practice, who encounter children with undiagnosed heart disease and symptoms of possible HF, rather than those who have already received surgical palliation. The guidelines have been developed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology, and are accompanied by practical Recommendations for their application in the clinical setting, supplemented by online material. This work does not include Recommendations for advanced management involving ventricular assist devices, or other device therapies.

Genetic and environmental risk factors in congenital heart disease functionally converge in protein networks driving heart development

Congenital heart disease (CHD) occurs in ∼1% of newborns. CHD arises from many distinct etiologies, ranging from genetic or genomic variation to exposure to teratogens, which elicit diverse cell and molecular responses during cardiac development. To systematically explore the relationships between CHD risk factors and responses, we compiled and integrated comprehensive datasets from studies of CHD in humans and model organisms. We examined two alternative models of potential functional relationships between genes in these datasets: direct convergence, in which CHD risk factors significantly and directly impact the same genes and molecules and functional convergence, in which risk factors significantly impact different molecules that participate in a discrete heart development network. We observed no evidence for direct convergence. In contrast, we show that CHD risk factors functionally converge in protein networks driving the development of specific anatomical structures (e.g., outflow tract, ventricular septum, and atrial septum) that are malformed by CHD. This integrative analysis of CHD risk factors and responses suggests a complex pattern of functional interactions between genomic variation and environmental exposures that modulate critical biological systems during heart development.

S100A4/Mts1 produces murine pulmonary artery changes resembling plexogenic arteriopathy and is increased in human plexogenic arteriopathy

S100A4/Mts1 confers a metastatic phenotype in tumor cells and may also be related to resistance to apoptosis and angiogenesis. Approximately 5% of transgenic mice overexpressing S100A4/Mts1 develop pulmonary arterial changes resembling human plexogenic arteriopathy with intimal hyperplasia leading to occlusion of the arterial lumen. To assess the pathophysiological significance of this observation, immunohistochemistry was applied to quantitatively analyze S100A4/Mts1 expression in pulmonary arteries in surgical lung biopsies from children with pulmonary hypertension secondary to congenital heart disease. S100A4/Mts1 was not detected in pulmonary arteries with low-grade hypertensive lesions but was expressed in smooth muscle cells of lesions showing neointimal formation and with increased intensity in vessels with an occlusive neointima and plexiform lesions. Putative downstream targets of S100A4/Mts1 include Bax, which is pro-apoptotic, and the pro-angiogenic vascular endothelial growth factor (VEGF). The increase in S100A4/Mts1 expression precedes heightened expression of Bax in progressively severe neointimal lesions but in non-S100A4/Mts1-expressing cells. VEGF immunoreactivity did not correlate with severity of disease. The relationship of increased S100A4/Mts1 to pathologically similar lesions in the transgenic mice and patients occurs despite differences in localization (endothelial versus smooth muscle cells).

C-Met expression and mechanical activation of satellite cells on cultured muscle fibers

Single-fiber cultures can be used to model satellite cell activation in vivo. Although technical deficiencies previously prevented study of stretch-induced events, here we describe a method developed to study satellite cell gene expression by in situ hybridization (ISH) using protocol modifications for fiber adhesion and fixation. The hypothesis that mechanical stretching activates satellite cells was tested. Fiber cultures were established from normal flexor digitorum brevis muscles and plated on FlexCell dishes with a layer of Vitrogen. After 2 hr of stretch in the presence of BrdU, satellite cells on fibers attached to Vitrogen were activated above control levels. In the absence of activating treatments or mechanical stretch, ISH studies showed 0-6 c-Met+ satellite cells per fiber. Time course experiments demonstrated stable quiescence in the absence of stretch and significant peaks in activation after 30 min and 2 hr of stretch. Frequency distributions for unstretched fiber cultures showed a significantly greater number of quiescent c-Met+ satellite cells than were activated by stretching, suggesting that typical activation stimuli did not trigger cycling in the entire c-Met+ population of satellite cells. These methods have a strong potential to further dissect the nature of stretch-induced activation and gene expression among characterized populations of individual quiescent and activated satellite cells.

Current methods for the maturation of induced pluripotent stem cell-derived cardiomyocytes

Induced pluripotent stem cells (iPSCs) were first generated by Yamanaka and colleagues over a decade ago. Since then, iPSCs have been successfully differentiated into many distinct cell types, enabling tissue-, disease-, and patient-specific in vitro modelling. Cardiovascular disease is the greatest cause of mortality worldwide but encompasses rarer disorders of conduction and myocardial function for which a cellular model of study is ideal. Although methods to differentiate iPSCs into beating cardiomyocytes (iPSC-CMs) have recently been adequately optimized and commercialized, the resulting cells remain largely immature with regards to their structure and function, demonstrating fetal gene expression, disorganized morphology, reliance on predominantly glycolytic metabolism and contractile characteristics that differ from those of adult cardiomyocytes. As such, disease modelling using iPSC-CMs may be inaccurate and of limited utility. However, this limitation is widely recognized, and numerous groups have made substantial progress in addressing this problem. This review highlights successful methods that have been developed for the maturation of human iPSC-CMs using small molecules, environmental manipulation and 3-dimensional (3D) growth approaches.

Brazilian urban population genetic structure reveals a high degree of admixture

Advances in genotyping technologies have contributed to a better understanding of human population genetic structure and improved the analysis of association studies. To analyze patterns of human genetic variation in Brazil, we used SNP data from 1129 individuals--138 from the urban population of Sao Paulo, Brazil, and 991 from 11 populations of the HapMap Project. Principal components analysis was performed on the SNPs common to these populations, to identify the composition and the number of SNPs needed to capture the genetic variation of them. Both admixture and local ancestry inference were performed in individuals of the Brazilian sample. Individuals from the Brazilian sample fell between Europeans, Mexicans, and Africans. Brazilians are suggested to have the highest internal genetic variation of sampled populations. Our results indicate, as expected, that the Brazilian sample analyzed descend from Amerindians, African, and/or European ancestors, but intermarriage between individuals of different ethnic origin had an important role in generating the broad genetic variation observed in the present-day population. The data support the notion that the Brazilian population, due to its high degree of admixture, can provide a valuable resource for strategies aiming at using admixture as a tool for mapping complex traits in humans.

Dissecting spatio-temporal protein networks driving human heart development and related disorders

Aberrant organ development is associated with a wide spectrum of disorders, from schizophrenia to congenital heart disease, but systems-level insight into the underlying processes is very limited. Using heart morphogenesis as general model for dissecting the functional architecture of organ development, we combined detailed phenotype information from deleterious mutations in 255 genes with high-confidence experimental interactome data, and coupled the results to thorough experimental validation. Hereby, we made the first systematic analysis of spatio-temporal protein networks driving many stages of a developing organ identifying several novel signaling modules. Our results show that organ development relies on surprisingly few, extensively recycled, protein modules that integrate into complex higher-order networks. This design allows the formation of a complicated organ using simple building blocks, and suggests how mutations in the same genes can lead to diverse phenotypes. We observe a striking temporal correlation between organ complexity and the number of discrete functional modules coordinating morphogenesis. Our analysis elucidates the organization and composition of spatio-temporal protein networks that drive the formation of organs, which in the future may lay the foundation of novel approaches in treatments, diagnostics, and regenerative medicine.

The impact of epigenetics on cardiovascular disease

Mortality and morbidity from cardiovascular diseases (CVDs) represents a huge burden to society. It is recognized that environmental factors and individual lifestyles play important roles in disease susceptibility, but the link between these external risk factors and our genetics has been unclear. However, the discovery of sequence-independent heritable DNA changes (epigenetics) have helped us to explain the link between genes and the environment. Multiple diverse epigenetic processes, including DNA methylation, histone modification, and the expression of non-coding RNA molecules affect the expression of genes that produce important changes in cellular differentiation and function, influencing the health and adaptability of the organism. CVDs such as congenital heart disease, cardiomyopathy, heart failure, cardiac fibrosis, hypertension, and atherosclerosis are now being viewed as much more complex and dynamic disorders. The role of epigenetics in these and other CVDs is currently under intense scrutiny, and we can expect important insights to emerge, including novel biomarkers and new approaches to enable precision medicine. This review summarizes the recent advances in our understanding of the role of epigenetics in CVD.

Vancomycin relieves mycophenolate mofetil-induced gastrointestinal toxicity by eliminating gut bacterial β-glucuronidase activity

Mycophenolate mofetil (MMF) is commonly prescribed and has proven advantages over other immunosuppressive drugs. However, frequent gastrointestinal side effects through an unknown mechanism limit its use. We have found that consumption of MMF alters the composition of the gut microbiota, selecting for bacteria expressing the enzyme β-glucuronidase (GUS) and leading to an up-regulation of GUS activity in the gut of mice and symptomatic humans. In the mouse, vancomycin eliminated GUS-expressing bacteria and prevented MMF-induced weight loss and colonic inflammation. Our work provides a mechanism for the toxicity associated with MMF and a future direction for the development of therapeutics.

An intact microbiota is required for the gastrointestinal toxicity of the immunosuppressant mycophenolate mofetil

BACKGROUND

Mycophenolate mofetil (MMF) is commonly prescribed after transplantation and has major advantages over other immunosuppressive drugs, but frequent gastrointestinal (GI) side-effects limit its use. The mechanism(s) underlying MMF-related GI toxicity have yet to be elucidated.

METHODS

To investigate MMF-related GI toxicity, experimental mice were fed chow containing MMF (0.563%) and multiple indices of toxicity, including weight loss and colonic inflammation, were measured. Changes in intestinal microbial composition were detected using 16S rRNA Illumina sequencing, and downstream PICRUSt analysis was used to predict metagenomic pathways involved. Germ-free (GF) mice and mice treated with orally administered broad-spectrum antibiotics (ABX) were utilized to interrogate the importance of the microbiota in MMF-induced GI toxicity.

RESULTS

Mice treated with MMF exhibited significant weight loss, related to loss of body fat and muscle, and marked colonic inflammation. MMF exposure was associated with changes in gut microbial composition, as demonstrated by a loss of overall diversity, expansion of Proteobacteria (specifically Escherichia/Shigella), and enrichment of genes involved in lipopolysaccharide (LPS) biosynthesis, which paralleled increased levels of LPS in the feces and serum. MMF-related GI toxicity was dependent on the intestinal microbiota, as MMF did not induce weight loss or colonic inflammation in GF mice. Furthermore, ABX prevented and reversed MMF-induced weight loss and colonic inflammation.

CONCLUSIONS

An intact intestinal microbiota is required to initiate and sustain the GI toxicity of MMF. MMF treatment causes dynamic changes in the composition of the intestinal microbiota that may be a targetable driver of the GI side-effects of MMF.

Activation of mitogen-activated protein kinases during natural freezing and thawing in the wood frog

The responses of mitogen-activated protein kinase (MAPK) family members, including ERK (extracellular signal-regulated kinase), JNK (c-Jun NH2-terminal kinase), and p38, in the metabolic responses to whole animal freezing (up to 24 h frozen at -2.5 degrees C) and thawing (up to 4 h at 5 degrees C after a 12 h freeze) were examined in four organs (liver, kidney, heart, brain) of the freeze-tolerant wood frog Rana sylvatica. Levels of the active phosphorylated form of p38 increased within 20 min as an early response to freezing in liver and kidney but rose later (after 12 h) in heart. Both JNK and p38 were activated during thawing in liver, kidney and heart with temporally-distinct patterns in each organ. The only MAPK response to freeze/thaw in frog brain was a transient elevation of p38 after 90 min thawing. ERK activity did not respond to freeze/thaw in any organ. The levels of c-Fos increased during freezing in kidney and brain whereas c-Jun was unaffected by freeze/thaw. Organ-specific responses by MAPKs, particularly p38, suggest that these may have roles in regulating metabolic or gene expression responses that may be adaptive in dealing with freezing stress or metabolic recovery during thawing.

Expression of ryanodine receptors in human embryonic kidney (HEK293) cells

It has been shown previously that mobilization of caffeine-sensitive intracellular calcium (Ca2+i) stores increased the release of amyloid beta-peptide (Abeta) from transfected human embryonic kidney cells (HEK293) [Querfurth, Jiang, Geiger and Selkoe (1997) J. Neurochem. 69, 1580-1591]. The present study was to test the hypothesis that the caffeine/Abeta responses were due to interactions with specific subtypes of ryanodine receptors (RyR) using [3H]ryanodine receptor binding, epifluorescence imaging of Ca2+i, immunocytofluorescence, immunoprecipitation and PCR techniques. [3H]Ryanodine bound to a single class of high-affinity caffeine-sensitive sites (Kd=9.9+/-1.6 nM, Bmax=25+/-4 fmol/mg of protein). RyRs were immuno-decorated in a punctate reticulo-linear pattern. Results from SDS/PAGE and reverse transcriptase-PCR demonstrated endogenous expression of type 1 (skeletal) and type 2 (cardiac) RyRs. HEK293 cell RyRs were functionally active, because (i) [Ca2+]i increased 2.8-fold over baseline following applications of 5-15 mM caffeine, (ii) repetitive spiked increases in [Ca2+]i were observed, and (iii) evidence for a use-dependent block was obtained. Some of these findings were extended to include HeLa and human fibroblast cell lines, suggesting a broader applicability to cells of epithelioid lineage. Implications for the processing of the beta-amyloid precursor protein in Alzheimer's disease and for calcium channel research using transfected HEK293 cells are discussed.

Mitogen-activated protein kinases and anoxia tolerance in turtles

The response of two vertebrate mitogen-activated protein kinase (MAPK) family members, the extracellular signal-regulated kinases (ERKs) and c-Jun NH2-terminal kinases (JNKs), to anoxia exposure in vivo was examined in organs (liver, heart, kidney, brain, spleen) of the anoxia-tolerant adult turtle, Trachemys scripta elegans. ERKs activities rose during anoxia only in spleen (a 2.8-fold increase). JNK activity showed a significant increase only in liver (4-fold increase) after 5 hr of anoxic submergence but declined thereafter. Levels of the transcription factor c-Fos were strongly suppressed in liver, heart, and kidney of anoxia-exposed turtles, whereas levels increased 2-fold in anoxic brain. The effect of anoxia on c-Myc was organ-specific and variable with 2- and 1.5-fold increases in protein expression in kidney and brain, respectively, and a 60% decrease in anoxic spleen. These results for an anoxia-tolerant animal suggest the potential importance of the MAPKs and of the immediate-early genes (c-fos, c-myc) in mediating adaptive responses to oxygen deprivation.

THSD1 (Thrombospondin Type 1 Domain Containing Protein 1) Mutation in the Pathogenesis of Intracranial Aneurysm and Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE

A ruptured intracranial aneurysm (IA) is the leading cause of a subarachnoid hemorrhage. This study seeks to define a specific gene whose mutation leads to disease.

METHODS

More than 500 IA probands and 100 affected families were enrolled and clinically characterized. Whole exome sequencing was performed on a large family, revealing a segregating THSD1 (thrombospondin type 1 domain containing protein 1) mutation. THSD1 was sequenced in other probands and controls. Thsd1 loss-of-function studies in zebrafish and mice were used for in vivo analyses and functional studies performed using an in vitro endothelial cell model.

RESULTS

A nonsense mutation in THSD1 was identified that segregated with the 9 affected (3 suffered subarachnoid hemorrhage and 6 had unruptured IA) and was absent in 13 unaffected family members (LOD score 4.69). Targeted THSD1 sequencing identified mutations in 8 of 507 unrelated IA probands, including 3 who had suffered subarachnoid hemorrhage (1.6% [95% confidence interval, 0.8%-3.1%]). These THSD1 mutations/rare variants were highly enriched in our IA patient cohort relative to 89 040 chromosomes in Exome Aggregation Consortium (ExAC) database (P<0.0001). In zebrafish and mice, Thsd1 loss-of-function caused cerebral bleeding (which localized to the subarachnoid space in mice) and increased mortality. Mechanistically, THSD1 loss impaired endothelial cell focal adhesion to the basement membrane. These adhesion defects could be rescued by expression of wild-type THSD1 but not THSD1 mutants identified in IA patients.

CONCLUSIONS

This report identifies THSD1 mutations in familial and sporadic IA patients and shows that THSD1 loss results in cerebral bleeding in 2 animal models. This finding provides new insight into IA and subarachnoid hemorrhage pathogenesis and provides new understanding of THSD1 function, which includes endothelial cell to extracellular matrix adhesion.

Non-invasive Investigations for the Diagnosis of Fontan-Associated Liver Disease in Pediatric and Adult Fontan Patients

Fontan-associated liver disease (FALD) is a serious complication related to the chronically elevated venous pressure and low cardiac output of this abnormal circulation. However, diagnostic markers for this condition are limited. We hypothesized that specific tests for fibrosis developed for other chronic liver diseases would identify a higher prevalence of FALD than ultrasound and standard laboratory tests and that identified abnormalities would correlate with time post-Fontan. In this cross-sectional study, we assessed 19 children (average age 8.4 ± 4.3 and 5.4 ± 4.1 years post-Fontan) and 8 adults (average age 31.5 ± 8.9 and 21.1 ± 4 years post-Fontan) using standard serum laboratory investigations assessing hepatic integrity and function, the FibroTest, liver ultrasound, and transient elastography (FibroScan). In adult Fontan patients, hemoglobin, C-reactive protein, and gamma-glutamyl transpeptidase were significantly increased, and white blood cell and platelet counts were significantly decreased in comparison to the pediatric cohort. International normalized ratio was mildly elevated in both children and adults. FibroTest results were suggestive of fibrosis regardless of time post-Fontan. FibroScan measurements were significantly correlated with time post-Fontan, but the incidence of ultrasound-detected liver abnormalities was variable. No cases of hepatocellular carcinoma were identified. Abnormalities suggestive of FALD occur in both children and adults post-Fontan. Select laboratory tests, and possibly ultrasound and FibroScan in some patients, appear to have the most promise for the non-invasive detection of FALD.

Effects of nitrobenzylthioinosine on neuronal injury, adenosine levels, and adenosine receptor activity in rat forebrain ischemia

Adenosine levels increase in brain during cerebral ischemia, and adenosine has receptor-mediated neuroprotective effects. This study was performed to test the hypothesis that nitrobenzylthioinosine (NBMPR), a selective and potent inhibitor of one adenosine transporter subtype termed ENT1, or es, can protect against ischemic neuronal injury by enhancing adenosine levels and potentiating adenosine receptor-mediated effects, including attenuation of the cellular production and release of tumor necrosis factor-alpha (TNF-alpha). In rats, the phosphorylated prodrug form of NBMPR, NBMPR-phosphate, or saline was administered by intracerebroventricular injection 30 min before forebrain ischemia. Seven days following the ischemic episode, rats were killed, and neuronal damage in the CA1 region of the hippocampus was assessed. The number of pyramidal neurons was significantly (p < 0.001) greater in the NBMPR-P treatment group. A trend toward protection was still evident at 28 days postreperfusion. Adenosine increased significantly during ischemia to levels eight- to 85-fold above basal. NBMPR-P treatment did not cause statistically significant increases in ischemic adenosine levels; however, this treatment tended to increase adenosine levels in all brain regions at 7 min postreperfusion. Ischemia-induced expression of TNF-alpha was not altered by NBMPR-P treatment, and the nonselective adenosine receptor antagonist 8-(p-sulfophenyl) theophylline did not abolish the neuroprotective effects of NBMPR-P treatment. These data indicate that NBMPR can protect CA1 pyramidal neurons from ischemic death without statistically significant effects on adenosine levels or adenosine receptor-mediated inhibition of the proinflammatory cytokine TNF-alpha.

Seasonal change and prolonged anoxia affect the kinetic properties of phosphofructokinase and pyruvate kinase in oysters

The effects of seasonal change, November versus July, and prolonged anoxia (96 h under N2 gas) on the properties of phosphofructokinase and pyruvate kinase from five tissues (gill, mantle, hepatopancreas, phasic adductor, catch adductor) of the oyster, Crassostrea virginica were investigated. Both enzymes showed tissue-specific and season-specific changes in kinetic properties; for pyruvate kinase this correlated with seasonal differences in enzyme elution patterns on hydroxylapatite chromatography. Kinetic properties of both enzymes in winter were consistent with primarily catabolic roles in glycolysis with responsiveness to cellular energy demands, whereas in summer these enzymes may be more closely regulated with respect to the biosynthetic and gluconeogenic functions of the tissues. Anoxia-induced changes in phosphofructokinase properties were relatively minor but anoxia stimulated changes in pyruvate kinase properties and elution profiles on hydroxylapatite in all tissues except mantle, with much greater effects seen for the enzyme from winter versus summer animals. For example, anoxia-induced changes in pyruvate kinase from winter gill included a fourfold rise in the substrate affinity constant for phosphoenolpyruvate, a sevenfold increase in the concentration of fructose-1,6-bisphosphate needed to activate the enzyme by 50%, and a 50% decrease in the concentration of L-alanine that inhibits activity by 50%. Changes in pyruvate kinase kinetics and hydroxylapatite elution patterns during prolonged anoxia are consistent with covalent modification of pyruvate kinase but contrary to results for many other mollusc species, anoxia exposure appears to induce a dephosphorylation of the enzyme.

Differential regulation of the mitochondrial ADP/ATP translocase gene in wood frogs under freezing stress

The gene Aat coding for ADP/ATP translocase (AAT) was cloned from liver of the freeze-tolerant wood frog, Rana sylvatica, via differential screening of a cDNA library from liver of frozen frogs and using probes from control versus frozen frogs. Sequence analysis showed that clone pBfFR07 bearing the AAT cDNA contained a 1318-bp insert with one full-length open reading frame. The deduced amino acid sequence included 317 residues, with 81-86% identities to mammalian AAT. A 1750-nt transcript from the Aat gene was detected using pBfFR07 probe and a putative frog AAT of over 30 kDa was visualized by immunoblotting using a polyclonal antibody raised against chicken AAT. Analysis of liver samples from a time course of freezing showed a maximal 4.5-fold increase in mRNA after 8 h with AAT protein peaking in 24-h frozen frogs. Freezing also induced Aat expression in bladder and lung. In liver, mRNA expression also responded positively to anoxia stress but not to experimental dehydration of the animals. These results suggest that AAT induction during freezing may be stimulated by the ischemia that develops when plasma freezes; changes in AAT may contribute to stabilizing energetics in mitochondrial versus cytosolic pools over freeze/thaw cycles.

Exome sequencing identifies a novel variant in ACTC1 associated with familial atrial septal defect

BACKGROUND

The genetics of congenital heart disease (CHD) remain incompletely understood. Exome sequencing has been successfully used to identify disease-causing mutations in familial disorders in which candidate gene analyses and linkage mapping have failed.

METHODS

We studied a large family characterized by autosomal dominant isolated secundum atrial septal defect (ASD) (MIM No. 612794). Candidate gene resequencing and linkage analysis were uninformative.

RESULTS

Whole-exome sequencing of 2 affected family members identified 44 rare shared variants, including a nonsynonymous mutation (c.532A>T, p.M178L, NM_005159.4) in alpha-cardiac actin (ACTC1). This mutation was absent from 1834 internal controls as well as from the 1000 Genomes and the Exome Sequencing Project (ESP) databases, but predictions regarding its effect on protein function were divergent. However, p.M178L was the only rare mutation segregating with disease in our family.

CONCLUSIONS

Our results provide further evidence supporting a causative role for ACTC1 mutations in ASD. Massively parallel sequencing of the exome allows for the detection of novel rare variants causing CHD without the limitations of a candidate gene approach. When mutation prediction algorithms are not helpful, studies of familial disease can help distinguish rare pathologic mutations from benign variants. Consideration of the family history can lead to genetic insights into CHD.