HELLS and ICF syndrome: Mutations in four genes are known to cause ICF syndrome: the de novo DNA methyltransferase DNMT3B, the SNF2-family adenosine triphosphatase (ATPase) HELLS (also known as LSH, SMARCA6, or PASG), the HELLS activator CDCA7, and the transcription factor ZBTB24, which is critical for the expression of CDCA7 (6–8).