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(Circulation. 1995;91:1326-1329.)
© 1995 American Heart Association, Inc.
Articles |
Genetic Heterogeneity of Heart-Hand Syndromes
From the Departments of Medicine–Cardiovascular Division (C.T.B., S.D.S., C.E.S.), Radiology (B.W.), and Howard Hughes Medical Institute (C.E.S.) at Brigham and Women's Hospital, Boston, Mass; Department of Genetics (C.A.M.) and Howard Hughes Medical Institute (J.G.S.) at Harvard Medical School, Boston, Mass; Department of Radiology (A.K.P.), Children's Memorial Hospital, Chicago, Ill; Unidad de Genetica (F.P., S.R.F.), Hospital Universitario "La Fe," Valencia, Spain; Division of Cardiology (W.E.P.), Harrisburg Hospital, Harrisburg, Pa; Department of Pediatrics (S.E.L.), University of the Witwatersrand Medical School, Parktown, Republic of South Africa; and Genetics and Teratology Unit (L.H.), Children's Service, Massachusetts General Hospital, Boston, Mass.
Correspondence to Christine Seidman, MD, Department of Genetics, Harvard Medical School Alpert Bldg, Room 533, 200 Longwood Ave, Boston, MA 02115.
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Abstract |
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 Top Abstract IntroductionMethods Results Discussion References |
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Background Heart-hand syndromes compose a class of combined congenital cardiac and limb deformities. The prototypical heart-hand disorder is Holt-Oram syndrome, which is characterized by cardiac septation defects and radial ray limb deformity. We have recently mapped the Holt-Oram syndrome gene defect to the long arm of human chromosome 12 in two families. The role of this disease locus in the pathogenesis of related conditions such as heart-hand syndrome type III (cardiac conduction disease accompanied by skeletal malformations) or familial atrial septal defects is unknown.
Methods and Results Clinical evaluations and genetic linkage analyses were performed in five additional kindreds with Holt-Oram syndrome and also in one kindred with heart-hand syndrome type III and one kindred with familial atrial septal defect and conduction disease. Holt-Oram syndrome in all five kindreds mapped to chromosome 12q2. These studies and previous data provide odds of greater than 1025:1 that the Holt-Oram syndrome disease gene is at chromosome 12q2. In contrast, neither the phenotypically similar disorder heart-hand syndrome type III nor the locus responsible for a familial atrial septal defect with atrioventricular block maps to chromosome 12q2.
Conclusions We demonstrate that heart-hand syndromes are genetically heterogeneous. Conditions that clinically appear to be partial phenocopies of Holt-Oram syndrome arise from distinct disease genes.
Key Words: Holt-Oram syndrome • congenital heart defects • septal defects
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Introduction |
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TopAbstractIntroductionMethods Results Discussion References |
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Congenital cardiac and upper-limb malformations frequently occur in association and are classified as heart-hand syndromes. Despite multiple similarities in the clinical presentations of these syndromes, it remains unknown whether hereditary heart-hand syndromes arise from common or distinct genetic defects. A variety of morphological and anatomic criteria have led others to postulate that congenital heart diseases arise from a limited number of shared genetic defects.1 2 Elucidation of the genetic etiologies of these autosomal dominant heart-hand syndromes will improve diagnosis and management of a complex group of disorders with highly variable phenotypic expression.
The most common heart-hand syndrome is the Holt-Oram syndrome3 (MIM No. 142900). Diagnosis is based on skeletal preaxial radial ray abnormalities that may be unilateral and asymmetrical and can vary from subtle, subclinical findings to frank phocomelia. More than 85% of affected individuals also have cardiac malformations that typically include atrial and/or ventricular septal defects and atrioventricular nodal disease. The rare Heart-Hand syndrome Type II (Tabatznik's syndrome)4 5 has no known etiology and is characterized by upper-limb abnormalities (hypoplastic deltoids; skeletal anomalies in the humeri, radii, ulnae, and thenar bones; and brachydactyly type D) and congenital cardiac arrhythmias (junctional rhythms and atrial fibrillation). The poorly understood Heart-Hand syndrome Type III3 6 (MIM No. 140450) is phenotypically similar and is characterized by cardiac conduction disease (intraventricular delays and sick sinus syndrome). Skeletal malformations are limited to the hands and feet (brachydactyly type C). Septal defects have not yet been identified in patients with Heart-Hand syndrome Type III. Clinical similarities also exist between the heart-hand syndromes and a variety of other less complex autosomal dominant "partial phenocopy" conditions, including familial atrial septal defects (ASDs) with conduction disease3 7 (MIM No. 108900) that occur without limb deformities, and familial limb malformations that occur without cardiac defects.
Identification of the chromosomal location for a disease gene permits studies to ascertain whether phenotypically similar disorders are genetically related. We have previously demonstrated that a disease locus responsible for Holt-Oram syndrome in two families maps to human chromosome 12q2.8 Analyses of five additional families reported here demonstrate that the same genetic locus causes Holt-Oram syndrome in more than 60 affected individuals. To determine if the cardiac and/or limb abnormalities found in other heart-hand syndromes or in partial phenocopy syndromes are also due to a gene defect on chromosome 12q2, we have applied genetic linkage analysis to kindreds affected by Heart-Hand syndrome Type III or familial ASD with conduction disease. (The small size of families with Heart-Hand syndrome Type II/Tabatznik's syndrome precludes informative linkage analyses for this disorder.) We demonstrate that heart-hand syndromes are genetically heterogeneous, and partial phenocopy disorders arise from mutations at genomic loci distinct from that which causes Holt-Oram syndrome.
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Methods |
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TopAbstractIntroductionMethods Results Discussion References |
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Clinical Status
Informed consent was obtained from all participants in accordance with the Brigham and Women's Hospital Committee for the Protection of Human Subjects from Research Risks. Family members were screened without knowledge of genotype status by a thorough history and physical examination, ECG, and transthoracic echocardiography with color-flow Doppler. Families with Holt-Oram syndrome were evaluated as described previously.8 9 All individuals at risk for Heart-Hand syndrome Type III (family C, Fig 1
) and
selected individuals with familial ASDs and atrioventricular block
(family P, Fig 1) had radiographic studies of the upper limbs.
Heart-Hand syndrome Type III was diagnosed in family C if an individual
had gross or radiographic evidence of hand deformity with or without
associated cardiac disease. Individuals in family P were diagnosed as
affected on the basis of echocardiographic and ECG evidence of ASD and
atrioventricular block.
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Genetic Analyses
Genomic DNA was isolated from peripheral
lymphocytes as
previously described8 or from whole blood with QIAamp
columns (Qiagen). Polymorphic short tandem repeats (STRs, also termed
microsatellites) were amplified with the polymerase chain reaction
(PCR) with published nucleotide primer sequences and analyzed on
denaturing polyacrylamide-urea gels as previously
described.8
Two-point linkage analyses were performed with MLINK (V5.1), and multipoint analyses were performed with LINKMAP.10 Penetrance was set at 0.95 for all analyses. Multipoint linkage analyses were performed with polymorphic loci D12S84, DAO, and D12S79. The Holt-Oram syndrome locus is flanked by D12S84 and DAO on the centromeric side and D12S79 on the telomeric side. Loci DAO and D12S84 map 5.5 centimorgans (cM) and 6 cM, respectively, centromeric to D12S79.8 Allele frequencies were taken from published data where available and otherwise estimated from at least 30 chromosomes. The HOMOG program was used to test for heterogeneity.10
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Results |
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TopAbstractIntroductionMethods Results Discussion References |
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Clinical Evaluations
Holt-Oram Syndrome (Heart-Hand Syndrome Type I)
Evaluations of multigenerational families F, L, M, O, and Q revealed 25 individuals typically affected3 5 8 9 by the autosomal dominant Holt-Oram syndrome. All exhibited upper-arm skeletal anomalies that ranged in severity from subclinical radiographic findings of the radii or thenar bones to frank phocomelia. Cardiac manifestations, when present, included atrial (secundum type) and ventricular septal defects, an atrioventricular canal defect, and various degrees of atrioventricular block.
Heart-Hand
Syndrome Type III
Family C (Fig 1
) is a Spanish kindred
previously
described6 by one of us (F.P.) with skeletal and cardiac
disease that is inherited as an autosomal dominant trait. Three living
affected individuals had brachydactyly type C manifested as hypoplasia
of hand metacarpals and phalanges as well as an extra ossicle of the
index finger. Individuals II-1 and III-1 also exhibited hypoplasia and
aplasia of foot phalanges. Each affected individual also had cardiac
conduction system disease: individual II-1 had sick sinus syndrome;
individuals III-1 and III-4 had right bundle-branch block. None had any
evidence of cardiac septation defects.
ASD With
Atrioventricular Block
Family P (Fig 1) is a North
American kindred of Anglo-Saxon
descent previously described7 by one of us (W.E.P.). ASDs
and atrioventricular block are inherited in this family in an autosomal
dominant pattern. Eight of 14 affected individuals in this kindred were
alive and available for study. All had preoperative first-degree
atrioventricular block. Each affected individual, with the exception of
individual IV-7, had an ostium secundum ASD that required surgical
intervention. In addition, individual V-1 had a ventricular septal
defect. There were neither gross nor radiographic skeletal
abnormalities in any individuals in family P with cardiac
abnormalities.
Genetic Studies
Analyses of polymorphic STRs
("Methods") in five families
(F, L, M, O, and Q) demonstrated linkage of these Holt-Oram syndromes
to the locus previously identified on chromosome 12q2. The
HOMOG program provided further evidence of homogeneity
(>99% confidence; data not shown). Compilation of these data with
previous genetic studies8 yielded a combined multipoint
LOD (Logarithm of the Odds) score of 25 (Fig 2) and
provided odds of greater than 1025:1 that the Holt-Oram
syndrome disease gene is located on chromosome 12q2.
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Analyses of
polymorphic STRs in family C (Heart-Hand syndrome Type III)
and family P (familial ASD with atrioventricular block) excluded
linkage to the Holt-Oram syndrome locus. Multipoint LOD scores in each
family were less than -2.0 across the entire interval between D12S79
and DAO (Fig 2). Analyses with the HOMOG program
indicated
that neither Heart-Hand syndrome Type III nor familial ASD with
atrioventricular block is likely to be due to mutations in the
Holt-Oram syndrome gene on chromosome 12q2 (>99% confidence; data not
shown). Because a previous report suggested possible linkage of a gene
defect responsible for familial ASDs to the HLA locus on human
chromosome 6,11 12 additional studies were performed
in
family P. LOD scores less than -2.0 were obtained for 10 cM flanking
STR D6S105, excluding this as the genomic location of the disease gene
in family P.
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Discussion |
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TopAbstractIntroductionMethods Results Discussion References |
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We demonstrate that two disorders, Heart-Hand syndrome Type III and familial ASD accompanied by atrioventricular conduction abnormalities, are genetically distinct from the Holt-Oram syndrome. While clinically these disorders appear to be partial phenocopies of Holt-Oram syndrome, neither is genetically linked to chromosome 12q2. Combined with previous establishment of genetic loci for isolated preaxial limb deformity,13 14 these data provide clear evidence for genetic heterogeneity among syndromes that share findings of skeletal radial ray deformity, cardiac septation defects, and/or conduction system disease.
Genetic studies in family P clearly excluded the HLA locus on chromosome 611 12 as the cause of both conduction system disease and ASDs. While genetic heterogeneity of ASDs may exist, the previously proposed HLA linkage may reflect a spurious finding based on composite data derived from kindreds in which independent analyses did not provide proof of linkage.
The cardiac and limb malformations that characterize the relatively rare heart-hand syndromes frequently occur in isolation or in the setting of other multiorgan system congenital disorders that are likely to be genetically heterogeneous. For instance, patients with Fanconi's anemia may be affected by hypoplastic radii in the presence or absence of conotruncal or septal defects.15 However, since the Fanconi anemia gene defect causes increased DNA fragility, cardiac and skeletal deformity may represent direct effects of the Fanconi mutations or secondary effects on other genes such as the Holt-Oram syndrome gene. The cooccurrence of cardiac and limb deformity with genitourinary, hematological, and vascular anomalies in Kaufman-McKusick syndrome, Thrombocytopenia-Absent Radius syndrome, SC Phocomelia, or Roberts syndrome3 suggests at least some of the genes involved in these syndromes have ubiquitous actions or affect early developmental pathways that comprise a regulatory cascade in cardiac and skeletal morphogenesis.
Despite the marked genetic heterogeneity of heart-hand syndromes, genetic heterogeneity of Holt-Oram syndrome itself is at most minimal. Of 22 kindreds that we8 and others16 17 have genetically evaluated, the Holt-Oram syndrome has been shown not to be linked to the chromosome 12q2 locus in only one family. Because Holt-Oram syndrome may manifest as subtly as unilateral asymmetric radiographic carpal bone malformation,3 18 19 Terrett et al's17 diagnostic criterion of bilateral radial ray defects may account for nonlinkage in this one family. Moreover, it is possible that the unlinked disorder segregating in this family is actually a non–Holt-Oram phenocopy heart-hand syndrome. We conclude that the predominant locus for Holt-Oram syndrome is located on chromosome 12q2.
Several genes, such as homeobox genes, peptide growth factors, and retinoic acid receptors, have been proposed to contribute to cardiac and limb development. Although genomic localization excludes such known genes as the Holt-Oram syndrome gene, each remains an important candidate for the Heart-Hand syndrome Type III and the familial ASD with atrioventricular block syndrome studied here. Ongoing efforts to identify cardiac and limb morphogens will contribute to genetic analysis of all heart and hand syndromes and improve our understanding of normal development as well as congenital malformations.
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Acknowledgments |
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The authors are indebted to the members of the families, without whose generous assistance these studies would not have been possible, and to Mohammed Miri for technical assistance. This work was supported by grants from the American Heart Association (Dr Basson, Bugher Fellowship), the Wellcome Trust (Dr MacRae), the Peabody Foundation, Inc (Dr Holmes), the Howard Hughes Medical Institute (Drs J.G. and Christine Seidman), and an unrestricted grant from Bristol-Myers Squibb (Drs J.G. and Christine Seidman).
Received October 31, 1994; revision received January 3, 1995; accepted January 10, 1995.
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