Characterization of pre- and post-treatment pathology after enzyme replacement therapy for Pompe disease

In Pompe disease, a genetic deficiency of lysosomal acid alpha-glucosidase, glycogen accumulates abnormally in the lysosomes of skeletal, cardiac and smooth muscle, and contributes to clinically progressive and debilitating muscle weakness. The present study involved 8 infantile-onset Pompe patients, treated weekly with 10 mg/kg of recombinant human acid alpha-glucosidase (rhGAA). Muscle biopsies were obtained at baseline, 12 and 52 weeks post-treatment to establish an indicator of efficacy. Several histologic strategies were employed to characterize changes in pre- and post-treatment samples, including high-resolution light microscopy and digital histomorphometry, electron microscopy, capillary density and fiber type analysis, and confocal microscopy for satellite cell activation analysis. Histomorphometric analysis was performed on muscle samples to assess glycogen depletion in response to enzyme replacement therapy (ERT). The extent of glycogen clearance varied widely among these patient samples, and correlated well with clinical outcome. Low glycogen levels, mild ultrastructural damage, a high proportion of type I fibers, and young age at baseline were all features associated with good histologic response. There was no correlation between capillary density and glycogen clearance, and activated satellite cell levels were shown to be higher in post-treatment biopsies with poor histologic responses. This histopathologic study of infantile Pompe disease provides detailed insight into the cellular progression of the disease and its response to therapy while highlighting a number of methodologies which may be employed to assess regression or progression of the associated pathology. As enzyme replacement therapy becomes more prevalent for the treatment of lysosomal storage diseases, such evaluation of post-treatment pathology will likely become a more common occurrence in the daily practice of pathologists.

Safety and efficacy of rivastigmine in adolescents with Down syndrome: a preliminary 20-week, open-label study

Individuals with Down syndrome (DS) exhibit a cholinergic deficiency similar to that found in Alzheimer's disease. Cholinesterase inhibitors, used to treat Alzheimer's disease, may improve cognitive function in individuals with DS. This is the first investigation of the safety and efficacy of rivastigmine (an acetyl and butyryl cholinesterase inhibitor) on specific cognitive domains in pediatric DS. Eleven subjects with DS (ages 10-17 years) were treated with a liquid formulation of rivastigmine. Four subjects experienced no adverse events (AEs). Seven subjects reported AEs that were mild, transient and consistent with adverse events typically noted with cholinesterase inhibitors. Significant improvements were found in overall adaptive function (Vineland Adaptive Behavior Scales and Clinician's Interview-Based Impression of Change), attention (Leiter Attention Sustained tests A and B), memory (NEPSY: Narrative and Immediate Memory for Names subtests) and language (Test of Verbal Expression and Reasoning and Clinical Evaluation of Language Fundamentals-Preschool) domains. Improved language performance was found across all functional levels. These results underscore the need for larger, controlled studies employing a carefully constructed test battery capable of measuring the full scope of performance across multiple domains and a wide range of functional levels.

Clinical manifestations of hematologic and oncologic disorders in patients with Down syndrome

Hematologic abnormalities are common in individuals with Down syndrome (DS). Increased erythrocyte mean corpuscular volume (MCV) is frequently found among DS infants and remains elevated throughout life in two-thirds of patients, making interpretation of red cell indices for diagnosis of nutritional anemias or bone marrow failure disorders more challenging. Transient myeloproliferative disorder (TMD) associated with pancytopenia, hepatosplenomegaly, and circulating immature WBCs, is found almost exclusively in DS infants with an incidence of approximately 10%. In most cases, TMD regresses spontaneously within the first 3 months of life, but in some children, it can be life threatening or even fatal. Despite the high rate of spontaneous regression, TMD can be a preleukemic disorder in 20-30% of children with DS. The types of malignancy, response to therapy, and clinical outcome in children with DS are also unique. There is an increased risk of leukemia with an equal incidence of lymphoid and myeloid leukemia. Acute megakaryocytic leukemia (AMKL) subtype is the most common form of acute myeloid leukemia (AML) in this setting, and is uncommon in children without DS. Somatic mutations of the gene encoding the hematopoetic growth factor GATA1 have been shown to be specific for TMD and AMKL in children with DS. Myelodysplastic syndrome can precede AML. Children with DS and leukemia are more sensitive to some chemotherapeutic agents such as methotrexate than other children which requires careful monitoring for toxicity. Although the risk for leukemia is higher in individuals with DS, these patients have a lower risk of developing solid tumors, with the exception of germ cell tumors, and perhaps retinoblastoma and lymphoma.

Divergent phenotypes in Gaucher disease implicate the role of modifiers

BACKGROUND

Gaucher disease is classified into neuronopathic and non-neuronopathic forms with wide phenotypic variation among patients sharing the same genotype. While homozygosity for the common L444P allele usually correlates with the neuronopathic forms, how a defined genotype leads to a phenotype remains unknown.

METHODS

The genetic and epigenetic factors causing phenotypic differences were approached by a clinical association study in 32 children homozygous for the point mutation L444P. Direct sequencing and Southern blots were utilised to establish the genotype and exclude recombinant alleles. Glucocerebrosidase activity was measured in lymphoblast and fibroblast cell lines.

RESULTS

Residual enzyme activity was highly variable and did not correlate with the observed clinical course. There was also a wide spectrum of phenotypes. Average age at diagnosis was 15 months, and slowed saccadic eye movements were the most prevalent finding. The most severe systemic complications and highest mortality occurred in splenectomised patients before the advent of enzyme replacement therapy (ERT). On ERT, as morbidity and mortality decreased, developmental and language deficits emerged as a major issue. Some trends related to ethnic background were observed.

CONCLUSION

The wide clinical spectrum observed in the L444P homozygotes implicates the contribution of genetic modifiers in defining the phenotype in Gaucher disease.

Comparison of maltose and acarbose as inhibitors of maltase-glucoamylase activity in assaying acid α-glucosidase activity in dried blood spots for the diagnosis of infantile Pompe disease

PURPOSE

The study's purpose was to compare acarbose and maltose as inhibitors of maltase-glucoamylase activity for determining acid alpha-glucosidase activity in dried blood spot specimens for early identification of patients with infantile Pompe disease, a severe form of acid alpha-glucosidase deficiency.

METHODS

Acid alpha-glucosidase activities in dried blood spot extracts were determined fluorometrically using the artificial substrate 4-methylumbelliferyl-alpha-D-pyranoside. Acarbose or maltose was used to inhibit maltase-glucoamylase, an enzyme present in polymorphonuclear neutrophils that contributes to the total alpha-glucosidase activity at acidic pH.

RESULTS

Complete discrimination between patients with proven infantile Pompe disease (n = 20), obligate heterozygotes (n = 16), and controls (n = 150) was achieved using 8 micromol/L acarbose as the inhibitor. Higher acarbose concentration (80 micromol/L) did not improve the assay. By using 4 mM maltose as the inhibitor, heterozygotes and patients were not completely separated. The results using acarbose compared well with those using the skin fibroblast assay in the same group of patients with proven infantile Pompe disease.

CONCLUSION

Acid alpha-glucosidase activity measurements in dried blood spot extracts can reliably detect infantile Pompe disease in patients. The convenience of collecting and shipping dried blood specimens plus rapid turnaround time makes this assay an attractive alternative to established methods.

A retrospective, multinational, multicenter study on the natural history of infantile-onset Pompe disease

OBJECTIVE

To characterize the natural progression of infantile-onset Pompe disease.

STUDY DESIGN

Retrospective chart reviews of 168 patients with documented acid alpha-glucosidase deficiency and symptom onset by 12 months of age; Kaplan-Meier analysis of total and ventilator-free survival time; Cox proportional hazards regression modeling of mortality risk factors.

RESULTS

The median age at symptom onset was 2.0 months (range 0 to 12 months), 4.7 months at diagnosis (range: prenatal to 4.2 months), 5.9 months at first ventilator support (range 0.1 to 31.1 months), and 8.7 months at death (range 0.3 to 73.4 months). Survival rates at 12 months of age were 25.7% overall and 16.9% ventilator-free; at 18 months 12.3% and 6.7%. Cardiomegaly (92%), hypotonia (88%), cardiomyopathy (88%), respiratory distress (78%), muscle weakness (63%), feeding difficulties (57%), and failure to thrive (53%) appeared after a median age of approximately 4.0 months. Multiple covariate analysis confirmed that early symptom onset increased risk of early death.

CONCLUSION

Despite frequent therapeutic interventions, infantile-onset Pompe disease remains lethal.

Ambulatory electrocardiogram analysis in infants treated with recombinant human acid α-glucosidase enzyme replacement therapy for Pompe disease

PURPOSE

Infantile Pompe disease is caused by deficiency of lysosomal acid alpha-glucosidase. Trials with recombinant human acid alpha-glucosidase enzyme replacement therapy (ERT) show a decrease in left ventricular mass and improved function. We evaluated 24-hour ambulatory electrocardiograms (ECGs) at baseline and during ERT in patients with infantile Pompe disease.

METHODS

Thirty-two ambulatory ECGs were evaluated for 12 patients with infantile Pompe disease from 2003 to 2005. Patients had a median age of 7.4 months (2.9-37.8 months) at initiation of ERT. Ambulatory ECGs were obtained at determined intervals and analyzed.

RESULTS

Significant ectopy was present in 2 of 12 patients. Patient 1 had 211 and 229 premature ventricular contractions (0.2% of heart beats) at baseline and at 11.5 weeks of ERT, respectively. Patient 2 had 10,445 premature ventricular contractions (6.7% of heart beats) at 11 weeks of therapy.

CONCLUSION

Infantile Pompe disease may have preexisting ectopy; it may also develop during the course of ERT. Therefore, routinely monitoring patients using 24-hour ambulatory ECGs is useful. Periods of highest risk may be early in the course of ERT when there is a substantial decrease in left ventricular mass and an initial decrease in ejection fraction.

Electrocardiographic response to enzyme replacement therapy for Pompe disease

PURPOSE

Electrocardiogram (ECG) abnormalities are universal in infantile Pompe disease or glycogen storage disease type II, a fatal genetic muscle disorder caused by deficiency of acid alpha-glucosidase (GAA). Hallmarks of this disease include a shortened PR interval, an increased QT dispersion (QTd), and large left ventricular (LV) voltages. We evaluated the effect of recombinant human GAA (rhGAA) enzyme replacement therapy (ERT) on these ECG parameters in patients with infantile-onset Pompe disease.

METHODS

A total of 134 ECGs were evaluated from 19 patients (5 females and 14 males) with a median age of 5.5 months at the time of enrollment in open-label clinical trials exploring the safety and efficacy of ERT at a single center from 1999 to 2004. rhGAA was purified from genetically engineered Chinese hamster ovary cells overproducing GAA and infused intravenously at doses ranging from 10 mg/kg per week to 20 to 40 mg/kg every 2 weeks in patients with infantile-onset Pompe disease. The PR interval, QTd (longest to shortest QT), and LV voltage (SV1 + RV6) were blindly determined by two independent observers.

RESULTS

The median follow-up period was 6 months (range 2-30 months). The PR interval lengthened from 83 (42-110) ms to 107 (95-130) ms (P < .001), and the QTd decreased from 83 (40-125) ms to 53 (20-80) ms (P = .003). There were significant decreases in LV voltage (67 [17-83] mV vs. 48 [18-77] mV, P = .03), which correlated with decrease in LV mass on two-dimensional echocardiogram. There was no evident change in the QTc interval (429 [390-480] ms vs. 413 [370-450] ms, P = not significant).

CONCLUSION

rhGAA ERT for infantile Pompe disease results in an increase in PR interval and a decrease in both the QTd and the LV voltage. These results suggest that these ECG parameters may be useful markers of the severity of cardiac disease and the response to ERT treatment in patients with infantile Pompe disease.

The use of acarbose inhibition in the measurement of acid alpha-glucosidase activity in blood lymphocytes for the diagnosis of Pompe disease

PURPOSE

Acid alpha-glucosidase is present in various tissues, including blood cells. Historically, enzyme measurement in cultured fibroblasts, or muscle, has been the gold standard to confirm a diagnosis of Pompe disease, due to the possibility of alternate isoenzyme activity masking disease in white cell assays. Enzyme measurement in an isolated lymphocyte population with acarbose, an inhibitor of neutral alpha-glucosidase, has greatly improved the sensitivity and specificity of the test in blood cells allowing for more rapid laboratory testing for Pompe disease.

METHODS

An assay for acid alpha-glucosidase was performed with and without inhibitor in lymphocytes from 14 patients with a clinical suspicion of infantile Pompe disease. Concurrent testing was performed in fibroblasts in an independent laboratory.

RESULTS

Thirteen of 14 patients demonstrated a clear deficiency in lymphocytes with acarbose inhibition. One patient was indeterminate, although below normal activity, suggesting the need for confirmatory testing. Tissue enzyme activity in all was consistent with infantile Pompe disease, and corroborated enzyme activity seen in lymphocytes. There were no false positives for disease, making the positive predictive value of lymphocyte enzyme testing 100%.

CONCLUSION

Enzyme assay using acarbose as an inhibitor, can be performed in isolated lymphocytes for rapid diagnosis of infantile Pompe disease.

Clinical trials in children with Down syndrome: Issues from a cognitive research perspective

Clinical and translational research play a key role in the transition of basic research discoveries to effective therapies. In Down syndrome (DS), these research approaches are not well utilized or developed to test new therapies to improve cognitive and/or adaptive function in this population. This article reviews the history of clinical trial research in children with DS from a cognitive research perspective and discusses important issues relevant to the conduct of well designed clinical trials for this population. Specific issues addressed include: funding, study design, study medication, subject recruitment and retention, safety, and efficacy challenges. The Duke Down Syndrome Research Team's program of clinical research of cholinesterase inhibitors for individuals with DS serves as the model application for the identified research principles. It is hoped that this article will raise awareness of the unmet need for clinical research in the cognitive and adaptive function of individuals with DS, especially children with DS.

Urea Cycle Disorders: Clinical Presentation Outside the Newborn Period

Although most commonly associated with infancy, the majority of individuals with urea cycle disorders (UCDs) present outside the neonatal period, frequently in childhood. Signs and symptoms are often vague, but recurrent; fulminant presentations associated with acute illness are also common. A disorder of urea cycle metabolism should be considered in children who have recurrent symptoms, especially neurologic abnormalities associated with periods of decompensation. Routine laboratory tests, including measurement of plasma ammonia concentrations, can indicate a potential UCD; however, specific metabolic testing and ultimately enzymatic or molecular confirmation are necessary to establish a diagnosis. Treatment with dietary protein restriction and medications may be challenging in children.

Glucose tetrasaccharide as a biomarker for monitoring the therapeutic response to enzyme replacement therapy for Pompe disease

A tetraglucose oligomer, Glcalpha1-6Glcalpha1-4Glcalpha1-4Glc, designated Glc4, has been shown to be a putative biomarker for the diagnosis of Pompe disease. The purpose of this study was to assess whether Glc4 could be used to monitor the therapeutic response to recombinant human acid alpha glucosidase (rhGAA) enzyme replacement therapy (ERT) in patients with Pompe disease. Urinary Glc4 levels in 11 patients receiving rhGAA therapy was determined by both HPLC-UV and stable isotope dilution ESI-MS/MS. Combined Glc4 and maltotetraose, Glcalpha1-4Glcalpha1-4Glcalpha1-4Glc, (M4) concentrations, designated Hex4, in plasma from these patients were measured by HPLC-UV only. Baseline urinary Glc4 and plasma Hex4 in these patients (mean+/-SD: 34.2+/-11.3 mmol/mol creatinine and 1.7+/-0.8 microM, respectively) were higher than age-matched control values (mean+/-SD, 6.1+/-5.1 mmol/mol creatinine and 0.22+/-0.15 microM, respectively). Both urinary Glc4 and plasma Hex4 levels decreased after initiation of ERT for all patients. In the four patients with the best overall clinical response in both skeletal and cardiac muscle, levels decreased to within, or near, normal levels during the first year of treatment. In contrast, levels fluctuated and were persistently elevated above the control ranges in those patients with a less favorable clinical response (good cardiac response but limited motor improvement). These results suggest that urinary Glc4 and plasma Hex4 could serve as a valuable adjunct to clinical endpoints for monitoring the efficacy of therapeutic interventions such as rhGAA ERT in Pompe disease.

Triploid mosaicism in a 45,X/69,XXY infant

We report on an infant referred for chromosome analysis during the neonatal period due to ambiguous genitalia. The genitalia appeared male with bilaterally palpable testes, penoscrotal hypospadias, chordee, and a bifid scrotum. Chromosome analysis and interphase FISH analysis of lymphocytes showed a 45,X karyotype and no evidence for SRY in 200 nuclei examined, respectively. Subsequent chromosome analysis of fibroblasts revealed a 69,XXY karyotype. Molecular studies were carried out to determine the etiology of the chromosome findings. Results indicated that the two cell lines are mosaic rather than chimeric and that the triploidy resulted from delayed dispermy rather than delayed polar body inclusion. To our knowledge this is the first reported living individual with (near) diploid/triploid mosaicism for 45,X/69,XXY.

Hepatocellular carcinoma in glycogen storage disease type Ia: a case series

We present a series of 8 patients (6 males, 2 females) with hepatocellular carcinoma (HCC) and glycogen storage disease type Ia (GSD Ia). In this group, the age at which treatment was initiated ranged from birth to 39 years (mean 9.9 years). All patients but one were noncompliant with treatment. Hepatic masses were first detected at an age range of 13-45 years (mean 28.1 years). Age at diagnosis of HCC ranged from 19 to 49 years (mean 36.9 years). Duration between the diagnosis of liver adenomas and the diagnosis of HCC ranged from 0 to 28 years (mean 8.8 years, SD = 11.5). Two patients had positive hepatitis serologies (one hepatitis B, one hepatitis C). Alpha-fetoprotein (AFP) was normal in 6 of the 8 patients. Carcinoembryonic antigen (CEA) was normal in the 5 patients in which it was measured. Current guidelines recommend abdominal ultrasonography with AFP and CEA levels every 3 months once patients develop hepatic lesions. Abdominal CT or MRI is advised when the lesions are large or poorly defined or are growing larger. We question the reliability of AFP and CEA as markers for HCC in GSD Ia. Aggressive interventional management of masses with rapid growth or poorly defined margins may be necessary to prevent the development of HCC in this patient population.

Benzoate treatment and the glycine index in nonketotic hyperglycinaemia

High-dose benzoate treatment aimed at reducing plasma glycine levels to normal reduces seizures and increases wakefulness in patients with nonketotic hyperglycinaemia (NKH). Since benzoate metabolism is dependent on the available glycine pool, and since the glycine pool is variably affected by the deficiency in the glycine cleavage enzyme system, we examined the importance of interpatient variability in benzoate requirement. To correct for the dietary glycine contribution, the glycine index was introduced as the molar requirement of benzoate dose necessary to normalize plasma glycine levels and subtracting from that the dietary glycine intake, both corrected for weight. The glycine index varied between 3.62 and 4.87 mmol/kg per day in five patients with a poor neurodevelopmental outcome and between 0.92 and 1.90 mmol/kg per day in four patients with a better neurodevelopmental outcome, and was 2.54 mmol/kg per day in a single patient with an intermediate outcome. The glycine index was stable over time within each patient. Exceeding the balance by either increasing food glycine intake or decreasing the benzoate dose resulted in increased glycine levels. Exceeding the glycine tolerance by increasing benzoate resulted in elevated and toxic levels of benzoate. The glycine index is a stable, individually specific parameter in patients with NKH. It has clinical consequences for the dose of benzoate required and the role of dietary management. Through its correlation with neurodevelopmental outcome, the glycine index points to potential genetic factors that could contribute to the psychomotor retardation in NKH.

New onset focal weakness in children with Down syndrome

New onset focal weakness is relatively common in patients with Down syndrome (DS), and has broad differential diagnosis. Ten cases of new onset focal weakness in patients with DS were encountered or are currently being followed in two DS clinics, with a combined population of patients of approximately 850, for a clinic population prevalence of 1.2%. The median age at presentation was 4 years old (range 1 month-44 years). The causes of new onset focal weakness were: stroke from Moyamoya disease (two patients); stroke from vaso occlusive disease (one patient); stroke from venus sinus thrombosis (one patient); traumatic subdural hematoma (one patient); brain abscess (one patient); spinal cord injury (SCI) from cervical spinal stenosis (two patients); SCI from atlantoaxial instability (AAI) (one patient); and brachial plexus injury (one patient). Of the 10 patients with focal weakness, 8 had potentially treatable conditions, and 5 had surgery. The differential diagnosis of new onset focal weakness in DS is broad, with diseases reported involving all levels of the nervous system from brain to muscle. For some diagnoses, expeditious diagnosis may improve outcome.

Anaesthetic management of infants with glycogen storage disease type II: a physiological approach

Pompe or Glycogen Storage Disease type II (GSD-II) is a genetic disorder affecting both cardiac and skeletal muscle. Historically, patients with the infantile form usually die within the first year of life due to cardiac and respiratory failure. Recently a promising enzyme replacement therapy has resulted in improved clinical outcomes and a resurgence of elective anaesthesia for these patients. Understanding the unique cardiac physiology in patients with GSD-II is essential to providing safe general anaesthesia.

Diagnostic and treatment challenges of neuronopathic Gaucher disease: two cases with an intermediate phenotype

Gaucher disease (GD) is a lysosomal storage disorder with a broad, overlapping clinical spectrum. The presented two case reports highlight the clinical evaluation required in neuronopathic GD to assist with medical management and genetic counselling.

Rare disorders of metabolism with elevated butyryl- and isobutyryl-carnitine detected by tandem mass spectrometry newborn screening

Tandem mass spectrometry was adopted for newborn screening by North Carolina in April 1999. Since then, three infants with short-chain acyl-CoA dehydrogenase (SCAD) and one with isobutyryl-CoA dehydrogenase deficiency were detected on the basis of elevated butyrylcarnitine/isobutyrylcarnitine (C4-carnitine) concentrations in newborn blood spots analyzed by tandem mass spectrometry. For three SCAD-deficient infants, biochemical evaluation included a plasma acylcarnitine profile with markedly elevated C4-carnitine, urine organic acid analysis with markedly elevated ethylmalonic and 2-methylsuccinic acids, and markedly elevated [U-13C]butyrylcarnitine concentrations in medium from fibroblasts incubated with [U-13C]palmitic acid and excess l-carnitine, consistent with classic SCAD deficiency. Two of three infants diagnosed with classic SCAD deficiency remained asymptomatic; however, the third infant presented with seizures and a cerebral infarct at 10 wk of age. All three infants had putatively inactivating mutations in both alleles of the SCAD gene. The highly elevated plasma C4-carnitine levels in the three infants detected by newborn screening tandem mass spectrometry differentiated them from infants and children who were homozygous or compound heterozygous for one of two SCAD gene susceptibility variations; for the latter group the C4-carnitine levels were normal. Isobutyryl-CoA dehydrogenase deficiency in a fourth infant was confirmed after isolated elevation of C4-carnitine in the acylcarnitine profile.

Donepezil for the treatment of language deficits in adults with Down syndrome: a preliminary 24-week open trial

At present, there is no proven pharmacologic treatment for cognitive or language impairments in Down syndrome (DS). Cholinergic deficits have been documented in DS and linked to cognitive deficits. This study is a 24-week open-label clinical trial of donepezil hydrochloride for the treatment of language deficits in adults with DS. To our knowledge, this is the first prospective study to evaluate systematically the effects of donepezil, a cholinesterase inhibitor, on specific language domains in DS. The main finding that emerged was an improvement in expressive language performance following donepezil therapy. Despite the multiple methodological limitations, the results raise important questions regarding the role of the cholinergic system in language function and the specific effect of cholinergic therapy in the treatment of language impairment in DS. The results support the need for large-scale controlled studies of the effects of donepezil treatment on language and on other cognitive domains in DS.

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 micromol/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.