Intrafamilial phenotypic variability in citrullinaemia: report of a family

Hyperammonemic Encephalopathy in an Adolescent Patient of Citrullinemia Type 1 With an Atypical Presentation

Citrullinemia refers to a family of autosomal recessive disorders involving the urea cycle. Three forms exist, which have different implications. Type I citrullinemia exists in both mild and severe forms. It arises due to mutations with argininosuccinate synthase leading to accumulation of ammonia and producing symptoms of lethargy, poor feeding, and seizures. Type II citrullinemia occurs due to citrin mutations involved in the urea cycle transport or during neonatal cholestasis. Management of both conditions requires low-protein diets along with arginine, sodium benzoate, and sodium phenylacetate. While traditional treatment shows improved outcomes, modifications may be necessary depending on a patient’s presentation.

We present a unique case of a 19-year-old wheelchair-bound female with a past medical history of heterozygous type I citrullinemia, seizures, and chronic encephalopathy presented to a local children’s hospital for evaluation of altered mental status with a lethargic mental state. She was initially found to have an ammonia level of 329 µmol/L and choledocholithiasis on admission. Dietary modification with intravenous dextrose and intralipids with oral lactulose saw improvement in her labs. However, her ammonia level increased to 381 µmol/L despite such interventions. Intensive care was required to normalize her serum ammonia level and clear her for a magnetic resonance cholangiopancreatography (MRCP).

We present a unique case of heterozygous type I citrullinemia with some overlap with type II citrullinemia features. Further studies are needed to understand better the observed unique presentation and long-term clinical implications associated with the disease.

30-year follow-up of a patient with classic citrullinemia

Citrullinemia is a urea cycle defect requiring long-term care with nutritional and pharmacological management. Despite treatment, morbidity and mortality of this disease remain high, and long-term complications include mild to profound mental retardation, seizures, and growth deficiency. We report a 31-year old woman with classic, neonatal-onset citrullinemia who developed progressive hypertrophic cardiomyopathy and cataracts, neither of which has been recognized previously as a complication of the disease or a consequence of long-term drug treatment.

Favorable long-term outcome following severe neonatal hyperammonemic coma in a patient with argininosuccinate synthetase deficiency

This chapter reports on the sequelae-free 8-year follow-up with normal growth, intellectual development, and schooling of a boy with argininosuccinate synthetase deficiency (citrullinemia type I) who was rescued from severe neonatal hyperammonemic coma at 8 days of life (peak ammonia level of 1,058 μmol/L). Important clinical management aspects were: rapidity of response to emergency therapeutic measures that included specific drug regimen, protein restriction, optimal caloric intake and hemodialysis, short coma duration (14 h), possible neuroprotective effect of mild systemic hypothermia during the acute episode, long-term metabolic control with strict compliance to standard of care therapeutic and dietary regimens, active prevention of subsequent hyperammonemic episodes, and early neurodevelopmental evaluations and interventions. We conclude that good long-term neurological outcome following rescue from neonatal hyperammonemic coma is rarely reported but attainable. Prospective registries and interventional studies regrouping clinical data from urea cycle disorders patients will assist clinicians in instituting the appropriate therapeutic measures to provide the best prospect of positive long-term outcome for these children.

Pregnancy in a healthy woman with untreated citrullinemia

We report the clinical and biochemical data on a second successful pregnancy in a woman with citrullinemia due to argininosuccinate synthetase deficiency (CTLN1). Despite very elevated plasma and urine citrulline and little or no measurable argininosuccinate synthetase enzyme activity on cultured skin fibroblasts, this 29-year-old woman, who was identified through newborn screening, has remained asymptomatic throughout her life. Mutation analysis has recently revealed that she is a compound heterozygote for a known and a novel mutation (IVS15-1G > C and K310Q, respectively). Many newborn screening programs have recently been expanded to include citrullinemia and numerous asymptomatic hypercitrullinemic infants and children have been identified. It is now important to define prognostic indicators that will help with treatment decisions and genetic counseling for these patients. This patient, as the only citrullinemic adult who has been followed prospectively, contributes important information in this regard. In addition, her child was unaffected by the high citrulline levels demonstrated in amniotic fluid and breast milk suggesting that citrulline is not teratogenic. Although pregnancy is an important risk factor for women with CTLN1, it appears that females with citrullinemia can have normal pregnancy outcomes, as long as metabolic crisis is avoided.

Poly(ethylene glycol) (PEG) conjugated arginine deiminase: effects of PEG formulations on its pharmacological properties

Some tumors, such as melanomas and hepatocellular carcinomas, have a unique nutritional requirement for arginine. Thus, enzymatic degradation of extracellular arginine is one possible means for inhibiting these tumors. Arginine deiminase is an arginine degrading enzyme (ADI) that has been studied as an anti-cancer enzyme. However, ADI has a short serum half-life and, as a microbial enzyme, is highly immunogenic. Formulation of other therapeutic proteins with poly(ethylene glycol) (PEG) has overcome these problems. Here, ADI-PEGs were synthesized using PEGs of varying size, structure (linear or branched chain) and linker chemistries. All ADI-PEGs retained approximately 50% of enzyme activity when PEG was covalently attached to approximately 40% of the primary amines irrespective of the PEG molecular weight or attachment chemistry used. However, it was observed that, as the PEG size increases to 20 kDa, there was a corresponding increase in the pharmacokinetic (pK) and pharmacodynamic (pD) properties of the formulation. Variation in PEG linker or structure, or the use of PEGs >20,000 mw, did not affect the pK or pD. As has been shown with other therapeutic proteins, repeated injection of ADI-PEG into experimental animals resulted in significantly lower titers of antibodies against this protein than unmodified ADI. These data suggest that formulation of ADI with PEG of 20,000 mw results is the optimal method for formulating this promising therapeutic agent.

Case report: recurrent hyperammonaemic encephalopathy due to citrullinaemia in a 52 year old man

The present report describes a Chinese male who presented for the first time with recurrent encephalopathy and hyperammonaemia at the age of 52 years. He was found to have citrullinaemia. To our knowledge, this is the first Chinese with citrullinaemia and the first non-Japanese who has the variant form of presentation. The patient also has the longest asymptomatic period for citrullinaemia so far described. The patient's biochemical derangement, clinical features and the postulation of his late presentation are discussed. It is noteworthy that simple therapeutic measures, such as lactulose and dietary protein restriction, controlled his symptoms well.

Autosomal recessive disorders among Arabs: an overview from Kuwait

Kuwait has a cosmopolitan population of 1.7 million, mostly Arabs. This population is a mosaic of large and small minorities representing most Arab communities. In general, Kuwait's population is characterized by a rapid rate of growth, large family size, high rates of consanguineous marriages within the Arab communities with low frequency of intermarriage between them, and the presence of genetic isolates and semi-isolates in some extended families and Bedouin tribes. Genetic services have been available in Kuwait for over a decade. During this time it has become clear that Arabs have a high frequency of genetic disorders, and in particular autosomal recessive traits. Their pattern is unique and some disorders are relatively common. Examples are Bardet-Biedl and Meckel syndromes, phenylketonuria, and familial Mediterranean fever. A relatively large number of new syndromes and variants have been delineated in Kuwait's population, many being the result of homozygosity for autosomal recessive genes that occurred because of inbreeding. Some of these syndromes have subsequently been found in other parts of the world, negating the concept of the private syndrome. This paper provides an overview of autosomal recessive disorders among the Arabs in Kuwait from a personal perspective and published studies, and highlights the need for genetic services in Arab countries with the goal of prevention and treatment of genetic disorders.