A novel biallelic loss-of-function variant in DAND5 causes heterotaxy syndrome

Abstract

The majority of heterotaxy cases do not obtain a molecular diagnosis, although pathogenic variants in more than 50 genes are known to cause heterotaxy. A heterozygous missense variant in DAND5, a nodal inhibitor, which functions in early development for establishment of right-left patterning, has been implicated in heterotaxy. Recently, the first case was reported of a DAND5 biallelic loss-of-function (LoF) variant in an individual with heterotaxy. Here, we describe a second unrelated individual with heterotaxy syndrome and a homozygous frameshift variant in DAND5 (NM_152654.2:c.197del [p.Leu66ArgfsTer22]). Using an in vitro assay, we demonstrate that the DAND5 c.197del variant is unable to inhibit nodal signaling when compared with the wild-type expression construct. This work strengthens the genetic and functional evidence for biallelic LoF variants in DAND5 causing an autosomal recessive heterotaxy syndrome.

Keywords: abdominal situs inversus.

Figure 1.

(A) Frontal radiograph of the chest and abdomen at 8 mo of age showing heterotaxy, transverse liver, right-sided stomach with duodenal feeding tube, and cardiomegaly. (B) Pedigree showing the family of the affected individual. (C) Sanger sequencing confirmed the DAND5 homozygous variant in the proband. The genomic (hg19/GRCh37) and the cDNA coordinates are marked below the electrophoregram. (D) Localization of the two homozygous frameshift variants on the DAND5 protein; the variant seen in the current study is underlined. (E) A luciferase assay performed on HEK293T cells with a reporter gene under the control of three activin-responsive element promoters, pAR3-lux, which is transcriptionally activated strictly by Nodal together with FOXH1 and TDGF1, was used. The results showed the expression vector with the DAND5 c.197del variant does not inhibit Nodal signaling when compared with wild-type DAND5 construct. For this overexpression assay, the effect of the different genes altogether and the individual effect for each one is shown. Bars indicate standard deviation of all three experiments of four replicates. Significance: (*) P < 0.01, t-test.