Onset of symptoms is normally within the first year of life with truncal ataxia and seizures.

Common facial abnormalities include: [citation needed] Other common features include:[citation needed] The associated intellectual disability is usually in the profound range.

Those affected often have a happy demeanor with frequent smiling and spontaneous laughter.

Mutations in this gene cause a decrease in the pH (overacidification) of the endosomes.

[citation needed] The prevalence is not known but this is considered to be a rare disease.