ATP7B and Wilson disease: It is also possible that homozygotes require additional risk factors (genetic or not) to develop Wilson disease, such as common hypofunctional variants impacting ATP7B. The only reported homozygous case belonged to a pediatric group with median age at diagnosis of 7.4 years and maximum age at diagnosis of 21 years, but an additional pathogenic variant may have been missed because not all exons were sequenced10.