Idiopathic Hyperammonemia following an Unrelated Cord Blood Transplant for Mucopolysaccharidosis I

Bone marrow transplantation (BMT) has been shown to reverse or stabilize some manifestations of mucopolysaccharidosis I (Hurler syndrome). Idiopathic hyperammonemia (IHA) is a rare complication of solid organ and BMT that is characterized by elevated serum ammonia, normal liver enzymes, and abrupt onset of neurologic deterioration. We present the case of a 14-month-old male patient with Hurler syndrome who developed fatal IHA (ammonia = 2297 mmol/L) 31 days after a cord blood transplant. A complete autopsy was performed, with examination of both frozen and formalin-fixed paraffin-embedded (FFPE) tissues using a variety of special stains and electron microscopy. Hyperammonemia was documented by analysis of antemortem serum and postmortem cerebrospinal and vitreous fluid. Other causes of hyperammonemia, including Reye syndrome, were excluded. Histologic changes included centrilobular microvesicular steatosis of the liver and storage product present in multiple organs. The highly water-soluble mucopolysaccharide (MPS) storage product was best identified by colloidal iron staining of FFPE and unfixed air-dried fresh frozen liver sections. Alcian blue stains failed to convincingly demonstrate MPS in any of the liver sections. This is the first published report, to our knowledge, of IHA in a posttransplant patient younger than 18 years old or following transplantation for Hurler syndrome. Demonstration of the hepatic centrilobular microvesicular steatosis characteristic of IHA was complicated by the diffuse storage of MPS within the liver. MPS storage can be best detected in the liver using colloidal iron staining. Oil-red-O staining may be useful to document microvesicular steatosis in cases with a clinical history of hyperammonemia following solid organ or BMT. Determining if certain subsets of children are at increased risk for IHA requires further study.