Purine nucleoside phosphorylase (
PNP) deficiency is an immunodeficiency disorder characterized by
recurrent infections,
failure to thrive and neurologic symptomatology. While
enzyme replacement therapy (ERT) is a therapeutic option for
adenine deaminase (
ADA) deficiency, a similar disorder, this is not available for
PNP deficiency, and bone marrow transplant (BMT) is the only treatment option. Moreover, even with BMT, improvement of neurological deficits is not definite. We describe a 16-month-old boy who underwent BMT for
PNP deficiency which resulted not only in freedom from
infections but also in neurological improvement and autologous T-cell recovery.Pre-transplant, this child had severe
lymphopenia with
recurrent infections and psychomotor retardation. Post-transplant, in the presence of mixed chimerism, he had normal lymphocyte count, including presence of recipient T cells and neurological improvement. The re-emergence of recipient T cells, when there were virtually no such cells pre-transplant, and the neurological improvement are indicative of improvement of the
enzyme deficiency in tissues which remain genetically
enzyme depleted.These defects are not directly corrected by BMT, but are due to delivery of the missing
enzyme by the transplanted tissue. In this aspect,
transplantation in
PNP deficiency is similar to
transplantation in other
inborn errors of metabolism where the engrafted donor cells deliver
enzyme and restore function to deficient tissues. This further lends support to the recommendations that BMT should be the favoured treatment option in disorders like
ADA deficiency or
Hurler syndrome, where, even though ERT is available, it is limited by inability to correct the central nervous system defects.