These findings suggest that DNVs may also contribute to mutational load in multiplex BD families, as previously observed for multiplex autism families.6 Although this study is limited by the small sample size, the overall de novo mutation rate was comparable in cases and unaffected offspring, whereas deleterious DNVs were observed more frequently in participants with BD, which is consistent with previous reports in autism and schizophrenia.2 This study highlighted HP, PC, MAP4, and WDHD1 as potential susceptibility genes for BD. Here, PC is linked to autism.