The full clinical picture is usually evident by the first year of life. Growth failure and failure to thrive are rapidly progressive. Birthweight and length may be decreased at birth. Linear growth decelerates during the first year and ceases by age 2 years. Head circumference usually is preserved.
Developmental delay is severe and often the presenting symptom.
Infants smile and follow and grasp objects, but they are unable to roll over or support weight on their legs. Generalized hypotonia and poor head control are present. Motor delay is usually more severe than cognitive delay. A wide degree of variability among patients with I-cell disease may exist. The characteristic facies is similar to that of Hurler syndrome.