Novel mutations underlying argininosuccinic aciduria in Saudi Arabia

Identification of mutations in Malaysian patients with argininosuccinate lyase (ASL) deficiency

Argininosuccinate lyase (ASL) deficiency impairs the function of the urea cycle that detoxifies blood ammonia in the body. Mutation that occurs in the ASL gene is the cause of occurrence of ASL deficiency (ASLD). This deficiency causes hyperammonemia, hepatopathy and neurodevelopmental delay in patients. In this study, the clinical characteristics and molecular analysis of 10 ASLD patients were presented. 8 patients were associated with severe neonatal onset, while the other 2 were associated with late onset. Molecular analysis of ASL gene identified four new missense variants, which were c.778C>T, p.(Leu260Arg), c.1340G>C, p.(Ser447Thr), c.436C>G, p.(Arg146Gly) and c.595C>G, p.(Leu199Val) and four reported missense variants, which were c.638G>A, p.(Arg213Gln); c.556C>T, p.(Arg186Trp), c.578G>A, p.(Arg193Gln) and c.436C>G, p.(Arg146Trp). In silico servers predicted all new and reported variants as disease-causing. Structural examination exhibited that all pathogenic variants affected the stability of the tetrameric ASL structure by disturbing the bonding pattern with the neighboring residues.

Conclusion

This study revealed the genetic heterogeneity among Malaysian ASL patients. This study has also expanded the mutational spectrum of the ASL.

Urea cycle disorders in India: clinical course, biochemical and genetic investigations, and prenatal testing

Background

Urea cycle disorders (UCDs) are inherited metabolic disorders that present with hyperammonemia, and cause significant mortality and morbidity in infants and children. These disorders are not well reported in the Indian population, due to lack of a thorough study of the clinical and molecular profile.

Results

We present data from two major metabolic centres in India, including 123 cases of various UCDs. The majority of them (72/123, 58%) presented in the neonatal period (before 30 days of age) with 88% on or before day 7 of life (classical presentation), and had a high mortality (64/72, 88%). Citrullinemia type 1 was the most common UCD, observed in 61/123 patients. Ornithine transcarbamylase (OTC) deficiency was the next most common, seen in 24 cases. Argininosuccinic aciduria was diagnosed in 20 cases. Deficiencies of arginase, N-acetylglutamate synthase, carbamoyl phosphate synthetase, citrin, and lysinuric protein intolerance were also observed.

Molecular genetic analysis revealed two common ASS1 mutations: c.470G > A (p.Arg157His) and c.1168G > A (p.Gly390Arg) (36 of 55 tested patients). In addition, few recurrent point mutations in ASL gene, and a deletion of the whole OTC gene were also noted. A total of 24 novel mutations were observed in the various genes studied. We observed a poor clinical outcome with an overall all time mortality of 63% (70/110 cases with a known follow-up), and disability in 70% (28/40) among the survivors. Prenatal diagnosis was performed in 30 pregnancies in 25 families, including one pre-implantation genetic diagnosis.

Conclusions

We report the occurrence of UCDs in India and the spectrum that may be different from the rest of the world. Citrullinemia type 1 was the most common UCD observed in the cohort. Increasing awareness amongst clinicians will improve outcomes through early diagnosis and timely treatment. Genetic diagnosis in the proband will enable prenatal/pre-implantation diagnosis in subsequent pregnancies.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0908-1) contains supplementary material, which is available to authorized users.

A retrospective biochemical, molecular, and neurocognitive review of Saudi patients with argininosuccinic aciduria

A retrospective review was compiled of 54 patients with argininosuccinic aciduria who were either identified through the Saudi National Newborn Screening Program or diagnosed clinically from January 2000 to December 2015. The duration of follow-up is from 2 to 19 years. The majority of patients (65%) originated from the central province of Saudi Arabia. The mean patient age at review was 10 years (2-19 years), 92% received an early diagnosis (<28 days of age) and most were symptomatic at the time of the diagnosis (n = 34). Normal ammonia at diagnosis was reported in 30% of patients, who were detected under the newborn metabolic screen (n = 5/16). A very high rate of consanguinity was observed in our cohort (98%). Developmental delay was the most detectable long term neurocognitive consequence followed by seizure disorder; 90.7% (n = 49) and 62.9% (n = 34) respectively. As expected, the severe neonatal form was the major presentation. The most common variant identified in this cohort was the previously reported founder c.1060C > T; p.(Gln354*) nonsense mutation in the ASL gene. In addition, the frequency of hyperammonemia was higher in patients homozygous for c.1060C > T; p.(Gln354*) compared to the other mutations. Interestingly, frequent thrombocytosis with the mean level of 717 × 10⁹/L (range = 457-1169 × 10⁹/L) was observed in 96% of the patients with no clear explanation.