Arginine esterase in amniotic fluid: possible marker for cystic fibrosis [letter].

Following Rao and Nadlers' report of decrease arginine activity in the blood 
of patients with cystic fibrosis we have been trying to apply 
their findings to the prenatal diagnosis of cystic fibrosis. We were 
therefore most interested in the reports on the use of 4-methylumbelliferyl-rho-guanidinobenzoate 
(MUGB) for assaying arginine esterase activity in amniotic fluid. Our results 
with MUGB are similar to those of Brock and Haywood but 
are substantially higher than those of Walsh and Nedler. A sample 
of amniotic fluid that had been incubated with MUGB and then 
assayed with pro-phe-arg-4-methylcoumarinyl-7-amide (PPA-MCA) showed less than 20% of the activity 
of a similarly treated control sample that had not been incubated 
with MUGB. The activity of arginine esterase towards PPA-MCA both in 
amniotic fluid and in cultures amniotic fluid cells is much greater 
than towards CBZ-Arg-AMC. These levels of activity are high enough to 
warrant further investigation for use in an antenatal diagnosis. 