Based on methylation biomarkers identified in a mouse model for ICF1 [58] and validated in a cohort of ICF1 patients [43], two ICFX patients without mutation in DNMT3B, ZBTB24, CDCA7 or HELLS were classified as ICF1-like based on typical DNAme signatures of DNMT3B LoF, which included hypomethylation of germline genes promoters and pericentromeric satellite repeats but excluded hypomethylation at alpha-satellite repeats [43]. Here, HELLS is linked to immunodeficiency-centromeric instability-facial anomalies syndrome 1.