To the Editor:
We welcome Drs. Trotter's and Milliner's comments  on our recent publication in the American Journal of Transplantation. We appreciate but respectfully disagree with their conclusion that auxiliary liver transplantation is ineffective or possibly dangerous as a definitive treatment for primary hyperoxaluria (PH). More than 6 years posttransplant, our patient provides evidence that this may still be a reasonable option.
We agree that the metabolic defect in PH is native liver oxalate production, which is caused by hepatocellular alanine glyoxylate aminotransferase (AGT) deficiency. AGT is required to metabolize glyoxylate to glycine. Glyoxylate exists not only primarily in the mitochondrion and the cytosol of the hepatocytes, but also in other cells. Its origin is not well understood, but hydroxyproline from dietary intake  as well as collagen breakdown  are major contributors. Both are extra-hepatic molecules that the auxiliary graft will metabolize. Thus, although the native liver in our patient is still of larger volume than the auxiliary graft, and undoubtedly continues to produce glyoxylate and oxalate, despite the partial portal vein embolization, the recipient's serum and 24-h urine oxalate levels are normalized (most recently 56 mg, compared to 93–240 mg early posttransplant) presumably because of glyoxylate and oxylate uptake by the allograft.
Onaca et al from Baylor  first reported auxiliary liver transplantation correcting serum oxalate in PH1 for up to 1 year in 2005, and now up to 6 years in our report. Our report data and the additional data provided here document the long-term success of this approach in preventing oxaluria and systemic oxalosis, the leading causes for PH1 complications.
The authors'  recommendation that total hepatectomy is needed is supported by dated articles and textbooks, which, however, do not reference failure of auxiliary liver transplantation per se, but rather a theoretical conclusion of hepatocyte transplantation failure . This is not surprising given our findings. It appears critical to provide sufficient hepatocyte mass to metabolize the circulating glyoxylate and oxalate produced by the native liver. Total hepatectomy and transplantation is obviously also effective and technically simpler. However, this approach still provides a lower survival rate in these patients compared to the national average of liver transplant recipients , and contributes to the donor organ shortage. For these reasons we think total hepatectomy for PH should be discontinued.
Also, very important, the right tri-segment of the donor liver was transplanted to a second recipient. The disparity between demand and supply of donor allografts remains the primary limitation of liver transplantation , especially in Region 1. We therefore advocate against using a whole liver for transplant in this metabolic disorder, thereby maximizing benefit to our waitlisted population with every single deceased donor liver.
N. Elias*, A. B. Cosimi and M. Hertl
Massachusetts General Hospital, Boston, MA
*Corresponding author: Nahel Elias, Elias.Nahel@MGH.Harvard.edu