878. Correction of Maternal Phenylketonuria Syndrome in the Pahenu2 Missense Mutant Mouse by r-AAV Mediated Gene Therapy

Abstract

The current treatment for Phenylketonuria (PKU) is strict, lifelong, restriction of phenylalanine (Phe) in the diet. While the deleterious effects of PKU are alleviated by diet, patient compliance, especially in adults, can be poor. A second problem is the rise in Maternal PKU Syndrome, the greatly increased incidence of neurological damage in the offspring of PKU mothers who were unable to maintain good physiological control of Phe levels during pregnancy. We have previously reported long-term therapeutic correction of serum Phe levels in the Pahenu2 BTBR mouse model of PKU, using recombinant Type 2 Adeno Associated Virus vectors carrying the mouse phenylalanine hydroxylase gene (rAAV-mPAH). A second rAAV-mPAH vector now contains the WPRE element (rAAV-mPAH-WPRE). Portal vein injection of this vector into male Pahenu2 mice lowered serum phe to therapeutic levels (<0.5 μM) at 10-fold lower doses than vectors lacking the WPRE element. WPRE-containing vectors were able to lower serum Phe levels to physiological levels (0.05-0.1 μM) at vector doses of 2.5 × 1010 I.U. However, as previously reported, female PKU mice were unresponsive to doses effective in males, although a therapeutic reduction is now seen with rAAV-mPAH-WPRE vector doses of 1.5 × 1011 I.U. The presence of a dominant-negative interaction between normal subunits of the PAH tetramer made from the vector-delivered gene and the endogenous PAH missense subunits is a possible explanation of these results (See abstract by Charron et.al.). The relative inefficiency of rAAV gene therapy in treating the Pahenu2 mouse emphasizes the importance of examining the full spectrum of natural (missense as well as null) mutations to evaluate the effectiveness of gene therapy for treating human genetic disease.