Finnish type of sialic acid storage disease with sialuria (Salla disease): the occurrence and diagnostic significance of cytoplasmic vacuoles in blood lymphocytes

In this study peripheral blood smears from 29 patients (17 males and 12 females; mean age 28 years, range 3-65 years) with a confirmed diagnosis of the Finnish type of sialic acid storage disease (FSASD) and 200 controls with mental retardation without any evidence of metabolic disease were examined for the presence of vacuolated lymphocytes. Urine samples were analysed by thin-layer chromatography for free sialic acid. Only 62% of the patients with FSASD had a clearly increased percentage of vacuolated lymphocytes (greater than normal mean + 2 s.d.). In thin-layer chromatography all the FSASD patients gave a positive test result. No false positive or negative results were obtained. Electronmicroscopical examination of peripheral blood lymphocytes demonstrated only non-specific changes in a few cells. Examination of peripheral lymphocytes for vacuoles is not a reliable screening test for FSASD. The screening method of choice is the analysis of free sialic acid by thin-layer chromatography.