Congenital disorder of glycosylation (CDG) Ia is an autosomal recessive disorder caused by a deficiency of phosphomannomutase. This enzyme normally catalyzes the conversion of mannose-6-phosphate to mannose-1-phosphate. This step is required for the addition of N-linked sugars to proteins. Patients will present with hypotonia and developmental delay along with other symptoms including failure to thrive, abnormal fat distribution, seizures, stroke-like episodes and/or esotropia. Clinical presentation ranges from significantly affected infants to adolescents and adults with more minor involvement.