Propionic acidemia (PA) is an organic aciduria caused by inherited deficiency of propionyl-CoA carboxylase. Left ventricular dysfunction and QT prolongation may lead to life-threatening ...complications. Systematic analyses of cardiac phenotypes, in particular effects of specific cardiac therapies, are scarce.
In this longitudinal observational monocentric study (data from 1989 to 2017) all PA patients treated at our center were included. Echocardiographic parameters (left ventricular end-diastolic diameter: LVEDD, left ventricular shortening fraction, mitral valve Doppler inflow pattern) and 12‑lead electrocardiogram recordings (corrected QT interval: QTc) were analyzed. Symptomatic patients were dichotomized to the group “early-onset” (symptoms within 28 days of life) and “late-onset” (symptoms after 28 days). Associations between cardiac function, LVEDD, QTc and clinical parameters (age at onset, beta-blocker or Angiotensin-converting enzyme inhibitor = ACE-I therapy) were analyzed.
18 patients with PA were enrolled, 17 of them were symptomatic and one asymptomatic, with a median age at diagnosis of 6 days. 14/17 (82%) had early onset disease manifestation. Systolic left ventricular dysfunction (i.e. hypokinetic phenotype of cardiomyopathy) was diagnosed in 7/18 (39%) patients at a median age of 14.4 years, all had early onset. Two patients had a dilated left ventricle and systolic left ventricular dysfunction (i.e. dilated hypokinetic phenotype – dilated cardiomyopathy). Diastolic left ventricular dysfunction was found in 11/18 (61%) individuals, typically preceding systolic left ventricular dysfunction. ACE-I therapy did not improve systolic left ventricular function. Mean QTc was 445 ms (+/− 18.11 ms). Longer QTc was associated with larger LVEDD.
Systolic left ventricular dysfunction was found in 39% of patients, reflecting high disease severity. Two thirds of all individuals showed signs of diastolic left ventricular dysfunction usually preceding systolic left ventricular dysfunction; it therefore may be considered as an indicator for early cardiac disease manifestation, possibly allowing earlier treatment modification. Unresponsiveness to routine cardiac therapy highlights the need to evaluate further strategies, such as liver transplantation.
Methylmalonic acidurias (MMAurias) are a group of inherited disorders in the catabolism of branched-chain amino acids, odd-chain fatty acids and cholesterol caused by complete or partial deficiency ...of methylmalonyl-CoA mutase (mut(0) and mut(-) subtype respectively) and by defects in the metabolism of its cofactor 5'-deoxyadenosylcobalamin (cblA, cblB or cblD variant 2 type). A long-term complication found in patients with mut(0) and cblB variant is chronic tubulointerstitial nephritis. The underlying pathomechanism has remained unknown. We established an in vitro model of tubular epithelial cells from patient urine (hTEC; 9 controls, 5 mut(0), 1 cblB). In all human tubular epithelial cell (hTEC) lines we found specific tubular markers (AQP1, UMOD, AQP2). Patient cells showed disturbance of energy metabolism in glycolysis, mitochondrial respiratory chain and Krebs cycle in concert with increased reactive oxygen species (ROS) formation. Electron micrographs indicated increased autophagosome production and endoplasmic reticulum stress, which was supported by positive acridine orange staining and elevated levels of LC3 II, P62 and pIRE1. Screening mTOR signaling revealed a release of inhibition of autophagy. Patient hTEC produced and secreted elevated amounts of the pro-inflammatory cytokine IL8, which was highly correlated with the acridine orange staining. Summarizing, hTEC of MMAuria patients are characterized by disturbed energy metabolism and ROS production that lead to increased autophagy and IL8 secretion.
Acute encephalopathic crisis in glutaryl‐CoA dehydrogenase deficiency results in an unfavourable disease course and poor outcome, dominated by dystonia, feeding problems, seizures and secondary ...complications, and quite often leading to early death. The prerequisite for the prevention of irreversible brain damage in this disease is the detection of affected patients and initiation of treatment before the manifestation of such crisis. Apart from macrocephaly there are no signs or symptoms characteristic for this disease in presymptomatic children and, thus, they are usually missed. In some countries, implementation of extended neonatal screening programmes using electrospray ionization tandem mass spectrometry (ESI‐MS/MS) allows detection of affected newborns and start of therapy before onset of neurological complications. This article summarizes recent strategies, pitfalls and shortcomings of a mass screening for glutaryl‐CoA dehydrogenase deficiency using ESI‐MS/MS. Furthermore, an alternative strategy, namely DNA‐based neonatal screening for the Oji‐Cree variant of this disease, is demonstrated. An optimization of diagnostic as well as therapeutic procedures must be achieved before GCDH deficiency unequivocally fullfils the criteria of a reliable and successful newborn screening programme.
Summary
Glutaryl‐CoA dehydrogenase (GCDH) deficiency is an autosomal recessive disease with an estimated overall prevalence of 1 in 100 000 newborns. Biochemically, the disease is characterized by ...accumulation of glutaric acid, 3‐hydroxyglutaric acid, glutaconic acid, and glutarylcarnitine, which can be detected by gas chromatography–mass spectrometry of organic acids or tandem mass spectrometry of acylcarnitines. Clinically, the disease course is usually determined by acute encephalopathic crises precipitated by infectious diseases, immunizations, and surgery during infancy or childhood. The characteristic neurological sequel is acute striatal injury and, subsequently, dystonia. During the last three decades attempts have been made to establish and optimize therapy for GCDH deficiency. Maintenance treatment consisting of a diet combined with oral supplementation of L‐carnitine, and an intensified emergency treatment during acute episodes of intercurrent illness have been applied to the majority of patients. This treatment strategy has significantly reduced the frequency of acute encephalopathic crises in early‐diagnosed patients. Therefore, GCDH deficiency is now considered to be a treatable condition. However, significant differences exist in the diagnostic procedure and management of affected patients so that there is a wide variation of the outcome, in particular of pre‐symptomatically diagnosed patients. At this time of rapid expansion of neonatal screening for GCDH deficiency, the major aim of this guideline is to re‐assess the common practice and to formulate recommendations for diagnosis and management of GCDH deficiency based on the best available evidence.
Chronic renal failure is a well-known long-term complication of methylmalonic aciduria (MMA-uria), occurring even under apparently optimal metabolic management. The onset of renal dysfunction seems ...to be dependent on the type of defect and vitamin B12-responsiveness. We report on a patient with a vitamin B12-responsive cobalamin A type (cblA) MMA-uria caused by a homozygous stop mutation (p.R145X) in the cobalamin A gene (MMAA). She was diagnosed with chronic kidney disease (CKD) stage III at the age of 12years. Following re-evaluation, the patient received vitamin B12 (hydroxocobalamin) treatment, resulting in a significant decrease in the concentration of methylmalonic acid (MMA) in urine and plasma. Until age 29years glomerular filtration rate remained stable probably due to hydroxocobalamin treatment slowing down progression to end-stage renal failure. Kidney biopsies showed non-specific manifestations of chronic interstitial inflammation. The patient received a renal transplant at age 35years. Under continuous treatment with hydroxocobalamin there is no evidence of kidney damage due to MMA-uria until the last follow-up 6years after transplantation.
This case report illustrates (i) a long-term follow-up of a patient with MMA-uria due to cblA deficiency, (ii) the involvement of the kidney as a target organ and (iii) the importance of early and adequate vitamin B12 substitution in responsive patients. Further investigation will be necessary to prove the protective effect of hydroxocobalamin in the kidney in vitamin B12-responsive patients.
•A long-term follow-up of a patient with MMA-uria due to cblA deficiency•A detailed description of the involvement of the kidney as a target organ•The importance of early and adequate vitamin B12 substitution in responsive patients•Isolated kidney transplantation as a valid option for treatment in such patients
Methylmalonic acid was previously considered as major neurotoxin in methylmalonic acidurias. In contrast, recent studies support the notion that other metabolites deriving from propionyl-coenzyme A, ...inducing synergistic inhibition of mitochondrial energy metabolism, are more important than methylmalonic acid to understand the neuropathogenesis of this disease. However, it is not yet known whether methylmalonic acid is involved in the induction of other organ manifestations in this disease, such as chronic renal failure.
Adenosine kinase deficiency (ADK deficiency) is a recently described disorder of methionine and adenosine metabolism resulting in a neurological phenotype with developmental delay, muscular ...hypotonia, and epilepsy as well as variable systemic manifestations. The underlying neuropathology is poorly understood. We have investigated MRI and (1)H-MRS changes in ADK deficiency in order to better understand the in vivo neuropathologic changes of ADK deficiency.
Systematic evaluation of 21 MRIs from eight patients (age range 9 days-14.6 years, mean 3.9 years, median 2.7 years) including diffusion-weighted imaging in six and (1)H-MRS in five patients.
Brain maturation was delayed in the neonatal period and in infancy (6/6), but ultimately complete. White matter changes occurring in five of eight patients were discrete, periventricular, and unspecific (4/5), or diffuse with sparing of optic radiation, corona radiata, and pyramidal tracts (1/5). Choline was low in white matter spectra (3/3), while there was no indication of low creatine in white matter or basal ganglia (5/5), and diffusion was variably decreased or increased. Central tegmental tract hyperintensity was a common finding (6/8), as was supratentorial atrophy (6/8).
MRI changes in ADK deficiency consist of delayed but ultimately completed brain maturation with later onset of mostly unspecific white matter changes and potentially transient central tegmental tract hyperintensity. Immaturity on neonatal MRI is consistent with prenatal onset of disease and reduced choline with lower membrane turnover resulting in delayed myelination and deficient myelin maintenance.
Summary
In the last decades the survival of patients with methylmalonic aciduria has been improved. However, the overall outcome of affected patients remains disappointing. The disease course is ...often complicated by acute life-threatening metabolic crises, which can result in multiple organ failure or even death, resembling primary defects of mitochondrial energy metabolism. Biochemical abnormalities during metabolic derangement, such as metabolic acidosis, ketonaemia/ketonuria, lactic acidosis, hypoglycaemia and hyperammonaemia, suggest mitochondrial dysfunction. In addition, long-term complications such as chronic renal failure and neurological disease are frequently found. Neuropathophysiological studies have focused on various effects caused by accumulation of putatively toxic organic acids, the so-called ‘toxic metabolite’ hypothesis. In previous studies, methylmalonate (MMA) has been considered as the major neurotoxin in methylmalonic aciduria, whereas more recent studies have highlighted a synergistic inhibition of mitochondrial energy metabolism (pyruvate dehydrogenase complex, tricarboxylic acid cycle, respiratory chain, mitochondrial salvage pathway of deoxyribonucleoside triphosphate (dNTP)) induced by propionyl-CoA, 2-methylcitrate and MMA as the key pathomechanism of inherited disorders of propionate metabolism. Intracerebral accumulation of toxic metabolites (‘trapping’ hypothesis’) is considered a biochemical risk factor for neurodegeneration. Secondary effects of mitochondrial dysfunction, such as oxidative stress and impaired mtDNA homeostasis, contribute to pathogenesis of these disorders. The underlying pathomechanisms of chronic renal insufficiency in methylmalonic acidurias are not yet understood. We hypothesize that renal and cerebral pathomechanisms share some similarities, such as an involvement of dicarboxylic acid transport. This review aims to give a comprehensive overview on recent pathomechanistic concepts for methylmalonic acidurias.
Pathogenic biallelic variants in PCK1 coding for the cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) cause PEPCK-C deficiency, a rare disorder of gluconeogenesis presenting with hypoglycemia, ...lactic acidosis, and hepatopathy. To date, there has been no systematic analysis of its phenotypic, biochemical, and genetic spectrum.
All currently published individuals and a novel patient with genetically confirmed PEPCK-C deficiency were included. Clinical, biochemical, and genetic findings were analyzed. Protein and in-silico prediction score modeling was applied to analyze potential variant effects.
Thirty-two individuals from 25 families were found, including one previously unreported patient. The typical biochemical pattern was hypoglycemia triggered by catabolic situations, elevated urinary concentrations of tricarboxylic acid cycle metabolites, mildly elevated alanine and aspartate aminotransferase and elevated lactate concentrations in serum. Plasma glutamine concentrations were elevated in some patients and may be a suitable marker for newborn screening. With adequate treatment, biochemical abnormalities usually normalized following a hypoglycemic episode. Symptom onset usually occurred in infancy with a broad range from neonatal age to adulthood. Regardless of the genotype, different phenotypes with a broad clinical spectrum were found. To date, eight genotypes with nine different PCK1 variants were identified, of which alleles with the recurrent variant c.925G > A; p.(Gly309Arg) are predominant and appear to be endemic in the Finnish population. Protein modeling suggests altered manganese- and substrate-binding as superordinate pathomechanisms.
Environmental factors appear to be the main determinant for the phenotype in patients with biallelic variants in PCK1. Based on the biochemical pattern, PEPCK-C deficiency is a recognizable cause of childhood hypoglycemia. It is a treatable disease and early diagnosis is important to prevent metabolic derailment and morbidity. Newborn screening can identify at least a sub-cohort of affected individuals through elevated glutamine concentrations in dry blood.
Summary
With the introduction of tandem mass spectrometry, newborn screening for disorders of propionate metabolism became widely available. However, there is controversy whether population screening ...for these disorders should be performed. The most widely used primary metabolite C
3
itself has a poor specificity or lacks 100% sensitivity for milder forms and/or defects of cobalamin metabolism. Strategies to improve specificity have included the calculation of metabolite ratios (e.g. C
3
/C
2
) or second-tier strategies with analysis of methylmalonic acid or 2-methylcitric acid from the primary screening specimen. We report the results of a new statistical approach to identify parameter combinations that allow for 100% sensitivity as well as increased specificity. The promising results of this alternative approach will have to be substantiated on larger data sets.
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