Background: Schaaf-Yang syndrome is an ultra-rare neurodevelopmental disorder caused by pathogenic variants in the MAGEL2 gene, also implicated in Prader-Willi syndrome. With less than 1 case per 50 000 people, Schaaf-Yang syndrome remains underreported globally, and no previous cases have been documented in Brazil. Case description: This study presents a 4-year-old Brazilian girl clinically diagnosed with Prader-Willi syndrome, characterized by hypotonia, delayed neuropsychomotor development, and craniofacial dysmorphism. Initial assessments identified growth hormone deficiency and developmental delays, followed by genetic sequencing at 2 years of age, confirming a pathogenic MAGEL2 variant [NM_019066.5:c2821dup: p (Arg941Profs*10)]. The child was also diagnosed with autism spectrum disorder. Multidisciplinary interventions, including medical care, speech therapy, and psychological support, led to remarkable improvements in motor function, language, memory, and learning. Conclusions: This is the first documented Brazilian case of Schaaf-Yang syndrome, emphasizing the critical role of early diagnosis and personalized interventions in reducing the impact of the syndrome.
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