Phenotypic expansion in <i> <scp>DDX</scp> 3X </i> – a common cause of intellectual disability in females

De <i>novo</i> variants in <i>DDX3X</i> account for 1-3% of unexplained intellectual disability (ID) cases and are amongst the most common causes of ID especially in females. Forty-seven patients (44 females, 3 males) have been described. We identified 31 additional individuals carrying 29 unique <i>DDX3X</i> variants, including 30 postnatal individuals with complex clinical presentations of developmental delay or ID, and one fetus with abnormal ultrasound findings. Rare or novel phenotypes observed include respiratory problems, congenital heart disease, skeletal muscle mitochondrial DNA depletion, and late-onset neurologic decline. Our findings expand the spectrum of DNA variants and phenotypes associated with <i>DDX3X</i> disorders.