The hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome (OMIM#238970) (1) is a rare autosomal recessive disorder caused by defective activity of the mitochondrial transporter of ornithine across the inner mitochondrial membrane (2). The carrier defect results in cytoplasmic ornithine accumulation with intramitochondrial ornithine depletion, causing a secondary urea cycle defect and consequent elevation of plasma ammonia. Mutations in the solute carrier gene SLC25A15, encoding the ornithine transporter ORNT1, have been detected in patients with HHH syndrome (3). The clinical manifestations and the age at onset of the syndrome are highly variable, ranging from protein-rich food intolerance, vomiting, and neurological signs such as lethargy, coma, seizures, progressive spastic paraparesis, and mental retardation (4,5). Moderate liver involvement has been described in several patients. Recently Fecarotta et al (6) reported a patient with HHH syndrome who presented with fulminant liver failure and coagulopathy. The molecular characterization of this patient showed two novel mutations in the SLC25A15 gene. We report on two patients presenting with acute hepatic failure in whom the diagnosis of HHH was established. Both were homozygous for the common French Canadian mutation (F188Δ) in the SLC25A15 gene (3). Rapid diagnosis allowed for timely treatment and avoidance of liver transplant in both.
Patient 1 was born at term to a healthy 31-year-old gravida 5 para 4 mother by spontaneous vaginal delivery. The pregnancy history was unremarkable, with no history of exposure to known teratogens. There were no perinatal complications. She was born to an Aboriginal couple who were first cousins. She had four healthy siblings. Her developmental history was age appropriate. She was thriving very well with regular formula and was eating solids. There was no history of aversion to protein-rich foods. Her past medical history was unremarkable.
At 12 months of age, she was referred to our center with a diagnosis of febrile seizures after a 2-day history of fever and cough. She was given antibiotics for the treatment of right lower lobe pneumonia. Her ammonia on admission was normal at 53 μmol/L (normal 33–67 μmol/L) (Table 1). Her initial liver function tests revealed marked elevation of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and moderate elevation of gamma glutamyl transaminase (GGT) (Table 1). Physical examination showed no signs of encephalopathy, hepatomegaly, or jaundice.
Her clinical course was characterized in the ensuing 7 days by rapidly progressing severe hypertransaminasemia (AST and ALT peaking at 19186 UI/L and 12760 UI/L, respectively) on day 6 (Table 1) and severe coagulopathy: prothrombin time (PT) of 59 seconds (normal 11.3–13.3), activated partial thromboplastin time of 83 seconds (normal 26–34), international normalized ratio (INR) of 7.6 (normal 0.8–1.3). Coagulation factor assays revealed very low activity of the following: factor II, 13% (normal 50%–150%); factor V, 38% (normal 50%–150%); factor VII, <4% (normal 50%–150%); factor IX, 3% (50%–150%); and factor X, 13% (50%–150%). Fibrinogen and factor VIII were normal. Serum albumin and bilirubin remained within the normal range. The coagulopathy did not respond to parenteral vitamin K therapy.
Plasma ammonia on day 6 was elevated at 139 μmol/L, and the child was noted to be lethargic. The results of further metabolic tests became available on day 6 and showed elevated blood concentrations of ornithine, 933 μmol/L (normal 40–160), and homocitrullinuria, 456 μmol/L (normal 5.3–175). Urine orotic acid was not measured.
Owing to the presence of hyperammonemia, hyperornithinemia, and homocitrullinuria, a diagnosis of HHH syndrome was proposed. Management with intravenous L-arginine supplementation (250 mg/kg/24 h), 20% Intralipid (2 g/kg/24 h), and dextrose intravenously was commenced. Initially, protein intake was completely restricted. On the basis of the clinical and biochemical data suggestive of acute liver failure, the patient was transferred to a liver transplant center for emergent liver transplant assessment should she not respond to medical management.
After approximately 24 hours of this regimen, her blood ammonia normalized. A rapid improvement of the hypertransaminasemia was observed over the first 72 hours of therapy (Table 1). Owing to the rapid response to medical therapy and the correction of biochemical abnormalities, the need for urgent liver transplantation was obviated. The infant was referred back to our center, from where she was discharged to receive long-term therapy with oral L-arginine supplementation (250 mg/kg/day) and protein restriction to meet her recommended nutrient intake of 1 g/kg/day. Half of her protein intake was through Cyclinex-1 formula, and the rest was from natural sources. There has been no further metabolic dysfunction to date, and her liver function has remained normal (Table 1).
Because of the patient's ethnic background, molecular analysis for the SLC25A15 F188Δ mutation, which is found commonly in patients of French Canadian descent (3), was performed. The patient was found to be homozygous for this deletion.
Patient 2 was a 15 month-old Aboriginal girl born after an uneventful pregnancy by spontaneous vaginal delivery. Cleft lip and palate were noted at birth. There was a history of developmental delay and moderate hypotonia. She was not walking or standing and was babbling but had no words. She had no history of seizures or abnormal movements. She was drinking a soy formula but refusing solid foods. She was seen by a medical geneticist, and her karyotype was normal. There was no family history of liver or metabolic diseases. The parents were both Aboriginal, and there was no known consanguinity.
A cleft lip repair was performed when the patient was 4 months old, with no complications. Prolonged bleeding after the cleft palate repair at age 15 months was noted, prompting further investigations, which revealed that the INR was 5.4 and activated partial thromboplastin time was 88 seconds. Coagulation factor assays revealed very low activity of the following: factor II, 0.27 g/L (normal 0.5–1.5); factor V, 0.16 g/L (normal 0.5–1.5); factor VII, 0.04 g/L (0.5–1.5); factor IX, 0.04 g/L (0.5–1.5); and factor X, 0.22 g/L (0.5–1.5). Fibrinogen and factor VIII were normal. Liver enzymes were significantly elevated, with ALT at 900 U/L and aspartate aminotransferase (AST) at 968 U/L. Plasma ammonia was elevated (98 μmol/L) (Table 2). GGT, alkaline phosphatase, and bilirubin were all normal, and there was no hypoglycemia. Her coagulopathy was not correctable with multiple doses of vitamin K. Clinically she remained well, showing no signs of encephalopathy, jaundice, or hepatomegaly. The results of liver biopsy were normal, with no evidence of hepatic necrosis on microscopy.
With these biochemical findings of liver failure, further investigations were done, including blood gas determination, which revealed no evidence of metabolic acidosis or alkalosis. Quantitative amino acid analysis revealed an elevated ornithine at 580 μmol/L (normal 40–160). Urine organic and amino acid analyses revealed the presence of orotic acid and homocitrulline. Mutational analysis revealed that she was homozygous for the common French Canadian mutation F188Δ in the ORNT1 gene. A diagnosis of HHH syndrome was therefore confirmed. She was transferred to a liver transplant center for liver transplant assessment during the acute phase of her illness in the event that she continued to deteriorate, necessitating a liver transplant.
A protein-restricted diet was initiated, and L-citrulline was started at a dosage of 250 mg/kg/day. There was and continues to be an excellent response to medical treatment with Cyclinex-1 formula and L-citrulline, obviating the need for transplant. Liver transaminases and coagulation factors all normalized. Ammonia and glutamine normalized, and urine orotic acid decreased significantly.
It is crucial to include inborn errors of metabolism, including HHH, in the differential diagnosis of patients with acute rapidly progressive liver disease. A high index of suspicion allows for early identification and treatment of these patients and can be life saving. HHH syndrome presenting with severe liver failure has been reported only once previously, to our knowledge (6). A 3-year-old Italian patient with HHH syndrome experienced severe liver failure, presumably due to hepatocellular necrosis with hypertransaminasemia (aspartate aminotransferase 20,000 UI/L, alanine aminotransferase 18,400 UI/L) and coagulopathy, prompting evaluation for liver transplantation. The patient's liver dysfunction improved with a protein-restricted diet and arginine supplementation. Molecular analysis of the SLC25A15 gene showed that the patient was compound heterozygous for two novel mutations (G113C and M273K).
There are several reports in the HHH literature of milder liver involvement, sometimes in association with mild coagulopathy and reduced clotting factors VII and X. The original patient reported by Shih et al (7) presented with a moderate increase of AST level. There was no evidence of hepatomegaly or coagulation abnormality. Dionisi Vici et al (8) reported 2 patients with hypertransaminasemia, one of whom showed deficiency of clotting factors VII and X. Smith et al (9) reported a patient with slightly prolonged partial thromboplastin time, normal prothrombin time, defect of several clotting factors, and a mild abnormality of liver function test results (both below 200 U/L) first discovered during a preoperative evaluation for tonsillectomy. In all reported cases, liver involvement was mild. Our patients' acute hepatic dysfunction is consistent with a fulminant hepatitis-like presentation, more similar to that in the patient reported by Fecarotta et al (6).
Molecular data do not help explain the clinical variability in HHH syndrome, and no genotype-phenotype correlation in this disorder has been reported, with most identified mutations being private. The finding of a different mutation from ours in the patient presenting with acute hepatic insufficiency reported by Fecarotta et al (6) similarly supports the lack of genotype-phenotype correlation in this disorder. Patient 2 is from a remote community in northern Saskatchewan, where HHH is known to be overrepresented (10). In the eight patients from northern Saskatchewan identified to date, either clinically or through newborn screening, there is marked interfamilial and intrafamilial clinical variability. Some patients have remained entirely asymptomatic, receiving either no treatment or mild protein restriction. This is the first known patient with HHH from this high-risk area to present with acute liver dysfunction. This clinical variability suggests the existence of either modifying genes or different environmental factors. Patient 1 is from a geographically isolated community in northern Manitoba but with common ancestry to the community of patient 2. HHH has not been previously identified in the community of patient 1. Both patients are homozygous for the common mutation seen in French Canadian patients from Quebec and our hypothesis pending haplotype analysis is that there is a common founder mutation.
Severe and progressive liver failure in our patients required a prompt diagnosis of the underlying cause and also rapid decisions about treatment strategies. Liver transplantation was considered in both patients because of their rapidly deteriorating liver profiles. A prompt diagnosis of HHH syndrome proved of great importance in instituting appropriate treatment. Protein-restricted diet with Cyclinex-1 and L-arginine or L-citrulline supplementation proved effective in reversing all biochemical abnormalities and avoiding the need for liver transplantation in both patients.
The mechanism of liver failure remains unknown and seems less likely to be due to massive hepatic necrosis, as supported by the normal bilirubin and albumin levels in previously reported patients and ours. The liver biopsy in our second patient did not show any signs of hepatic necrosis. We speculate that mitochondrial dysfunction in HHH syndrome gives rise to hepatocyte injury resulting in hypertransaminasemia and affecting clotting factor synthesis, resulting in severe coagulopathy but sparing the biliary tree.
The authors thank the following for their assistance: the metabolic laboratory and consulting physicians Drs S. Moroz, F. Booth, N. Shah, and R. Yanofsky; clinical dietician D. Weiten in Winnipeg; gastroenterology fellow Dr M. Turaiki in Edmonton; and consulting physicians Drs C. Prasad and P. Atkison in London, Ontario.
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