Main clinical characteristics include seizures, microcephaly (small head size), cataracts (cloudiness of the lens which makes vision blurry), feeding difficulties, failure to thrive, repetitive hand movements, and delayed brain myelination. Almost all families report cyclical bouts of extreme irritability and inconsolability. Most have significant delays with development, and many are unable to walk or speak. Hypotonia (low muscle tone), sleep disorders, breath-holding spells, and repetitive movements such as hand flapping or hand wringing are common. Individuals tend to have a broad tip of the nose but otherwise have typical facial characteristics.
Individuals with a genetic change in the NACC1 gene other than the one that has been studied (c.892C>T/p.Arg298Trp variant) may have less specific symptoms including developmental delay, intellectual disability, and/or autism, but more studies are needed in order to better understand these differences.