Purine-nucleoside phosphorylase (NP) deficiency is associated with severely defective thymus-derived (T)-cell and normally functioning bone marrow-derived (B)-cell immunity. In this study, two unrelated families with a total of three NP deficient members were investigated.
High pressure liquid chromatography of the plasma of the three patients showed inosine levels greater than 66 μM. This nucleoside was absent from the plasma of their parents and control samples.
NP was purified from normal human erythrocytes by affinity chromatography and an antiserum prepared in rabbits was used to study the NP variants in the two families.
In family M the patient had no detectable erythrocyte NP activity and no detectable immunological-reacting material (irm) to the NP antibody. The parents, who are second cousins, had less than one-half of normal enzyme activity and approximately 14% irm attributable to a variant protein. Their electrophoretic patterns revealed a series of isozymes with slower than normal migration.
In family B the patients had 0.5% residual enzyme activity and about one-half normal irm. Their electrophoretic pattern showed faintly staining bands which migrated faster than normal NP. The mother of the patients had one-half normal enzyme activity, 11% irm attributable to her variant protein, and a normal electrophoretic pattern. The father had less than one-half normal enzyme activity, equal amounts of normal and variant irm, and an electrophoretic pattern that showed increased activity of the more rapidly migrating isozyme bands.
The combined use of immunological and electrophoretic techniques has shown the presence of three separate mutations; one in family M and two in family B associated with severely defective T-cell function.