👤 Ulrich Finckh

Carbamoyl-phosphate synthetase I (CPS1) deficiency (CPS1D), a recessively inherited urea cycle error due to CPS1 gene mutations, causes life-threatening hyperammonemia. The disease-causing potential of missense mutations in CPS1 deficiency can be ascertained with the recombinant CPS1 expression and purification system reported here, which uses baculovirus and insect cells. We study with this system the effects of nine clinical mutations and one polymorphism on CPS1 solubility, stability, activity, and kinetic parameters for NAG. Five of the mutations (p.T471N, p.Q678P, p.P774L, p.R1453Q, and p.R1453W) are first reported here, in three severe CPS1D patients. p.P774L, p.R1453Q, and p.R1453W inactivate CPS1, p.T471N and p.Y1491H greatly decrease the apparent affinity for NAG, p.Q678P hampers correct enzyme folding, and p.S123F, p.H337R, and p.P1411L modestly decrease activity. p.G1376S is confirmed a trivial polymorphism. The effects of the C-terminal domain mutations are rationalized in the light of this domain crystal structure, including the NAG site structure [Pekkala et al. Biochem J 424:211-220]. The agreement of clinical observations and in vitro findings, and the possibility to identify CPS1D patients who might benefit from specific treatment with NAG analogues because they exhibit reduced affinity for NAG highlight the value of this novel CPS1 expression/purification system. Show less

Carbamoyl phosphate synthetase I (CPS1) deficiency is an autosomal recessive metabolic disorder affecting the first enzymatic step of urea cycle. We report a consanguineous family in which the index patient died at 11 days of age from a severe form of CPS1 deficiency. Initial diagnosis was based on clinical histopathological, and enzymatic investigations. Direct sequencing of the complete CPS1 coding region revealed a disease-associated homozygous Thr544Met mutation in CPS1. On the basis of the molecular data, prenatal diagnosis was established for genomic DNA and performed at gestational week 12, after chorionic villus sampling. The fetus was homozygous for the Thr544Met mutation, and termination of pregnancy was elected. Histopathological signs of the hepatocellular metabolic disorder similar to that of the index patient were found in fetal liver thus giving morphological evidence for this hereditary error of urea cycle function as early as gestational week 12. Show less