Retrospective evaluations revealed pre-symptomatic citrulline concentrations measured by newborn screening were significantly low in late-onset ornithine transcarbamylase deficiency patients

A preliminary retrospective evaluation of screening and diagnosis of ornithine transcarbamylase deficiency in high-risk patients at a referral center in Vietnam

Introduction

To date, newborn screening (NBS) for proximal urea cycle disorders, including Ornithine transcarbamylase deficiency (OTCD), was not recommended due to the lack of appropriate tests and insufficient evidence of the benefits. This study aimed to investigate the potential of tandem mass spectrometry (MS/MS) for OTCD screening and its value in guiding further investigation to obtain a final diagnosis in high-risk patients.

Methods

The study included patients with OTCD referred to the National Children's Hospital between April 2020 and November 2023. A retrospective evaluation of amino acid concentrations measured by MS/MS and their ratios in patients with early-onset and late-onset OTCD was conducted.

Results

While all ten early-onset cases had glutamine concentrations above the upper limit, only five of them had citrulline concentrations below the lower limit of the reference interval. Only two late-onset cases had elevated glutamine levels, while all had citrulline within reference intervals. The Cit/Phe ratio was decreased, and the Gln/Cit and Met/Cit ratios were increased in all early-onset OTCD cases, while they were abnormal in only one late-onset case.

Conclusions

The preliminary results suggest that hyperglutaminemia, in combination with low or normal citrulline concentrations and specific ratios (Gln/Cit, Met/Cit, and Cit/Phe), can serve as reliable markers for screening early-onset OTCD in high-risk patients. However, these markers proved less sensitive for detecting the late-onset form, even in symptomatic patients.

Synergistic effects of pH shift and heat treatment on solubility, physicochemical and structural properties, and lysinoalanine formation in silkworm pupa protein isolates

The application of silkworm pupa protein isolates (SPPI) in food industry was limited because SPPI's solubility is poor and it contains a potential harmful component of lysinoalanine (LAL) which formed during protein extraction. In this study, combined treatments of pH shift and heating were performed to improve the solubility of SPPI and to reduce the content of LAL. The experimental results showed that the promoting effect on SPPI's solubility by alkaline pH shift + heat treatment was greater than that by acidic pH shift + heat. And an 8.62 times increase of solubility was observed after pH 12.5 + 80 ℃ treatment compared to the control SPPI sample which was extracted at pH 9.0 without pH shift treatment. Very strong positive correlation was found between alkali dosage and SPPI solubility (Pearson's correlation coefficient r = 0.938). SPPI with pH 12.5 shift treatment showed the highest thermal stability. Alkaline pH shift combined with heat treatment altered the micromorphology of SPPI and destroyed the disulfide bonds between macromolecular subunits (72 and 95 kDa), resulting in reduced particle size and increased zeta potential and free sulfhydryl content of the isolates. The fluorescence spectra analysis showed red shifts phenomena with pH increasing and fluorescence intensity increase with temperature increasing, implying the alterations in the tertiary structure of protein. Compared to the control SPPI sample, the amount of LAL reduced by 47.40 %, 50.36 % and 52.39 % using pH 12.5 + 70 ℃, pH 12.5 + 80 ℃ and pH 12.5 + 90 ℃ treatment, respectively. These findings provide fundamental information for the development and application of SPPI in food industry.

Pathogenic variants of ornithine transcarbamylase deficiency: Nation-wide study in Japan and literature review

Ornithine transcarbamylase deficiency (OTCD) is an X-linked disorder. Several male patients with OTCD suffer from severe hyperammonemic crisis in the neonatal period, whereas others develop late-onset manifestations, including hyperammonemic coma. Females with heterozygous pathogenic variants in the OTC gene may develop a variety of clinical manifestations, ranging from asymptomatic conditions to severe hyperammonemic attacks, owing to skewed lyonization. We reported the variants of CPS1, ASS, ASL and OTC detected in the patients with urea cycle disorders through a nation-wide survey in Japan. In this study, we updated the variant data of OTC in Japanese patients and acquired information regarding genetic variants of OTC from patients with OTCD through an extensive literature review. The 523 variants included 386 substitution (330 missense, 53 nonsense, and 3 silent), eight deletion, two duplication, one deletion-insertion, 55 frame shift, two extension, and 69 no category (1 regulatory and 68 splice site error) mutations. We observed a genotype-phenotype relation between the onset time (neonatal onset or late onset), the severity, and genetic mutation in male OTCD patients because the level of deactivation of OTC significantly depends on the pathogenic OTC variants. In conclusion, genetic information about OTC may help to predict long-term outcomes and determine specific treatment strategies, such as liver transplantation, in patients with OTCD.