In addition, Mmp21-mutant mice and mmp21-morphant zebrafish displayed heterotaxy and abnormal cardiac looping, respectively, suggesting a new role for extracellular matrix remodeling in the establishment of laterality in vertebrates.
A total of 28 candidate variants (26 rare predicted-damaging variants and 2 hemizygous deletions) were identified, including variants in genes known to cause heterotaxy and primary ciliary dyskinesia (ACVR2B, NODAL, ZIC3, DNAI1, DNAH5, HYDIN, MMP21), and genes without a human phenotype association, but with prior evidence for a role in embryonic laterality or cardiac development.
Previously we mapped a locus for situs abnormalities in humans, HTX1, to Xq26.2 by linkage analysis in a single family (LR1) and by detection of a deletion in an unrelated situs ambiguus male (Family LR2; refs 2,3).
We sought to develop a hypomorphic Zic3 mouse to model human heterotaxy and investigate developmental mechanisms underlying variability in cardiac phenotypes.
A study population of 348 patients collected over more than 10 years with a large variety of congenital heart disease including heterotaxy was screened for variants in the ZIC3 gene.
Here we summarise our current understanding of ZIC3 function and describe the potential role ZIC3 plays in important signalling pathways and their links to heterotaxy.
Patients with TGA (n = 169), double outlet right ventricle (DORV; n = 89), common atrioventricular canal (CAVC; n = 41), and heterotaxy (n = 54) underwent sequencing of ZIC3 exons.
Identified cytogenetic abnormalities ranged from large unbalanced translocations to smaller, kilobase-scale CNVs, including a rare, single exon deletion in ZIC3, a gene known to cause X-linked heterotaxy.
These results define the temporal and spatial requirements for Zic3 in node morphogenesis, left-right patterning and cardiac development and suggest the possibility that a requirement for Zic3 in node ultrastructure underlies its role in heterotaxy and laterality disorders.
Longitudinal follow-up revealed that this family has X-linked heterotaxy due to a missense mutation, c.1048A>G(R350G), in the third zinc finger domain of ZIC3.
The birth incidence of heterotaxy-spectrum malformations is significantly higher in males, but our previous work indicated that mutations within ZIC3 did not account for the male over-representation.
Here we have investigated whether variants in NODAL are present in patients with heterotaxy and/or isolated cardiovascular malformations (CVM) thought to be caused by abnormal heart tube looping.
We show that cfap53 is required for cilia rotation specifically in Kupffer's vesicle, the zebrafish laterality organ, providing a mechanism by which patients with CFAP53 mutations develop dextrocardia and heterotaxy, and confirming previous evidence that left-right asymmetry in humans is regulated through cilia-driven fluid flow in a laterality organ.
These findings show that Dnahc5 is required for the specification of left-right asymmetry and suggest that the PCD-causing Dnahc5 mutation may also be associated with heterotaxy.