Genetic basis of inosine triphosphate pyrophosphohydrolase deficiency.
Inosine triphosphate pyrophosphohydrolase (ITPase) deficiency is a common inherited condition characterized by the abnormal accumulation of inosine triphosphate (ITP) in erythrocytes. The genetic basis and pathological consequences of ITPase deficiency are unknown. We have characterized the genomic structure of the ITPA gene, showing that it has eight exons. Five single nucleotide polymorphisms were identified, three silent (138G-->A, 561G-->A, 708G-->A) and two associated with ITPase deficiency (94C-->A, IVS2+21A-->C). Homozygotes for the 94C-->A missense mutation (Pro32 to Thr) had zero erythrocyte ITPase activity, whereas 94C-->A heterozygotes averaged 22.5% of the control mean, a level of activity consistent with impaired subunit association of a dimeric enzyme. ITPase activity of IVS2+21A-->C homozygotes averaged 60% of the control mean. In order to explore further the relationship between mutations and enzyme activity, we examined the association between genotype and ITPase activity in 100 healthy controls. Ten subjects were heterozygous for 94C-->A (allele frequency: 0.06), 24 were heterozygotes for IVS2+21A-->C (allele frequency: 0.13) and two were compound heterozygous for these mutations. The activities of IVS2+21A-->C heterozygotes and 94C-->A/IVS2+21A-->C compound heterozygotes were 60% and 10%, respectively, of the normal control mean, suggesting that the intron mutation affects enzyme activity. In all cases when ITPase activity was below the normal range, one or both mutations were found. The ITPA genotype did not correspond to any identifiable red cell phenotype. A possible relationship between ITPase deficiency and increased drug toxicity of purine analogue drugs is proposed.
Sumi
Satoshi
S
Purine Research Unit, Department of Chemical Pathology, 5th Floor Thomas Guy House, Guy's and St. Thomas' Hospitals, London, SE1 9RT, UK.
Marinaki
Anthony M
AM
Arenas
Monica
M
Fairbanks
Lynette
L
Shobowale-Bakre
Monsor
M
Rees
David C
DC
Thein
Swee Lay
SL
Ansari
Azhar
A
Sanderson
Jeremy
J
De Abreu
Ronney A
RA
Simmonds
H Anne
HA
Duley
John A
JA
D000328:Adult; D001483:Base Sequence; D002648:Child; D018076:DNA, Complementary; D005260:Female; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011755:Pyrophosphatases / Q000737:chemistry / Q000172:deficiency / Q000235:genetics*; D000097630:Inosine Triphosphatase
D018076:DNA, Complementary; D011755:Pyrophosphatases; D000097630:Inosine Triphosphatase