It is due to the heterozygous missense mutation p.(Pro602Leu) in the ATPase sarcoplasmic/endoplasmic reticulum Ca<sup>2+</sup> transporting 2 (<i>ATP2A2</i>) gene, which is also involved in Darier disease (DD), and is therefore considered an allelic form of DD. The gene discussed is ATP2A2; the disease is Darier disease.