Clinical, biochemical and genetic findings in two siblings with a dihydropyrimidinase deficiency.
Dihydropyrimidinase (DHP) is the second enzyme of the pyrimidine degradation pathway and it catalyses the ring opening of 5,6-dihydrouracil and 5,6-dihydrothymine to N-carbamyl-beta-alanine and N-carbamyl-beta-aminoisobutyric acid, respectively. To date, only nine individuals have been reported suffering from a complete DHP deficiency. We report two siblings presenting with strongly elevated levels of 5,6-dihydrouracil and 5,6-dihydrothymine in plasma, cerebrospinal fluid and urine. One of the siblings had a severe delay in speech development and white matter abnormalities, whereas the other one was free of symptoms. Analysis of the DHP gene (DPYS) showed that both patients were compound heterozygous for the missense mutation 1078T>C (W360R) in exon 6 and a novel missense mutation 1235G>T (R412M) in exon 7. Heterologous expression of the mutant enzymes in Escherichia coli showed that both missense mutations resulted in a mutant DHP enzyme without residual activity. Analysis of the crystal structure of eukaryotic DHP from the yeast Saccharomyces kluyveri and the slime mold Dictyostelium discoideum suggests that the W360R and R412M mutations lead to structural instability of the enzyme which could potentially impair the assembly of the tetramer.
van Kuilenburg
André B P
AB
Academic Medical Center, University of Amsterdam, Emma Children's Hospital, P.O. Box 22700, 1100 DE Amsterdam, The Netherlands. a.b.vankuilenburg@amc.uva.nl
Meijer
Judith
J
Dobritzsch
Doreen
D
Meinsma
Rutger
R
Duran
Marinus
M
Lohkamp
Bernhard
B
Zoetekouw
Lida
L
Abeling
Nico G G M
NG
van Tinteren
Herman L G
HL
Bosch
Annet M
AM
D000581:Amidohydrolases / Q000096:biosynthesis / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000002:abnormalities; D002675:Child, Preschool; D018360:Crystallography, X-Ray; D004023:Dictyostelium / Q000201:enzymology; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology; D006801:Humans; D007805:Language Development Disorders / Q000503:physiopathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D011487:Protein Conformation; D012440:Saccharomyces / Q000201:enzymology; D035781:Siblings; D013941:Thymine / Q000031:analogs & derivatives / Q000097:blood / Q000134:cerebrospinal fluid / Q000652:urine; D014498:Uracil / Q000031:analogs & derivatives / Q000097:blood / Q000134:cerebrospinal fluid / Q000652:urine
C007419:dihydrouracil; D014498:Uracil; C042836:5,6-dihydrothymine; D000581:Amidohydrolases; C020047:dihydropyrimidinase; D013941:Thymine