Identification and Functional Analysis of ZIC3 Mutations in Heterotaxy and Related Congenital Heart Defects

Abstract

Mutations in the zinc finger transcription factor ZIC3 cause X-linked heterotaxy and have also been identified in patients with isolated congenital heart disease (CHD). To determine the relative contribution of ZIC3 mutations to both heterotaxy and isolated CHD, we screened the coding region of ZIC3 in 194 unrelated patients, including 61 patients with classic heterotaxy, 93 patients with heart defects characteristic of heterotaxy, and 11 patients with situs inversus totalis. Five novel ZIC3 mutations in three classic heterotaxy kindreds and two sporadic CHD cases were identified. None of these alleles was found in 97 ethnically matched control samples. On the basis of these analyses, we conclude that the phenotypic spectrum of ZIC3 mutations should be expanded to include affected females and CHD not typical for heterotaxy. This screening of a cohort of patients with sporadic heterotaxy indicates that ZIC3 mutations account for approximately 1% of affected individuals. Missense and nonsense mutations were found in the highly conserved zinc finger-binding domain and in the N-terminal protein domain. Functional analysis of all currently known ZIC3 point mutations indicates that mutations in the putative zinc finger DNA binding domain and in the N-terminal domain result in loss of reporter gene transactivation. It is surprising that transfection studies demonstrate aberrant cytoplasmic localization resulting from mutations between amino acids 253-323 of the ZIC3 protein, indicating that the pathogenesis of a subset of ZIC3 mutations results at least in part from failure of appropriate nuclear localization. These results further expand the phenotypic and genotypic spectrum of ZIC3 mutations and provide initial mechanistic insight into their functional consequences.

Rare novel variants in the ZIC3 gene cause X-linked heterotaxy

“…31,33,34 Additionally we did not identify any suspicious variants in patients with isolated TGA (30 patients with TGA, included in the subgroup cyanotic heart disease) comparable to earlier reports. 24,31,34 The final classification of variants in this study was based on a combination of in silico analysis as described in the Materials and Methods, together with functional data generated in this study as well as data from earlier publications.…”

Situs ambiguus in a female fetus with balanced (X;21) translocation – evidence for functional nullisomy of the ZIC3 gene?

“…Heterozygous females had milder malformations including situs ambiguus and anal anomalies. 3,21 Recently, ZIC3 mutations have also been identified in patients with isolated congenital heart disease. 21 The cardiac malformations comprised a combination of anomalies of the venous inflow and arterial outflow tract, such as single atrium, single ventricle, persistent atrioventricular canal (AVC), VSD or ASD (corrected), transposition of the great arteries (TGA) or right descending aorta, pulmonic stenosis or atresia (PS) and often dextroposition of the heart and right descending aorta.…”

“…3,21 Recently, ZIC3 mutations have also been identified in patients with isolated congenital heart disease. 21 The cardiac malformations comprised a combination of anomalies of the venous inflow and arterial outflow tract, such as single atrium, single ventricle, persistent atrioventricular canal (AVC), VSD or ASD (corrected), transposition of the great arteries (TGA) or right descending aorta, pulmonic stenosis or atresia (PS) and often dextroposition of the heart and right descending aorta. Our case displaying right-sided situs ambiguus with asplenia, bilaterally four-lobed lungs, malrotation of the intestine and a characteristic heart defect (AVC þ TGA þ PS) and also anal ectopia and sacral hypoplasia fits well into the malformation spectrum of the above male cases, with the exception that it lacked a mutation in ZIC3 and that it concerned a female with a balanced 46,X,t(X;21)(q26;p13) chromosome translocation.…”

Heterotaxy and cardiac defect in a girl with chromosome translocation t(X;1)(q26;p13.1) and involvement of ZIC3

“…2 -6 ZIC3-associated heterotaxy is an X-linked recessive disorder of variable clinical expression that predominantly affects males, but one heterozygous female with isolated congenital heart defect has also been reported. 4 In females, constitutional X-autosome translocations with one breakpoint in the ZIC3 region can lead to functional nullisomy of ZIC3 by suppressed expression of the gene on the translocation chromosome (caused by disruption of the gene, or position effects) and preferential inactivation of the normal X-chromosome. This situation has recently been reported in a female foetus with a balanced translocation t(X;21)(q26;p13) and the clinical features of ZIC3 mutations (situs ambiguus and cardiac malformations).…”