Cammon B. Arrington

Extra-embryonic syndecan 2 regulates organ primordia migration and fibrillogenesis throughout the zebrafish embryo.

One of the first steps in zebrafish heart and gut organogenesis is the migration of bilateral primordia to the midline to form cardiac and gut tubes. The mechanisms that regulate this process are poorly understood. Here we show that the proteoglycan syndecan 2 (Sdc2) expressed in the extra-embryonic yolk syncytial layer (YSL) acts locally at the YSL-embryo interface to direct organ primordia migration, and is required for fibronectin and laminin matrix assembly throughout the embryo. Surprisingly, neither endogenous nor exogenous sdc2 expressed in embryonic cells can compensate for knockdown of sdc2 in the YSL, indicating that Sdc2 expressed in extra-embryonic tissues is functionally distinct from Sdc2 in embryonic cells. The effects of sdc2 knockdown in the YSL can be rescued by extra-embryonic Sdc2 lacking an extracellular proteolytic cleavage (shedding) site, but not by extra-embryonic Sdc2 lacking extracellular glycosaminoglycan (GAG) addition sites, suggesting that distinct GAG chains on extra-embryonic Sdc2 regulate extracellular matrix assembly, cell migration and epithelial morphogenesis of multiple organ systems throughout the embryo.

Exome Analysis of a Family with Pleiotropic Congenital Heart Disease

Background— A number of single gene defects have been identified in patients with isolated or nonsyndromic congenital heart defects (CHDs). However, due to significant genetic heterogeneity, candidate gene approaches have had limited success in finding high-risk alleles in most cases. The purpose of this study was to use exome sequencing to identify high-risk gene variants in a family with highly penetrant pleiotropic CHD. Methods and Results— DNA samples from 2 members of a family with diverse CHD were analyzed by exome sequencing. Variants were filtered to eliminate common variants and sequencing artifacts and then prioritized based on the predicted effect of the variant and on gene function. The remainder of the family was screened using polymerase chain reaction, high-resolution melting analysis, and DNA sequencing to evaluate variant segregation. After filtering, >2000 rare variants (including single nucleotide substitutions and indels) were shared by the 2 individuals. Of these, 46 were nonsynonymous, 3 were predicted to alter splicing, and 6 resulted in a frameshift. Prioritization reduced the number of variants potentially involved in CHD to 18. None of the variants completely segregated with CHD in the kindred. However, 1 variant, Myh6 Ala290Pro, was identified in all but 1 affected individual. This variant was previously identified in a patient with tricuspid atresia and large secundum atrial septal defect. Conclusions— It is likely that next-generation sequencing will become the method of choice for unraveling the complex genetics of CHD, but information gained by analysis of transmission through families will be crucial.

Somatic mosaicism contributes to phenotypic variation in Timothy syndrome

Timothy syndrome type 1 (TS‐1) is a rare disorder that affects multiple organ systems and has a high incidence of sudden death due to profound QT prolongation and resultant ventricular arrhythmias. All previously described cases of TS‐1 are the result of a missense mutation in exon 8A (p.G406R), an alternatively spliced variant of the L‐type calcium channel gene (Cav1.2, CACNA1C). Most patients reported in the literature represent highly affected individuals who present early in life with severe cardiac and neurological manifestations. Here, we describe somatic mosaicism in TS‐1 patients with less severe manifestations than the typical TS‐1 patient. These findings suggest that the TS prognosis may not be as dismal as previously reported. Moreover, our findings have implications for genetic counseling in that previously described de novo TS mutations may represent cases of parental mosaicism and warrant careful genotyping of parental tissue other than peripheral blood lymphocytes.

Renin-Angiotensin-Aldosterone Genotype Influences Ventricular Remodeling in Infants With Single Ventricle

Background— We investigated the effect of polymorphisms in the renin-angiotensin-aldosterone system (RAAS) genes on ventricular remodeling, growth, renal function, and response to enalapril in infants with single ventricle. Methods and Results— Single ventricle infants enrolled in a randomized trial of enalapril were genotyped for polymorphisms in 5 genes: angiotensinogen, angiotensin-converting enzyme, angiotensin II type 1 receptor, aldosterone synthase, and chymase. Alleles associated with renin-angiotensin-aldosterone system upregulation were classified as risk alleles. Ventricular mass, volume, somatic growth, renal function using estimated glomerular filtration rate, and response to enalapril were compared between patients with ≥2 homozygous risk genotypes (high risk), and those with <2 homozygous risk genotypes (low risk) at 2 time points: before the superior cavopulmonary connection (pre-SCPC) and at age 14 months. Of 230 trial subjects, 154 were genotyped: Thirty-eight were high risk, and 116 were low risk. Ventricular mass and volume were elevated in both groups pre-SCPC. Ventricular mass and volume decreased and estimated glomerular filtration rate increased after SCPC in the low-risk (P<0.05), but not the high-risk group. These responses were independent of enalapril treatment. Weight and height z-scores were lower at baseline, and height remained lower in the high-risk group at 14 months, especially in those receiving enalapril (P<0.05). Conclusions— Renin-angiotensin-aldosterone system–upregulation genotypes were associated with failure of reverse remodeling after SCPC surgery, less improvement in renal function, and impaired somatic growth, the latter especially in patients receiving enalapril. Renin-angiotensin-aldosterone system genotype may identify a high-risk subgroup of single ventricle patients who fail to fully benefit from volume-unloading surgery. Follow-up is warranted to assess long-term impact. Clinical Trial Registration— http://www.clinicaltrials.gov. Unique identifier: NCT00113087.

Absence of TGFBR1 and TGFBR2 Mutations in Patients With Bicuspid Aortic Valve and Aortic Dilation

Mutations in the genes encoding transforming growth factor-beta receptor types I and II (TGFBR1 and TGFBR2, respectively) are commonly identified in patients with Loeys-Dietz syndrome, as well as some patients with Marfans syndrome or familial thoracic aortic aneurysms and dissections. This suggests that there is considerable phenotypic heterogeneity associated with mutations in these genes. Because bicuspid aortic valve (BAV) is a congenital heart defect in patients with Loeys-Dietz syndrome, this study was conducted to investigate whether variants in TGFBR1 or TGFBR2 are responsible for sporadic BAV. Analysis of these genes in 35 patients with BAVs identified only known single-nucleotide polymorphisms or novel synonymous or intronic substitutions. In conclusion, mutations in TGFBR1 and TGFBR2 rarely cause sporadic BAV.

Haploinsufficiency of the LIM domain containing preferred translocation partner in lipoma (LPP) gene in patients with tetralogy of Fallot and VACTERL association

Haploinsufficiency of the LIM Domain Containing Preferred Translocation Partner in Lipoma (LPP) Gene in Patients With Tetralogy of Fallot and VACTERL Association Cammon B. Arrington, Ankita Patel, Carlos A. Bacino, and Neil E. Bowles* Division of Cardiology, Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, Utah Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas

A Family-Based Paradigm to Identify Candidate Chromosomal Regions for Isolated Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a developmental defect of the diaphragm that causes high newborn mortality. Isolated or non‐syndromic CDH is considered a multifactorial disease, with strong evidence implicating genetic factors. As low heritability has been reported in isolated CDH, family‐based genetic methods have yet to identify the genetic factors associated with the defect. Using the Utah Population Database, we identified distantly related patients from several extended families with a high incidence of isolated CDH. Using high‐density genotyping, seven patients were analyzed by homozygosity exclusion rare allele mapping (HERAM) and phased haplotype sharing (HapShare), two methods we developed to map shared chromosome regions. Our patient cohort shared three regions not previously associated with CDH, that is, 2q11.2–q12.1, 4p13 and 7q11.2, and two regions previously involved in CDH, that is, 8p23.1 and 15q26.2. The latter regions contain GATA4 and NR2F2, two genes implicated in diaphragm formation in mice. Interestingly, three patients shared the 8p23.1 locus and one of them also harbored the 15q26.2 segment. No coding variants were identified in GATA4 or NR2F2, but a rare shared variant was found in intron 1 of GATA4. This work shows the role of heritability in isolated CDH. Our family‐based strategy uncovers new chromosomal regions possibly associated with disease, and suggests that non‐coding variants of GATA4 and NR2F2 may contribute to the development of isolated CDH. This approach could speed up the discovery of the genes and regulatory elements causing multifactorial diseases, such as isolated CDH.

Validation of association of the apolipoprotein E ε2 allele with neurodevelopmental dysfunction after cardiac surgery in neonates and infants.

OBJECTIVE Apolipoprotein E (APOE) genotype is a determinant of neurologic recovery after brain ischemia and traumatic brain injury. The APOE ε2 allele has been associated with worse neurodevelopmental (ND) outcome after repair of congenital heart defects (CHD) in infancy. Replication of this finding in an independent cohort is essential to validate the observed genotype-phenotype association. METHODS The association of APOE genotype with ND outcomes was assessed in a combined cohort of patients with single-ventricle CHD enrolled in the Single Ventricle Reconstruction and Infant Single Ventricle trials. ND outcome was assessed at 14 months using the Psychomotor Development Index (PDI) and Mental Development Index (MDI) of the Bayley Scales of Infant Development-II. Stepwise multivariable regression was performed to develop predictive models for PDI and MDI scores. RESULTS Complete data were available for 298 of 435 patients. After adjustment for preoperative and postoperative covariates, the APOE ε2 allele was associated with a lower PDI score (P = .038). Patients with the ε2 allele had a PDI score approximately 6 points lower than those without the risk allele, explaining 1.04% of overall PDI variance, because the ε2 allele was present in only 11% of the patients. There was a marginal effect of the ε2 allele on MDI scores (P = .058). CONCLUSIONS These data validate the association of the APOE ε2 allele with adverse early ND outcomes after cardiac surgery in infants, independent of patient and operative factors. Genetic variants that decrease neuroresilience and impair neuronal repair after brain injury are important risk factors for ND dysfunction after surgery for CHD.

Patent Foramen Ovale in Children with Migraine Headaches

OBJECTIVE To determine the prevalence of patent foramen ovale (PFO) in children with migraine. STUDY DESIGN Children aged 6.0 to 18.0 years with migraine headache were evaluated for PFO and right-to-left shunting with color-flow Doppler scanning, saline solution contrast transthoracic echocardiography, and contrast transcranial Doppler scanning. RESULTS The population consisted of 109 children with migraine; 38 (35%) with aura and 71 (65%) without aura. The overall PFO prevalence was 35%, similar to the general population (35% vs 25%; P = .13). However, compared with the general population (25%), the PFO prevalence was significantly greater in subjects with aura (50%, P = .0004) but similar in those without aura (27%, P = .73). Atrial shunt size was not associated with the presence or absence of aura. CONCLUSION Children with migraine with aura have a significantly higher prevalence of PFO compared with those without aura or the general population. These data suggest that PFO may contribute to the pathogenesis of migraine with aura in children and have implications for clinical decision making.

Interstitial deletion 8q11.2-q13 with congenital anomalies of CHARGE association

Specific genetic loci responsible for CHARGE association are currently unknown. Herein, we describe a neonate with clinical manifestations consistent with CHARGE association who has a de novo interstitial deletion involving bands 8q11.2 to 8q13. Genetic mapping and genomic microarray technology have been used to more accurately define the breakpoints of this deletion. Within the deleted region, there are approximately 150 expressed genes, one or more of which may contribute to the manifestations of CHARGE association.