Sort of a mild version of sleep apnea, UARS is both much more more common, and much harder to detect.

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The Smith-Magenis Syndrome Foundation UK said major features of the condition include mild to moderate intellectual disability, delayed speech and language skills, distinctive facial features, sleep disturbances, and behavioural problems.

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"If you have very severe sleep apnea, it's unlikely to miss it, but if you have mild apnea, it might, " says Douglas Kirsch, an instructor at Harvard Medical School.

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