RESEARCH ARTICLE Spectrum of Elastin Sequence Variants and Cardiovascular Phenotypes in 49 Patients With Williams–Beuren Syndrome Maria Delio, 1 Kathleen Pope, 2 Tao Wang, 3 Joy Samanich, 2 Chad R. Haldeman-Englert, 4 Paige Kaplan, 5 Tamim H. Shaikh, 6 Jinlu Cai, 1 Robert W. Marion, 2 Bernice E. Morrow, 1 * and Melanie Babcock 1,7 1 Department of Genetics, Albert Einstein College of Medicine, Bronx, New York 2 The Center for Congenital Disorders, Department of Pediatrics, Montefiore Medical Center, Bronx, New York 3 Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, New York 4 Department of Pediatrics, Wake Forest University School of Medicine, Winston-Salem, North Carolnia 5 Department of Pediatrics, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania 6 Department of Pediatrics, University of Colorado Denver, Aurora, Colorado 7 Department of Genetics and Genomic Sciences, Mount Sinai School of Medicine, New York, New York Manuscript Received: 22 January 2012; Manuscript Accepted: 24 October 2012 Haploinsufficiency of the elastin gene (ELN) on 7q11.23 is responsible for supravalvular aortic stenosis (SVAS) and other arteriopathies in patients with Williams–Beuren syndrome (WBS). These defects occur with variable penetrance and expres- sivity, but the basis of this is unknown. To determine whether DNA variations in ELN could serve as genetic modifiers, we sequenced the 33 exons and immediately surrounding sequence of the ELN gene (9,455 bp of sequence) in 49 DNAs from patients with WBS and compared cardiovascular phenotypes. Four mis- sense, and four novel intronic variants were identified from a total of 24 mostly intronic single nucleotide variations and one indel. Two missense changes were present in one patient each, one published, p.Gly610Ser in exon 27 (MAF, 0.003) and one novel, p.Cys714Tyr, in exon 33 (MAF, 0.001), were rare in the general population. To identify a statistical association between the variants identified here and cardiovascular phenotypes a larger cohort would be needed. Ó 2013 Wiley Periodicals, Inc. Key words: Williams–Beuren syndrome; Elastin; DNA polymor- phisms; supravalvular aortic stenosis; bicuspid valve aorta INTRODUCTION Williams–Beuren syndrome (WBS; OMIM# 194050) is associated with a 1.55–1.84 Mb hemizygous 7q11.23 deletion that usually occurs de novo during meiosis. Cardiovascular anomalies occur in approximately 60–84% of WBS patients and include supra- valvular aortic stenosis (SVAS), pulmonary stenosis (PS), bicuspid aortic valve and other arteriopathies, ventricular septal defects (VSDs), and mitral valve abnormalities [Pober et al., 2008; Collins et al., 2010]. Cardiovascular abnormalities, particularly arterio- pathies, have a major impact on morbidity and mortality in WBS, and there is still much to learn about the basis of such defects. Significant evidence points to the elastin gene (ELN) as being responsible for arteriopathies and other cardiovascular defects occurring in association with WBS. Firstly, ELN is hemizygously deleted in patients with WBS [Ewart et al., 1993]. Second, ELN comprises 33 exons and encodes for tropoelastin, which is synthe- sized in smooth muscle cells and forms the major elastic component of the arterial extracellular matrix required for their elasticity [Indik et al., 1987; Fazio et al., 1988]. Additional evidence tying the ELN gene to the pathogenesis of arteriopathies was provided by a family with nonsyndromic SVAS with a disruption of the ELN due to a Additional supporting information may be found in the online version of this article. *Correspondence to: Bernice E. Morrow, Ph.D., Albert Einstein College of Medicine, 1300 Morris Park Avenue; Price 402, Bronx, NY 10461. E-mail: [email protected]Article first published online in Wiley Online Library (wileyonlinelibrary.com): 7 February 2013 DOI 10.1002/ajmg.a.35784 How to Cite this Article: Delio M, Pope K, Wang T, Samanich J, Haldeman-Englert CR, Kaplan P, Shaikh TH, Cai J, Marion RW, Morrow BE, Babcock M. 2013. Spectrum of elastin sequence variants and cardiovascular phenotypes in 49 patients with Williams–Beuren syndrome. Am J Med Genet Part A 161A:527–533. Ó 2013 Wiley Periodicals, Inc. 527
Transcript
RESEARCH ARTICLE
Spectrum of Elastin Sequence Variants andCardiovascular Phenotypes in 49 PatientsWith Williams–Beuren SyndromeMaria Delio,1 Kathleen Pope,2 Tao Wang,3 Joy Samanich,2 Chad R. Haldeman-Englert,4 Paige Kaplan,5
Tamim H. Shaikh,6 Jinlu Cai,1 Robert W. Marion,2 Bernice E. Morrow,1* and Melanie Babcock1,7
1Department of Genetics, Albert Einstein College of Medicine, Bronx, New York2The Center for Congenital Disorders, Department of Pediatrics, Montefiore Medical Center, Bronx, New York3Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, New York4Department of Pediatrics, Wake Forest University School of Medicine, Winston-Salem, North Carolnia5Department of Pediatrics, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania6Department of Pediatrics, University of Colorado Denver, Aurora, Colorado7Department of Genetics and Genomic Sciences, Mount Sinai School of Medicine, New York, New York
Manuscript Received: 22 January 2012; Manuscript Accepted: 24 October 2012
Haploinsufficiency of the elastin gene (ELN) on 7q11.23 is
responsible for supravalvular aortic stenosis (SVAS) and other
arteriopathies in patients with Williams–Beuren syndrome
(WBS). These defects occurwith variable penetrance and expres-
sivity, but the basis of this is unknown. To determine whether
DNA variations in ELN could serve as genetic modifiers, we
sequenced the 33 exons and immediately surrounding sequence
of the ELN gene (9,455 bp of sequence) in 49DNAs frompatients
with WBS and compared cardiovascular phenotypes. Four mis-
sense, and four novel intronic variants were identified from a
total of 24 mostly intronic single nucleotide variations and one
indel. Two missense changes were present in one patient each,
one published, p.Gly610Ser in exon 27 (MAF, 0.003) and one
novel, p.Cys714Tyr, in exon 33 (MAF, 0.001), were rare in the
general population. To identify a statistical association between
the variants identified here and cardiovascular phenotypes a
larger cohort would be needed. � 2013 Wiley Periodicals, Inc.
Of interest, the rs199469621 variant was not present in 410 individ-
uals that were sequenced as part of the 1,000 Genomes Project. It is
possible that this SNV results in a modification of the protein.
Though our studywas limited only to the ELN gene, it is possible
that DNA variations of genes elsewhere in the genome could alter
the cardiovascular phenotype in WBS patients. To identify such
causative genes, it would be necessary to perform a genome wide
association study (GWAS) in a much larger cohort of individuals
with WBS, on the order currently being done for other complex
traits [McCarthy et al., 2008]. A GWAS could find an association
between common SNP variants and presence or absence of SVAS.
Also, using whole genome sequencing to identify rare DNA
sequence variations could explain the basis of variable expressivity,
as it has for other complex traits, if these variationswere found to be
different within a cohort of the given phenotype and found to occur
in a unique cluster of genes with respect to each individual [Cirulli
and Goldstein, 2010]. Genes encoding proteins that interact with
tropoelastin, that are required for its extracellular modification, or
that interact with it in the extracellular space would be good
candidates to sequence. In addition to genetic factors, it is also
likely that environmental exposures could impact the severity of the
disorder. These may include maternal disease, such as diabetes or
hypertension. Finally, stochastic factors influencing these pheno-
types cannot be ruled out. This report offers an attempt to begin to
address the question starting with the causative gene, ELN.
ACKNOWLEDGMENTS
We thank all the patients and family members for participating in
this study.We also realize thatmany clinical support staff should be
thanked for significant effort to obtain informed consent and blood
or saliva specimens. We appreciated all the technical assistance
performed by Dr. Jidong Shan and Ms. Debbie Lewis in the
Molecular Cytogenetics Core at Einstein. We also thankMr. David
Reynolds and Limin Shan, as well as,Ms. Elsa Boschen for perform-
ing DNA purification and sequencing in the Genomics Core at
Einstein. We acknowledge the support of the Williams Syndrome
Center, the Division of Genetics, and the Department of Pediatrics
at the Children’s Hospital at Montefiore.
FIG. 1. Schematic representation of the 7q11.2 human elastin gene based on the reference sequence (NM_000501.2). Shaded boxes represent the
domain structure of the gene’s 33 exons (modified from [Tamburro et al., 2003]). Exon one includes the 50 translational start site. Found above theexons are missense SNPs and found below the exons are novel and synonymous SNPs. All novel SNPs are displayed with a (þ). The variant positionand base change are also noted. The box displays the chromatograms for the reference (left) and novel, missense variant (right) for rs1994621,
which is observed within the highly conserved C-terminus domain. The SNP is highlighted in black. [Color figure can be seen in the online version of
this article, available at http://wileyonlinelibrary.com/journal/ajmga]
532 AMERICAN JOURNAL OF MEDICAL GENETICS PART A
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