To the Editor:
Recently, an interesting observation has been reported by Gebbia et al1 in this journal regarding connexin43 gene mutations in patients with heterotaxy. Previously, another paper was published by Britz-Cunningham et al2 reporting human connexin43 gene mutations in patients with visceroatrial heterotaxy syndrome. Their article was referred to in the McKusick catalogue in the description of Ivemark syndrome (MIM 208530),3 and connexin43 mutations were thought to be the cause of asplenia and polysplenia syndromes with cardiovascular anomalies. Only some hundred such cases have been reported so far in the literature, and most of them were sporadic, although familiar occurrences have also been described, suggesting autosomal recessive inheritance.3 The first evidence for the autosomal recessive inheritance was the identification of connexin43 gene mutations in these patients by Britz-Cunningham et al.2 Two other groups examined connexin43 mutations in patients with heterotaxy syndromes, but neither of them could detect any mutation in the cytoplasmic carboxy terminal region of the gene.4 5 Gebbia and colleagues1 continued the search for mutation in additional patients with sporadic and familial heterotaxy, but they could not detect any connexin43 mutation in any patients with heterotaxy. Because only three groups have reported the investigation of connexin43 mutations so far in heterotaxy syndromes, and because there was a striking difference in their results, we sequenced that critical region of the connexin43 gene in our Hungarian patients with heterotaxy. DNA from 11 individuals was amplified by polymerase chain reaction and sequenced6 similarly to the reported method.2 One case was familial and has been reported elsewhere7 ; the other cases were sporadic. Most of them were diagnosed prenatally by echocardiography. In all cases, the embryopathological examination of the fetus after induced abortion or autopsy proved heterotaxy with asplenia or polysplenia and cardiovascular anomalies. In 2 cases, there were no available tissues for the examination, and only the parents’ DNA was sequenced. None of the examined DNA contained a mutation in the carboxy terminal region of the connexin43 gene. We agree with Gebbia et al that mutations in the terminal 400 bp of the connexin43 coding region probably do not account for heterotaxy cases. So far, 48 patients’ DNA has been sequenced in connection with connexin43 mutations. Six patients were reported by Britz-Cunningham,2 12 by Penman Splitt et al,5 19 by Gebbia et al,1 and 11 by us. It is strange that only patients reported by Britz-Cunningham et al carried a mutation in this gene and even stranger that all of them carried one or two connexin43 mutations whereas the other 42 patients did not carry any mutation in that region of the connexin43 gene. On the basis of the results of Gebbia et al and our observations, we believe that it is more and more likely that the results reported by Britz-Cunningham et al were a laboratory artifact. We should consider changing the description of Ivemark syndrome in the McKusick catalogue regarding connexin43 mutations.
- Copyright © 1998 by American Heart Association
Gebbia M, Towbin JA, Casey B. Failure to detect connexin43 mutations in 38 cases of sporadic and familial heterotaxy. Circulation. 1996;94:1909–1912.
McKusick VA. Mendelian Inheritance in Man. CD-ROM; Johns Hopkins University, September 29, 1995.
Penman Splitt M, Burn J, Goodship J. Connexin43 mutations in sporadic and familial defects of laterality. N Engl J Med. 1995;333:941–942.
We have read with interest the letter to the Editor of Toth et al describing their inability to detect connexin43 (cx43) mutations in 11 cases of heterotaxy. The negative results of Toth et al now brings to 78 the number of reported heterotaxy cases in which no cx43 mutations could be found in the 200 base pairs containing all of the nucleotide changes reported by Britz-Cunningham et al.R1 R2 R3 Mice either lacking or overexpressing cx43 develop right-heart outflow obstruction, but the complex cardiac and extracardiac malformations typical of heterotaxy have not been observed.R4 R5 The absence of animal-model data to support a role of cx43 in mammalian left-right axis development as well as the inability of three independent groups to detect cx43 mutations in a large number of heterotaxy cases suggests the possibility of laboratory artifact underlying the original detection of “mutations” reported by Britz-Cunningham et al.
Family studies indicate that heterotaxy is likely to be quite heterogeneous genetically.R6 For example, we have identified recently a gene for X-linked heterotaxy,R7 mutations in which appear to account for only a minority of cases in males (K. Kosaki et al, unpublished observations). Given this genetic heterogeneity, it was surprising that Britz-Cunningham et al detected cx43 mutations in all of the heterotaxy cases that they studied.
We agree that the accumulating negative data counsel caution in drawing connections between cx43 and heterotaxy, particularly in such frequently consulted reference works as On-line Mendelian Inheritance in Man (Internet address: http://www.ncbi.nlm.nih.gov/Omim/). Reproduction of the original results by an independent laboratory may be the most efficient approach to resolving this issue.
Gebbia M, Towbin J, Casey B. Failure to detect connexin43 mutations in 38 cases of sporadic and familial heterotaxy. Circulation. 1996;94:1909–1912.
Penman-Splitt M, Tsai M, Burn J, Goodship J. Absence of mutations in the regulatory domain of the gap junction protein connexin 43 in patients with visceroatrial heterotaxy. Heart. 1997;77:369–370.
Britz-Cunningham S, Shah M, Zuppan C, Fletcher W. Mutations of the connexin43 gap-junction gene in patients with heart malformations and defects of laterality. N Engl J Med. 1995;332:1323–1329.
Reaume A, de Sousa P, Kulkarni S, Langille B, Zhu D, Davies T, Juneja S, Kidder G, Rossant J. Cardiac malformation in neonatal mice lacking Connexin43. Science. 1995;267:1831–1834.
Ewart JL, Cohen MF, Meyer RA, Huang GY, Wessels A, Gourdie RG, Chin AJ, Park SM, Lazatin BO, Villabon S, et al. Heart and neural tube defects in transgenic mice overexpressing the Cx43 gap junction gene. Development. 1997;124:1281–1292.
Kosaki K, Casey B. Genetic aspects of human left-right axis malformations. Semin Cell Dev Biol. In press.
Gebbia M, Ferrero GB, Pilia G, Aylsworth AS, Penman-Splitt M, Bird LM, Bamforth JS, Burn J, Schlesinger D, Nelson DL, Casey B. X-linked situs inversus and situs ambiguus result from mutations in the zinc-finger transcription factor ZIC3. Nat Genet. In press.