Considerations in the Difficult-to-Manage Urea Cycle Disorder Patient

Treatment and management for children with urea cycle disorder in chronic stage

Urea cycle disorder (UCD) is a group of inherited metabolic diseases with high disability or fatality rate, which need long-term drug treatment and diet management. Except those with Citrin deficiency or liver transplantation, all pediatric patients require lifelong low protein diet with safe levels of protein intake and adequate energy and lipids supply for their corresponding age; supplementing essential amino acids and protein-free milk are also needed if necessary. The drugs for long-term use include nitrogen scavengers (sodium benzoate, sodium phenylbutyrate, glycerol phenylbutyrate), urea cycle activation/substrate supplementation agents (N-carbamylglutamate, arginine, citrulline), etc. Liver transplantation is recommended for pediatric patients not responding to standard diet and drug treatment, and those with severe progressive liver disease and/or recurrent metabolic decompensations. Gene therapy, stem cell therapy, enzyme therapy and other novel technologies may offer options for treatment in UCD patients. The regular biochemical assessments like blood ammonia, liver function and plasma amino acid profile are needed, and physical growth, intellectual development, nutritional intake should be also evaluated for adjusting treatment in time.

Gas chromatography-mass spectrometry untargeted profiling of non-Hodgkin's lymphoma urinary metabolite markers

Non-Hodgkin's lymphoma (NHL) is a cancer of the lymphatic system where the lymphoid and hematopoietic tissues are infiltrated by malignant neoplasms of B, T, and natural killer lymphocytes. Effective and less invasive methods for NHL screening are urgently needed. Herein, we report an untargeted gas chromatography-mass spectrometry (GC-MS) method to investigate metabolic changes in non-volatile derivatized compounds from urine samples of NHL patients (N = 15) and compare them to healthy controls (N = 34). Uni- and multivariate data analysis showed 18 endogenous metabolites, including amino acids and their metabolites, sugars, small organic acids, and vitamins, as statistically significant for group differentiation. A receiver operating characteristic curve (ROC) generated from a support vector machine (SVM) algorithm-based model achieved 0.998 of predictive accuracy, displaying the potential and relevance of GC-MS-detected urinary non-volatile compounds for predictive purposes. Furthermore, a specific panel of key metabolites was also evaluated, showing similar results. All in all, our results indicate that this robust GC-MS method is an effective screening tool for NHL diagnosis and it is able to highlight different pathways of the disease. Graphical Abstract.

Hyperammonemia Syndrome After Lung Transplantation: A Single Center Experience

BACKGROUND

Hyperammonemia is a rare, often fatal complication after transplantation. The etiology is unknown, but recognition and rapid treatment may help to improve the survival of this unusual syndrome. We present the largest case series to date of hyperammonemia after lung transplantation (LTx) and discuss a treatment protocol that has been developed at our institution.

METHODS

We conducted a retrospective cohort series of patients who underwent LTx between January 1, 2000, and December 31, 2013. Patients who developed hyperammonemia syndrome in the posttransplantation period, which was defined as symptoms of encephalopathy and plasma ammonia level exceeding 200 μmol/L on at least 1 occasion, were included. Data including demographics, antimicrobial and immunosuppression regimens, ammonia levels and other pertinent laboratory data, treatments administered, and outcomes were recorded.

RESULTS

Eight of 807 lung transplant recipients developed hyperammonemia syndrome postoperatively during this time period. Median time to onset was 9.0 days, and median peak ammonia level was 370 μmol/L. All 8 patients were treated with hemodialysis, 7 of 8 patients were treated with bowel decontamination, and 5 of 8 patients were treated with nitrogen scavenging agents. Six of the 8 patients died.

CONCLUSIONS

The incidence of hyperammonemia syndrome in LTx patients was approximately 1%. Future research is needed to determine the efficacy of treatment, including hemodialysis, bowel decontamination, antibiotics, and the use of nitrogen scavenging agents in lung recipients with hyperammonemia.

Single amino acid supplementation in aminoacidopathies: a systematic review

Aminoacidopathies are a group of rare and diverse disorders, caused by the deficiency of an enzyme or transporter involved in amino acid metabolism. For most aminoacidopathies, dietary management is the mainstay of treatment. Such treatment includes severe natural protein restriction, combined with protein substitution with all amino acids except the amino acids prior to the metabolic block and enriched with the amino acid that has become essential by the enzymatic defect. For some aminoacidopathies, supplementation of one or two amino acids, that have not become essential by the enzymatic defect, has been suggested. This so-called single amino acid supplementation can serve different treatment objectives, but evidence is limited. The aim of the present article is to provide a systematic review on the reasons for applications of single amino acid supplementation in aminoacidopathies treated with natural protein restriction and synthetic amino acid mixtures.

Cross-sectional observational study of 208 patients with non-classical urea cycle disorders

Urea cycle disorders (UCDs) are inherited disorders of ammonia detoxification often regarded as mainly of relevance to pediatricians. Based on an increasing number of case studies it has become obvious that a significant number of UCD patients are affected by their disease in a non-classical way: presenting outside the newborn period, following a mild course, presenting with unusual clinical features, or asymptomatic patients with only biochemical signs of a UCD. These patients are surviving into adolescence and adulthood, rendering this group of diseases clinically relevant to adult physicians as well as pediatricians. In preparation for an international workshop we collected data on all patients with non-classical UCDs treated by the participants in 20 European metabolic centres. Information was collected on a cohort of 208 patients 50% of which were ≥ 16 years old. The largest subgroup (121 patients) had X-linked ornithine transcarbamylase deficiency (OTCD) of whom 83 were female and 29% of these were asymptomatic. In index patients, there was a mean delay from first symptoms to diagnosis of 1.6 years. Cognitive impairment was present in 36% of all patients including female OTCD patients (in 31%) and those 41 patients identified presymptomatically following positive newborn screening (in 12%). In conclusion, UCD patients with non-classical clinical presentations require the interest and care of adult physicians and have a high risk of neurological complications. To improve the outcome of UCDs, a greater awareness by health professionals of the importance of hyperammonemia and UCDs, and ultimately avoidance of the still long delay to correctly diagnose the patients, is crucial.

Clinical outcomes of neonatal onset proximal versus distal urea cycle disorders do not differ

OBJECTIVE

To compare the clinical course and outcome of patients diagnosed with one of 4 neonatal-onset urea cycle disorders (UCDs): deficiency of carbamyl phosphate synthase 1 (CPSD), ornithine transcarbamylase (OTCD), argininosuccinate synthase (ASD), or argininosuccinate lyase (ALD).

STUDY DESIGN

Clinical, biochemical, and neuropsychological data from 103 subjects with neonatal-onset UCDs were derived from the Longitudinal Study of Urea Cycle Disorders, an observational protocol of the Urea Cycle Disorders Consortium, one of the Rare Disease Clinical Research Networks.

RESULTS

Some 88% of the subjects presented clinically by age 7 days. Peak ammonia level was 963 μM in patients with proximal UCDs (CPSD or OTCD), compared with 589 μM in ASD and 573 μM in ALD. Roughly 25% of subjects with CPSD or OTCD, 18% of those with ASD, and 67% of those with ALD had a "honeymoon period," defined as the time interval from discharge from initial admission to subsequent admission for hyperammonemia, greater than 1 year. The proportion of patients with a poor outcome (IQ/Developmental Quotient <70) was greatest in ALD (68%), followed by ASD (54%) and CPSD/OTCD (47%). This trend was not significant, but was observed in both patients aged <4 years and those aged ≥ 4 years. Poor cognitive outcome was not correlated with peak ammonia level or duration of initial admission.

CONCLUSION

Neurocognitive outcomes do not differ between patients with proximal UCDs and those with distal UCDs. Factors other than hyperammonemia may contribute to poor neurocognitive outcome in the distal UCDs.

Peptide tyrosine tyrosine levels are increased in patients with urea cycle disorders

Nutritional management is essential for patients with inborn errors of metabolism, such as urea cycle disorders (UCDs). Lack of appetite is common in these patients and can lead to underconsumption of calories, catabolism, and subsequently loss of metabolic control. The etiology of anorexia in these patients is largely unexplored. The neuroendocrine hormone peptide tyrosine tyrosine (PYY), secreted postprandially from endocrine cells of the ileum and colon, induces feelings of satiety and decreases food intake. While plasma PYY levels have been characterized in a number of populations, they have not been examined in UCD patients. In a retrospective study, plasma PYY concentrations were measured in UCD (n=42) patients and controls (n=28) via an ELISA to determine if levels of this anorexigenic hormone are altered in this patient population. Median PYY levels were significantly higher in UCD patients compared to controls (p=3.5×10(-5)). Body mass index was significantly associated with increased PYY levels in controls (p=0.02), while UCD diagnosis subtype was associated with PYY levels (p=1×10(-3)) in cases. Median PYY levels were significantly lower in ornithine carbamoyltransferase deficient patients compared with all other UCD subtypes (p=9×10(-3)), but significantly higher compared to controls (p=1.6×10(-3)). Overall, this study demonstrates that UCD cases have increased PYY levels compared to controls, suggesting that regulation of PYY may be altered in these patients. These observations may lead to a better understanding of the development of anorexia in UCD patients.

Headache and neuropsychic disorders in the puerperium: a case report with suspected deficiency of urea cycle enzymes

An enzymatic abnormality of the urea cycle is a metabolic disorder occasionally seen in adults, but particularly in the puerperium. The main risk is acute hyperammoniemic encephalopathy, leading to psychosis, coma and even death if not diagnosed promptly and treated appropriately. Headache is frequent in the puerperium normally manifesting between 3 and 6 days after delivery. We describe here a 39-year-old woman, who 3 days after delivery presented diffuse tension-type headache and depression, followed by behavioral disorders, psychomotor agitation, epileptic seizures, and finally coma 2 days later. Pregnancy and normal delivery: routine blood chemistry findings, CT scan, MR imaging, angio-MR of the brain, and lumbar puncture were normal. EEG when seizures started, it showed diffuse slowing, as in the case of metabolic encephalopathy. This led us to assay blood ammonia, which was high at >400 mmol. Liver function and abdominal US were normal; hence, we suspected a urea cycle enzymatic abnormality, and requested for genetic tests. These confirmed a congenital primary metabolic deficiency of arginine succinate synthetase, with high citrullinemia (type II, adult form). Dialysis was started promptly, with initially iv arginine, then orally, plus medical therapy for the hyperammoniemia and a low protein diet; plasma ammonia dropped swiftly to normal, and her state of consciousness gradually improved until all the clinical symptoms had resolved. Ammonia assay should always be considered in the first few days of the puerperium in women with headache and behavioral disorders, to exclude an inborn deficiency of the urea cycle, which may have gone unnoticed until then.

Phenylbutyrate improves nitrogen disposal via an alternative pathway without eliciting an increase in protein breakdown and catabolism in control and ornithine transcarbamylase-deficient patients

BACKGROUND

Phenylbutyrate is a drug used in patients with urea cycle disorder to elicit alternative pathways for nitrogen disposal. However, phenylbutyrate administration decreases plasma branched-chain amino acid (BCAA) concentrations, and previous research suggests that phenylbutyrate administration may increase leucine oxidation, which would indicate increased protein degradation and net protein loss.

OBJECTIVE

We investigated the effects of phenylbutyrate administration on whole-body protein metabolism, glutamine, leucine, and urea kinetics in healthy and ornithine transcarbamylase-deficient (OTCD) subjects and the possible benefits of BCAA supplementation during phenylbutyrate therapy.

DESIGN

Seven healthy control and 7 partial-OTCD subjects received either phenylbutyrate or no treatment in a crossover design. In addition, the partial-OTCD and 3 null-OTCD subjects received phenylbutyrate and phenylbutyrate plus BCAA supplementation. A multitracer protocol was used to determine the whole-body fluxes of urea and amino acids of interest.

RESULTS

Phenylbutyrate administration reduced ureagenesis by ≈15% without affecting the fluxes of leucine, tyrosine, phenylalanine, or glutamine and the oxidation of leucine or phenylalanine. The transfer of (15)N from glutamine to urea was reduced by 35%. However, a reduction in plasma concentrations of BCAAs due to phenylbutyrate treatment was observed. BCAA supplementation did not alter the respective baseline fluxes.

CONCLUSIONS

Prolonged phenylbutyrate administration reduced ureagenesis and the transfer of (15)N from glutamine to urea without parallel reductions in glutamine flux and concentration. There were no changes in total-body protein breakdown and amino acid catabolism, which suggests that phenylbutyrate can be used to dispose of nitrogen effectively without adverse effects on body protein economy.

Nutritional management of patients with urea cycle disorders

The nutritional management of patients with urea cycle disorders (UCDs) involves restriction of dietary protein along with provision of adequate protein-free energy, essential amino acid supplements, and vitamins and minerals in combination with nitrogen-scavenging drugs. The present paper discusses nutrition therapy for a range of circumstances: during an acute hyperammonaemic episode and at hospital discharge; before, during, and after surgery; and for lifelong chronic management of UCDs.