A pilot study of neonatal GALT gene replacement using AAV9 dramatically lowers galactose metabolites in blood, liver, and brain and minimizes cataracts in GALT-null rat pups

Abstract

Classic galactosemia (CG) is a rare metabolic disorder that results from profound deficiency of galactose-1-P uridylyltransferase (GALT). Despite early detection by newborn screening and rapid and lifelong dietary restriction of galactose, which is the current standard of care, most patients grow to experience a broad constellation of long-term complications. The mechanisms underlying these complications remain unclear and likely differ by tissue. Here we conducted a pilot study testing the safety and efficacy of GALT gene replacement using our recently-described GALT-null rat model for CG. Specifically, we administered AAV9.CMV.HA-hGALT to seven GALT-null rat pups via tail vein injection on day 3 of life; eight GALT-null pups injected with PBS served as the negative control, and four GALT+ heterozygous pups injected with PBS served as the positive control. All pups were returned to their nursing mothers, weighed daily, and euthanized for tissue collection 2 weeks later. Among the AAV9-injected pups in this study, we achieved GALT levels in liver ranging from 64% to 595% wild-type, and in brain ranging from 3% to 42% wild-type. In liver, brain, and blood samples from these animals we also saw a striking drop in galactose, galactitol, and gal-1P. Finally, all treated GALT-null pups showed dramatic improvement in cataracts relative to their mock-treated counterparts. Combined, these results demonstrate that GALT restoration in both liver and brain of GALT-null rats by neonatal tail vein administration using AAV9 is not only attainable but effective.

Keywords: AAV9; GALT; galactosemia; gene therapy; metabolite; rat.

Figure 1:. The Leloir pathway of galactose metabolism.

Classic galactosemia (CG) results from profound deficiency of galactose-1-P uridylyltransferase (GALT). The 3 metabolites followed in this study (galactose, galactitol, and gal-1P) are boxed in this figure.

Figure 2:. Metabolic impact of restored GALT activity in GALT-null rat pups.

Expression of an hGALT transgene in GALT-null pups normalized, or near-normalized, galactose, galactitol, and gal-1P in all samples tested including plasma, RBC, liver, and brain.

Figure 3:. Restored GALT activity minimized cataracts in GALT-null rat pups.

As a group, the 7 GALT-null pups treated with AAV9-hGALT in this study demonstrated clear improvement of cataracts relative to their mock-treated counterparts.