ZNF423patient variants, truncations, and in-frame deletions in mice define an allele-dependent range of midline brain abnormalities

Abstract

Interpreting rare variants remains a challenge in personal genomics, especially for disorders with several causal genes and for genes that cause multiple disorders.ZNF423 encodes a transcriptional regulatory protein that intersects several developmental pathways. ZNF423 has been implicated in rare neurodevelopmental disorders, consistent with midline brain defects in Zfp423-mutant mice, but pathogenic potential of most patient variants remains uncertain. We engineered ~50 patient-derived and small deletion variants into the highly-conserved mouse ortholog and examined neuroanatomical measures for 791 littermate pairs. Three substitutions previously asserted pathogenic appeared benign, while a fourth was effectively null. Heterozygous premature termination codon (PTC) variants showed mild haploabnormality, consistent with loss-of-function intolerance inferred from human population data. In-frame deletions of select zinc fingers showed mild to moderate abnormalities, as did low-expression variants. These results affirm the need for functional validation of rare variants in biological context and demonstrate cost-effective modeling of neuroanatomical abnormalities in mice.(149 words)

Strain-dependent modifier genes determine survival inZfp423mice

“…Both survival and behavioral ataxia were substantially more penetrant on B6 than BALB, although statistical support for anatomical differences were sub-threshold and likely underpowered relative to the observed variance. This strain difference in sensitivity contrasts with recent work in our lab comparing different alleles on a single inbred background, where anatomical differences were more sensitive than behavior in a more extensive series of animals [17]. Surviving Zfp423 nur12 mutants from intercross and backcross designs reported here showed that no single locus is either necessary or sufficient for mutant survival, but taken together, our results supported the existence of a modifier locus on chromosome 5, with suggestive or significant support for linkage at other loci being cross-dependent.…”

“…This suggests that searches for survival loci might be more powerful in strains with low survival frequency and close relation to B6, as these should limit the number of contributing loci and therefore the statistical power per surviving mutant. These results also informed our choice of strains for modeling patient variants of uncertain significance [17], where FVB provided a high-survival, yet fullypenetrant background compatible with recovery of severe alleles and B6 provided a sensitized background to increase confidence in negative findings [17].…”

“…Mutations in the human homolog ZNF423 have been reported in patients with ciliopathy diagnoses and anatomical findings reminiscent of Zfp423 mutant mice [7] and a subset of patient mutations has been validated in mouse models [17].…”