Fatal metabolic stroke in a child with propionic acidemia 11 years post liver transplant

Prevalence of propionic acidemia in China

Propionic acidemia (PA) is a rare autosomal recessive congenital disease caused by mutations in the PCCA or PCCB genes. Elevated propionylcarnitine, 2-methylcitric acid (2MCA), propionylglycine, glycine and 3-hydroxypropionate can be used to diagnose PA. Early-onset PA can lead to acute deterioration, metabolic acidosis, and hyperammonemia shortly after birth, which can result in high mortality and disability. Late-onset cases of PA have a more heterogeneous clinical spectra, including growth retardation, intellectual disability, seizures, basal ganglia lesions, pancreatitis, cardiomyopathy, arrhythmias, adaptive immune defects, rhabdomyolysis, optic atrophy, hearing loss, premature ovarian failure, and chronic kidney disease. Timely and accurate diagnosis and appropriate treatment are crucial to saving patients' lives and improving their prognosis. Recently, the number of reported PA cases in China has increased due to advanced diagnostic techniques and increased research attention. However, an overview of PA prevalence in China is lacking. Therefore, this review provides an overview of recent advances in the pathogenesis, diagnostic strategies, and treatment of PA, including epidemiological data on PA in China. The most frequent variants among Chinese PA patients are c.2002G > A in PCCA and c.1301C > T in PCCB, which are often associated with severe clinical symptoms. At present, liver transplantation from a living (heterozygous parental) donor is a better option for treating PA in China, especially for those exhibiting a severe metabolic phenotype and/or end-organ dysfunction. However, a comprehensive risk-benefit analysis should be conducted as an integral part of the decision-making process. This review will provide valuable information for the medical care of Chinese patients with PA.

Pathophysiological mechanisms of complications associated with propionic acidemia

Propionic acidemia (PA) is a genetic metabolic disorder caused by mutations in the mitochondrial enzyme, propionyl-CoA carboxylase (PCC), which is responsible for converting propionyl-CoA to methylmalonyl-CoA for further metabolism in the tricarboxylic acid cycle. When this process is disrupted, propionyl-CoA and its metabolites accumulate, leading to a variety of complications including life-threatening cardiac diseases and other metabolic strokes. While the clinical symptoms and diagnosis of PA are well established, the underlying pathophysiological mechanisms of PA-induced diseases are not fully understood. As a result, there are currently few effective therapies for PA beyond dietary restriction. This review focuses on the pathophysiological mechanisms of the various complications associated with PA, drawing on extensive research and clinical reports. Most research suggests that propionyl-CoA and its metabolites can impair mitochondrial energy metabolism and cause cellular damage by inducing oxidative stress. However, direct evidence from in vivo studies is still lacking. Additionally, elevated levels of ammonia can be toxic, although not all PA patients develop hyperammonemia. The discovery of pathophysiological mechanisms underlying various complications associated with PA can aid in the development of more effective therapeutic treatments. The consequences of elevated odd-chain fatty acids in lipid metabolism and potential gene expression changes mediated by histone propionylation also warrant further investigation.

Therapeutic potential of living donor liver transplantation from heterozygous carrier donors in children with propionic acidemia

Background

Current world experience regarding living donor liver transplantation (LDLT) in the treatment of propionic acidemia (PA) is limited, especially in terms of using obligate heterozygous carriers as donors. This study aimed to evaluate the clinical outcomes of LDLT in children with PA.

Methods

From November 2017 to January 2020, 7 of the 192 children who underwent LDLT at our institution had been diagnosed with PA (median age, 2.1 years; range, 1.1–5.8 years). The primary indication for transplantation was frequent metabolic decompensations in 6 patients and preventative treatment in 1 patient. Of the seven parental living donors, six were genetically proven obligate heterozygous carriers.

Results

During a median follow-up of 23.9 months (range, 13.9–40.2 months), all patients were alive with 100% allograft survival, and no severe transplant-related complications occurred. In the case of liberalized protein intake, they did not suffer metabolic decompensation or disease-related complications and made progress in neurodevelopmental delay and body growth, as well as blood and urinary metabolite levels. In one patient with pre-existing mild dilated cardiomyopathy, her echocardiogram results completely normalized 13.8 months post-transplant. All living donors recovered well after surgery, with no metabolic decompensations or procedure-related complications. Western blotting revealed that the hepatic expressions of PCCA and PCCB in one of the heterozygous donors were comparable to those of the normal healthy control at the protein level.

Conclusions

LDLT using partial liver grafts from asymptomatic obligate heterozygous carrier donors is a viable therapeutic option for selected PA patients, with no negative impact on donors’ and recipients' clinical courses.