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STAG1-related disorder is a cohesinopathy caused by heterozygous pathogenic variants in STAG1, which encodes the SA-1 (STAG1) subunit of the cohesin complex. The condition has been described under several names, including STAG1-related neurodevelopmental disorder and intellectual developmental disorder, autosomal dominant 47 (MRD47).

Affected individuals typically present with global developmental delay, intellectual disability, and marked speech delay, often accompanied by hypotonia and delayed motor milestones in infancy. Behavioural features are common and may include autism spectrum disorder. Epilepsy occurs in a subset of patients, with variable seizure types. Facial dysmorphism is generally mild and non-specific, with features such as a broad forehead, deep-set eyes, and a wide mouth observed. Additional findings described in smaller numbers of individuals include vision or hearing impairment, congenital heart defects, and musculoskeletal anomalies such as scoliosis, joint laxity, or limb differences.

To date, only a few dozen affected individuals have been reported worldwide, so the true prevalence is unknown but is considered to be very rare. Inheritance is autosomal dominant, with most reported variants occurring de novo. Familial cases with vertical transmission and intrafamilial variable expressivity have been described, including monozygotic twins with different severity, indicating incomplete penetrance and significant phenotypic variability. There is currently no estimate of life expectancy, but available reports suggest that many individuals survive into childhood and adulthood with persistent neurodevelopmental disability.