Glycosylphosphatidylinositol Biosynthesis Defect 15, also known as developmental delay, epilepsy, cerebellar atrophy, and osteopenia, is related to epilepsy and hypotonia. An important gene associated with Glycosylphosphatidylinositol Biosynthesis Defect 15 is GPAA1 (Glycosylphosphatidylinositol Anchor Attachment 1). Related phenotypes are seizure and eeg abnormality