Multi-locus imprinting disturbances in a family harboring a ZFP57 truncation

We previously reported a child with transient neonatal diabetes mellitus (TNDM), who upon molecular diagnosis was homozygous for a one base-pair deletion in ZFP57, inheriting the mutations from both heterozygous parents. Methylation profiling at diagnosis revealed severe hypomethylation at PLAGL1 and mosaic loss-of-methylation (LOM) at GRB10, NAP1L5 and GNAS-XL DMRs. Some years after the first child, a second sibling was born with a comparable clinical presentation. Upon molecular investigation this child was shown to have the same homozygous deletion. Using Illumina Infinium BeadChip arrays, we confirmed similar hypomethylated signatures at ubiquitous imprinted DMRs. To further characterize the stability of the imprinting defects and understand the role of this mutation in tissue-specific mosaicism, we hybridised buccal-derived DNA and a second leukocyte sample from first child to the HumanMethylationEPIC arrays. When comparing the two blood-derived samples, we observed that the hypomethylation signature is stable over time with the PLAGL1 DMR being the most severely affected, consistent with this being the disease-causing locus. Furthermore, when comparing the leukocyte and buccal samples, the same imprinted DMRs were affected to a similar extent. Bisulphite converted DNA from blood (two samples at different times), saliva (one sample) and lymphoblasts (one sample) of an individual carrying a homozygotic ZFP57 mutation, a blood sample from his brother (carrying also the same homozygotic mutation) and another blood sample from their mother (heterozygotic carrier of the mutation) were hybridized to the Illumina Infinium HumanMethylationEPIC and HumanMethylation450 BeadChips.