Individuals with type I are asymptomatic.
Seizures (grand mal, petit mal) and mental retardation have been associated
with type II. Elevated cerebrospinal fluid (CSF) concentrations for
gamma-aminobutyric acid (GABA), glutamate, and proline
have been described in some patients, but their association with neurologic
manifestations remains undetermined. Intestinal absorption of proline may be
impaired. Heterozygotes have glycinuria only (plasma levels of amino acids
are normal). Other features include dry skin, chronic inflammatory lung
disease, sensorineural deafness, and ichthyosis.