Early intervention for late-onset ornithine transcarbamylase deficiency

Diagnostic and Management Issues in Patients with Late-Onset Ornithine Transcarbamylase Deficiency

Ornithine transcarbamylase deficiency (OTCD) is the most common inherited disorder of the urea cycle and, in general, is transmitted as an X-linked recessive trait. Defects in the OTC gene cause an impairment in ureagenesis, resulting in hyperammonemia, which is a direct cause of brain damage and death. Patients with late-onset OTCD can develop symptoms from infancy to later childhood, adolescence or adulthood. Clinical manifestations of adults with OTCD vary in acuity. Clinical symptoms can be aggravated by metabolic stressors or the presence of a catabolic state, or due to increased demands upon the urea. A prompt diagnosis and relevant biochemical and genetic investigations allow the rapid introduction of the right treatment and prevent long-term complications and mortality. This narrative review outlines challenges in diagnosing and managing patients with late-onset OTCD.

A complex case of delayed diagnosis of ornithine transcarbamylase deficiency in an adult patient with multiple comorbidities

We report the case of a medically complex African American adult female with ornithine transcarbamylase (OTC) deficiency diagnosed after lifelong protein aversion and new onset of chronic vomiting and abdominal pain with intermittent lethargy and confusion. Symptomatology was crucial to diagnosis as genetic testing did not identify any pathogenic variants in OTC; however, the patient's diagnosis was delayed despite her having longstanding symptoms of a urea cycle disorder (UCD). Her symptoms improved after treatment with a modified protein-restricted diet, long-term nitrogen-scavenger therapy, and supplemental L-citrulline. Adherence to her UCD management regimen remained a challenge due to her underlying frailty and other medical conditions, which included primary renal impairment (further exasperated by type 2 diabetes mellitus) and decreased left-ventricular function. She passed away 3 years after her OTC deficiency diagnosis due to complications of congestive heart failure. Her OTC deficiency did not have a major impact on her final illness, and appropriate OTC deficiency management was provided until the decision was made to withdraw medical care.

Benefits of tailored disease management in improving tremor, white matter hyperintensities, and liver enzymes in a child with heterozygous X-linked ornithine transcarbamylase deficiency

We report the case of a 19-month-old girl with late-onset ornithine transcarbamylase (OTC) deficiency initially referred to gastroenterology for intermittent vomiting lasting a year and abnormal liver enzymes (AST 730 U/L [reference range 26-55 U/L]; ALT 1213 U/L [reference range 11-30 U/L]) without hepatomegaly. While the patient was hospitalized for liver biopsy, intermittent tremors of the upper extremities with varying severity were noted. The patient was presumed to have hyperammonemia secondary to acute liver failure and was discharged after 5 days; follow-up monitoring led to readmission 7 days later. A brain MRI showed nonspecific bilateral pericallosal and bifrontal white matter FLAIR hyperintensities. These findings raised suspicion for a metabolic disease and prompted a genetics consultation. After inconclusive biochemical testing and worsening clinical status, rapid whole genome sequencing results were obtained identifying a novel, de novo, likely pathogenic, variant c.608C > T (p.Ser203Phe) in the OTC gene. The patient was promptly started on an oral nitrogen scavenger, citrulline supplementation, and protein restriction. Ammonia and glutamine levels normalized within 1 month of treatment and have stayed within the goal ranges with continued tailoring of treatment. Her parents noted resolution of vomiting and improved mood stability. Liver enzymes normalized after 2 months of treatment. The tremor, identified as asterixis, improved and a repeat brain MRI 3 months after the initial imaging showed near-complete resolution of previous white matter hyperintensities.

Case Report: Juvenile Myelomonocytic Leukemia Underlying Ornithine Transcarbamylase Deficiency Safely Treated Using Hematopoietic Stem Cell Transplantation

BACKGROUND

Juvenile myelomonocytic leukemia (JMML), which is predominantly found in infants, is a clonal abnormality of pluripotent hematopoietic stem cells and presents with the symptoms of both myeloproliferative tumors and myelodysplastic syndromes. Estimates have shown that ~20 cases of JMML occur annually in Japan. Ornithine transcarbamylase deficiency (OTCD), the most common among all urea cycle disorders (UCDs), occurs in 1 of 80,000 people in Japan.

CASE PRESENTATION

A 10-month-old infant who had fever, vomiting, and diarrhea for 2 days was referred to our hospital for the following abnormalities in blood tests: white blood cell count, 48,200/μL; hemoglobin, 9.0 g/dL; and platelet count, 135,000/μL. Bone marrow examination showed a nucleated cell count of 396,000/mm³ and blast cell count of 5.0%, as well as decreased mature granulocyte count and slightly myeloperoxidase stain-negative blasts but no monoclonal cell proliferation on May-Giemsa staining. Colony assay showed the proliferation of spontaneous colony and high sensitivity to granulocyte-macrophage colony-stimulating factor. Genetic analysis of peripheral blood mononuclear cells showed that the patient was positive for neuroblastoma RAS (NRAS) mutation. The patient was ultimately diagnosed with JMML. Approximately 170 days after his first hematopoietic stem cell transplantation (HSCT), the patient's JMML relapsed. Shortly after the recurrence, nausea, vomiting, hyperventilation, and decreased vitality were observed, followed by a decrease in the level of consciousness. The patient's ammonia level was 472 μmol/L. A test for seven different genetic mutations for the UCD showed the presence of c. 119G>A (amino acid change p. Arg40His). As such, late-onset OTCD was added to his diagnosis. Administration of sodium phenylacetate, l-arginine hydrochloride, and carnitine was continued following the diagnosis of OTCD, after which hyperammonemia was not observed. Regarding JMML relapse, HSCT was performed on day 405 after the first transplantation.

CONCLUSION

Hyperammonemia should be considered a differential diagnosis when unexplained and non-specific symptoms occur during the treatment of hematologic malignancies. Patients should be tested for UCD as a cause of hyperammonemia, and treatment for hyperammonemia should be continued until the cause is identified. The patient shows normal developmental progress, has an intact neurological status, and has not experienced another hyperammonemia attack. His JMML has remained in remission for over 3 years.

An Introduction to Pharmacotherapy for Inborn Errors of Metabolism

Inborn errors of metabolism comprise a wide array of diseases and complications in the pediatric patient. The rarity of these disorders limits the ability to conduct and review robust literature regarding the disease states, mechanisms of dysfunction, treatments, and outcomes. Often, treatment plans will be based on the pathophysiology associated with the disorder and theoretical agents that may be involved in the metabolic process. Medication therapies usually consist of natural or herbal products. Established efficacious pediatric doses for these products are difficult to find in tertiary resources, and adverse effects are routinely limited to single case reports. This review article attempts to summarize some of the more common inborn errors of metabolism in a manner that is applicable to pharmacists who will provide care for these patients.