Identification of Patients With High Probability of Poorly Responding to Therapy With Mycophenolic Acid Prodrugs

This study is designed to define groups of patients (among patients with a heart or kidney graft or a glomerular disease and nephrotic range proteinuria) who would either not profit from a therapy with mycophenolate-mofetil (MMF) or need a higher than conventional dose to respond.

Mainly there are 2 possible explanations for inter-patient differences in responsiveness to MMF therapy:

1. Based on a mutation (in this study single nucleotide polymorphisms-SNPs-) in the inosine monophosphate dehydrogenase 2 (IMPDH 2) transcript as the target enzyme of mycophenolic acid (MPA) pathway, MMF cannot exert its effect. 2. Based on a high enzyme activity of IMPDH 2 a higher MMF dose than in the conventional regimens is needed.

To study the significance of these possible explanations there are 4 objectives in this study:

Objective 1: Since there are no data on SNPs with functional relevance in IMPDH 2 transcript, we will first sequence all 14 exons of this gene in their entirety in 100 gender and age matched healthy individuals.

Objective 2: The functional relevance of a detected SNP will be tested in vitro in a lymphocyte proliferation assay using various MPA concentrations.

Objective 3: These functionally relevant SNPs will be searched in patients with kidney graft in a retrospective as well as prospective manner.

Objective 4: Parallel to the genotyping experiments, IMPDH 2 activity and MPA plasma levels will be measured in all patients recruited in the study prospectively.

An association between these SNPs or various IMPDH 2 activity / MPA plasma levels with MMF responsiveness will be examined.

Objective 5: Strongyloides IgG titers are screened to evaluate the prevalence of helminth carriers in patients with immunosuppressive therapy.