Metabolic Control and "Ideal" Outcomes in Liver Transplantation for Maple Syrup Urine Disease

An innocent bystander or a predisposing culprit? Kidney injury following pediatric liver transplantation

BACKGROUND

Survival after pediatric liver transplantation has increased dramatically over the years, revealing extra-hepatic complications including impaired kidney function. We conducted a large single-center retrospective study to evaluate kidney outcomes after pediatric liver transplantation.

METHODS

From electronic charts of 121 children who underwent liver transplantation during 2007-2020, we collected pre- and post-transplant data. We investigated the presence of post-transplant permanent kidney injury, including proteinuria, hypertension, and decreased estimated glomerular filtration rate (eGFR). We excluded children who died, underwent liver-kidney transplantation, or had less than 1 year of follow-up.

RESULTS

During a median follow-up of 5.1 (interquartile range 2.9-7.3) years, eGFR decreased, mostly in the first year post-transplant. In addition, 41% of the children presented with acute kidney injury. At their last follow-up, 35% showed permanent kidney injury (hypertension 13%, proteinuria 36%, and eGFR < 90 mL/min per 1.73 m2 7%). Kidney ultrasounds were abnormal for 44% of the children at the last visit, compared to 11% before transplant (p < 0.001). In multivariate analysis, abnormal kidney ultrasound before transplant (odds ratio = 4.53, 95% CI 1.1-18.7) and liver disease with potential risk of primary kidney involvement (odds ratio = 4.77, 95% CI 1.58-14.4) were predictors for hypertension or decreased eGFR at the last follow-up.

CONCLUSIONS

The high prevalence of kidney injury after pediatric liver transplantation and the pretransplant predictors for kidney injury highlight the importance of a thorough kidney pretransplant evaluation and follow-up.

Identifying Metabolic Diseases That Precipitate Neonatal Seizures

Although a rare cause of neonatal seizures, inborn errors of metabolism (IEMs) remain an essential component of a comprehensive differential diagnosis for poorly controlled neonatal epilepsy. Diagnosing neonatal-onset metabolic conditions proves a difficult task for clinicians; however, routine state newborn screening panels now include many IEMs. Three in particular-pyridoxine-dependent epilepsy, maple syrup urine disease, and Zellweger spectrum disorders-are highly associated with neonatal epilepsy and neurocognitive injury yet are often misdiagnosed. As research surrounding biomarkers for these conditions is emerging and gene sequencing technologies are advancing, clinicians are beginning to better establish early identification strategies for these diseases. In this literature review, the authors aim to present clinicians with an innovative clinical guide highlighting IEMs associated with neonatal-onset seizures, with the goal of promoting quality care and safety.

Oral enzyme therapy for maple syrup urine disease (MSUD) suppresses plasma leucine levels in intermediate MSUD mice and healthy nonhuman primates

Maple syrup urine disease (MSUD) is an inborn error of branched-chain amino acid metabolism affecting several thousand individuals worldwide. MSUD patients have elevated levels of plasma leucine and its metabolic product α-ketoisocaproate (KIC), which can lead to severe neurotoxicity, coma, and death. Patients must maintain a strict diet of protein restriction and medical formula, and periods of noncompliance or illness can lead to acute metabolic decompensation or cumulative neurological impairment. Given the lack of therapeutic options for MSUD patients, we sought to develop an oral enzyme therapy that can degrade leucine within the gastrointestinal tract prior to its systemic absorption and thus enable patients to maintain acceptable plasma leucine levels while broadening their access to natural protein. We identified a highly active leucine decarboxylase enzyme from Planctomycetaceae bacterium and used directed evolution to engineer the enzyme for stability to gastric and intestinal conditions. Following high-throughput screening of over 12 000 enzyme variants over 9 iterative rounds of evolution, we identified a lead variant, LDCv10, which retains activity following simulated gastric or intestinal conditions in vitro. In intermediate MSUD mice or healthy nonhuman primates given a whey protein meal, oral treatment with LDCv10 suppressed the spike in plasma leucine and KIC and reduced the leucine area under the curve in a dose-dependent manner. Reduction in plasma leucine correlated with decreased brain leucine levels following oral LDCv10 treatment. Collectively, these data support further development of LDCv10 as a potential new therapy for MSUD patients.

Treatment of maple syrup urine disease: Benefits, risks, and challenges of liver transplantation

Maple syrup urine disease (MSUD) is caused by a deficiency in the activity of the branched-chain α-ketoacid dehydrogenase (BCKD) complex, promoting the accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine, and valine, as well as their respective α-keto acids. MSUD is an autosomal recessive hereditary metabolic disorder characterized by ketoacidosis, ataxia, coma, and mental and psychomotor retardation. The mechanisms involved in the brain damage caused by MSUD are not fully understood. Early diagnosis and treatment, as well as proper control of metabolic decompensation crises, are crucial for patients' survival and for a better prognosis. The recommended treatment consists of a high-calorie diet with restricted protein intake and specific formulas containing essential amino acids, except those accumulated in MSUD. This treatment will be maintained throughout life, being adjusted according to the patients' nutritional needs and BCAA concentration. Because dietary treatment may not be sufficient to prevent neurological damage in MSUD patients, other therapeutic strategies have been studied, including liver transplantation. With transplantation, it is possible to obtain an increase of about 10% of the normal BCKD in the body, an amount sufficient to maintain amino acid homeostasis and reduce metabolic decompensation crises. However, the experience related to this practice is very limited when considering the shortage of liver for transplantation and the risks related to the surgical procedure and immunosuppression. Thus, the purpose of this review is to survey the benefits, risks, and challenges of liver transplantation in the treatment of MSUD.

Newborn screening of maple syrup urine disease and the effect of early diagnosis

BACKGROUND

Maple syrup urine disease (MSUD) is a rare disease for which newborn screening (NBS) is feasible but not universally applied in China. We shared our experiences with MSUD NBS.

METHODS

Tandem mass spectrometry-based NBS for MSUD was implemented in January 2003, and diagnostic methods included urine organic acid analysis via gas chromatography-mass spectrometry and genetic analysis.

RESULTS

Six MSUD patients were identified from 1.3 million newborns, yielding an incidence of 1:219,472, in Shanghai, China. The areas under the curve (AUCs) of total leucine (Xle), Xle/phenylalanine ratio, and Xle/alanine ratio were all 1.000. Some amino acid and acylcarnitine concentrations were markedly low in MSUD patients. 47 MSUD patients identified here and in other centers were investigated, which included 14 patients identified by NBS and 33 patients diagnosed clinically. Forty-four patients were subclassified into classic (n = 29), intermediate (n = 11) and intermittent (n = 4) subtypes. Due to earlier diagnosis and treatment, screened classic patients showed a higher survival rate (62.5%, 5/8) than clinically diagnosed classic patients (5.2%, 1/19). Overall, 56.8% (25/44) of MSUD patients and 77.8% (21/27) of classic patients carried variants in the BCKDHB gene. Among 61 identified genetic variants, 16 novel variants were identified.

CONCLUSION

MSUD NBS in Shanghai, China, enabled earlier detection and increased survivorship in the screened population.

Neonatal maple syrup urine disease case report and literature review

RATIONALE

The main clinical symptoms of maple syrup urine disease (MSUD) are dehydration, acidosis, nervous system symptoms and intellectual disability. The brain imaging findings were mainly caused by cytotoxic edema. The lesions usually occur at the site consistent with the myelination process of normal neonates. The distribution is mostly symmetric, and the diffusion is obviously limited.

PATIENT CONCERNS

Herein, we report a rare case of an 8-day-old female patient who presented with abnormal symptoms, such as difficulty eating, convulsions, slow reaction, difficulty in correcting hypoglycemia and severe metabolic disorders. Brain magnetic resonance imaging (MRI) revealed abnormal signal intensity mainly involving the brainstem, cervical spinal cord, bilateral cerebellar hemispheres, basal ganglia, thalamus, precentral gyrus, and postcentral gyrus with characteristic hyperintensity on diffusion-weighted imaging (DWI) sequence. MSUD is rarely reported, while cervical spinal cord involvement is extremely rare.

DIAGNOSES

Blood tandem mass spectrometry, urine organic acid detection, and genetic disease overall genetic tests were performed to further confirm the diagnosis of MSUD.

INTERVENTIONS

Under general anesthesia, she underwent open surgical procedures for liver transplantation.

OUTCOMES

The child was in a stable condition after liver transplantation, and the diet was not restricted.

LESSONS

MSUD in neonates is rare. Our case report and literature review was aim to describe the clinic and imaging characteristics of it, and highlight physicians must be aware of this entity in newborns so as to reduce misdiagnosis due to unfamiliarity.