ZNF445: a homozygous truncating variant in a patient with Temple syndrome and multilocus imprinting disturbance.

BACKGROUND

ZNF445, as well as ZFP57, is involved in the postfertilization methylation maintenance of multiple imprinting-associated differentially methylated regions (iDMRs). Thus, ZNF445 pathogenic variants are predicted to cause multilocus imprinting disturbances (MLIDs), as do ZFP57 pathogenic variants. In particular, the MEG3/DLK1:IG-DMR would be affected, because the postzygotic methylation imprint of the MEG3/DLK1:IG-DMR is maintained primarily by ZNF445, whereas that of most iDMRs is preserved by both ZFP57 and ZNF445 or primarily by ZFP57.

RESULTS

We searched for a ZNF445 variant(s) in six patients with various imprinting disorders (IDs) caused by epimutations and MLIDs revealed by pyrosequencing for nine iDMRs, without a selection for the original IDs. Re-analysis of the previously obtained whole exome sequencing data identified a homozygous ZNF445 variant (NM_181489.6:c.2803C>T:p.(Gln935*)) producing a truncated protein missing two of 14 zinc finger domains in a patient with Temple syndrome and MLID. In this patient, array-based genomewide methylation analysis revealed severe hypomethylation of most CpGs at the MEG3:TSS-DMR, moderate hypomethylation of roughly two-thirds of CpGs at the H19/IGF2:IG-DMR, and mild-to-moderate hypomethylation of a few CpGs at the DIRAS3:TSS-DMR, MEST:alt-TSS-DMR, IGF2:Ex9-DMR, IGF2:alt-TSS, and GNAS-AS1:TSS-DMR. Furthermore, bisulfite sequencing analysis for the MEG3/DLK1:IG-DMR delineated a markedly hypomethylated segment (CG-A). The heterozygous parents were clinically normal and had virtually no aberrant methylation pattern.

CONCLUSIONS

We identified a ZNF445 pathogenic variant for the first time. Since ZNF445 binds to the MEG3/DLK1:IG-DMR and other iDMRs affected in this patient, the development of Temple syndrome and MLID would primarily be explained by the ZNF445 variant. Furthermore, CG-A may be the target site for ZNF445 within the MEG3/DLK1:IG-DMR.