The detailed assay of [alpha]-L-iduronidase in DBFP samples has been published elsewhere (2).
The residual enzyme activities found in DBFP samples from homozygotes are shown in Table 3, expressed as a percentage of the mean of adult controls.
The interassay CVs for DBFP samples studied on five different occasions within 1 month were [less than or equal to] 9% for the fluorescent methods and [less than or equal to] 14% for the iduronate sulfatase assay.
A positive correlation was found between the leukocyte count in blood and the degree of enzyme activity measured in DBFP samples.
The different enzyme activities present in plasma and blood cells explain the nonlinear correlation between the enzyme activities from DBFP and leukocyte samples (data not shown).
There were no significant changes in enzyme activity of DBFP samples after storage for 21 days at -20[degrees]C, 4[degrees]C, or 25[degrees]C.
Assay imprecision was calculated by replicate analysis of the DBFP from a health control ([alpha]-iduronidase activity, 61.
DBFP samples from MPS I patients showed iduronidase activities [less than or equal to] 8% and 6% of the mean values of adult and newborn controls, respectively.
This fact does not modify the recognition of MPS I patients and controls, and it usually is enough time to mail the DBFP sample to a specialized laboratory for analysis.
The iduronidase activity test in DBFP samples appears to be a reasonable approach for the initial diagnosis of MPS I.
Van Hove (Department of Pediatrics, University Hospital Gasthuisberg, Leuven, Belgium) for providing DBFP samples from affected patients.