Deficiency of platelet-activating factor acetylhydrolase is a severity factor for asthma

Abstract

Asthma, a family of airway disorders characterized by airway inflammation, has an increasing incidence worldwide. Platelet-activating factor (PAF) may play a role in the pathophysiology of asthma. Its proinflammatory actions are antagonized by PAF acetylhydrolase. A missense mutation (V279F) in the PAF acetylhydrolase gene results in the complete loss of activity, which occurs in 4% of the Japanese population. We asked if PAF acetylhydrolase deficiency correlates with the incidence and severity of asthma in Japan. We found that the prevalence of PAF acetylhydrolase deficiency is higher in Japanese asthmatics than healthy subjects and that the severity of this syndrome is highest in homozygous-deficient subjects. We conclude that the PAF acetylhydrolase gene is a modulating locus for the severity of asthma.

Figure 1

Distribution of PAF acetylhydrolase activity according to genotype. Plasma samples from control subjects and from asthmatic patients were assayed for PAF acetylhydrolase activity as described previously (29). The genotype at the 279 locus was determined by an allele–specific PCR assay (24), and the subjects were categorized according to genotype. The values reported are the average of two determinations that agreed within 10% of each other.

Figure 2

Distribution of PAF acetylhydrolase activity in normal and asthmatic patients. Plasma samples from control subjects and from asthmatic patients were assayed for PAF acetylhydrolase activity as described (29). The activity values were divided into seven groups of incremental activity and plotted as percentages of the total for each category. The values reported are the average of two determinations that agreed within 10% of each other.

Figure 3

Distribution of PAF acetylhydrolase activity in asthmatic patients based on the genotype at position 279. The PAF acetylhydrolase activity values from asthmatics were categorized according to the genotype at position 279. (The homozygous patients were excluded from this analysis.) The values were divided into seven groups of incremental activity and plotted as percentages of the total for each category. The values reported are the average of two determinations that agreed within 10% of each other.

Figure 4

Distribution of PAF acetylhydrolase activity in white subjects. The plasma PAF acetylhydrolase activity values from white subjects were divided into seven groups of incremental activity and plotted as percentages of the total for each category. The values reported are the average of two determinations that agreed within 10% of each other.

Figure 5

The severity of asthma is dependent on the genotype at position 279. The asthmatic category was divided in four groups according to the severity of the disease. The frequency of individuals with the most severe form of asthma was highest in the homozygous group.

Figure 6

Characterization of an additional mutation (Q281R) that causes partial PAF acetylhydrolase deficiency. (a) The sequence of a mutation found in an asthmatic subject is shown. The Q281R mutation maps near the active site. (b) Immunoblot showing expression of the Q281R mutant in E. coli. (c) PAF acetylhydrolase activity determination of the Q281R mutant protein and its comparison with the wild type and with the vector control.

Figure 7

Sequence of a novel polymorphism in the intron that lies 5′ to exon 12 in the PAF acetylhydrolase gene.

Figure 8

Characterization of a polymorphism (I198T) that has no effect on PAF acetylhydrolase activity. (a) The sequence of a polymorphism found in asthmatic subjects that also harbored the V279F mutation is shown. (b) Immunoblot showing expression of the I198T mutant in E. coli. (c) PAF acetylhydrolase activity determination of the I198T mutant protein and its comparison to the wild type and to the vector control.