MECP2 and Global developmental delay: • After obtaining a detailed medical, developmental, and family history for patients with ID/GDD, if a specific etiology is considered, perform appropriate testing such as single gene testing, metabolic testing, or XLID panel. • If a specific etiology is not suspected, perform CMA (or, if not possible, karyotype and subtelomeric FISH) for all individuals with ID/GDD, MECP2 testing for females with moderate to severe ID/GDD, and FMR1 repeat analysis in all individuals with mild ID/GDD. • If these and other etiologic work-ups are negative, consider a referral to genetics.