ZC4H2-associated rare disorder (ZARD) is caused by pathogenic variations in the ZC4H2 gene on the X chromosome. This gene codes for a zinc finger protein involved in neural development. ZARD is characterized by highly variable symptoms, potentially influenced by the sex of the individual.

The ZC4H2-Associated Rare Disorder Natural History Study is a prospective natural history study conducted among individuals with ZARD that consists of standardized interviews, developmental assessments, and neurological examinations conducted every six months for two years. In this article, we present data from baseline visits with 40 participants, the largest ZARD cohort studied thus far, focusing on genotype-phenotype correlations and sex differences. Fisher exact, maximum likelihood χ², and Mann-Whitney tests were utilized.

Males tended to have maternally inherited ZC4H2 pathogenic variations, whereas females tended to have de novo variations (P < 0.001). Female participants were more likely to have contractures at birth (P < 0.01), arthrogryposis multiplex congenita (P < 0.001), spasticity on examination (P < 0.1), and lower limb muscle atrophy (P < 0.05). Male participants were more likely to have seizures (P < 0.1), intermittent pain (P < 0.01), severe vision impairment (P < 0.05), dysphagia for solids (P < 0.01), and generalized muscle atrophy (P < 0.05).

Our study suggests there is significant overlap in severity and range of symptoms between males and females, although several symptoms are more common in one sex than the other. Further analysis is needed to better understand how pathogenic variation type affects phenotype.