Urinary sialic acid screening in neurologic disorders

Urine sialic acid was measured in 246 patients evaluated for possible neurodegenerative disorders. Total, free, and bound sialic acid excretion declined significantly with patients' ages. Among 11 patients (4.5%) with age-related excretion rates greater than 2 standard deviations above the mean, 5 had the following disorders: free sialic acid storage disease, mucolipidosis type II, pseudohypoparathyroidism, sinus histiocytosis, and probable Sanfilippo syndrome. Although the remaining 6 were undiagnosed, 2 exhibited deteriorating courses and the other 4 presented variable combinations of organomegaly, developmental delay or mental retardation, seizures, facial dysmorphism, or bony abnormalities. Thus, these individuals also may have metabolic disorders with abnormal excretions of sialic acid-containing compounds. With awareness of age-related excretion rates, sialic acid screening is most useful for the sialidoses, mucolipidoses, and disorders of free sialic acid metabolism.