Sara Boenzi

Methylmalonic and propionic aciduria

Methylmalonic and propionic aciduria (PA) are the most frequent forms of branched‐chain organic acidurias. These autosomal recessive disorders result from deficient activity of methylmalonyl‐CoA mutase and propionyl‐CoA carboxylase, respectively. Clinically, acute or chronic neurologic signs are caused by the accumulation of toxic compounds proximal to the metabolic block. Phenotype varies from severe neonatal‐onset forms with high mortality and poor outcome to milder forms with a later onset. In both cases the clinical course is dominated by the risk of relapses of life‐threatening episodes of metabolic decompensation and of severe organ failure. Despite improvement of treatment, the overall outcome remains disappointing with no major differences between the two diseases. The diagnosis is based on the presence of characteristic compounds in body fluids as detected by organic acid analysis in urine and acylcarnitine profile in blood. Therapy is based on low‐protein high‐energy diet, carnitine supplementation, and metronidazole. Some patients with methylmalonic aciduria (MMA) respond to pharmacological doses of vitamin B12. Given the poor long‐term prognosis, liver transplantation has been recently attempted as an alternative therapy to conventional medical treatment to cure the underlying metabolic defect. Nevertheless, the overall experience to date does not clearly demonstrate its effectiveness in preventing further deterioration or improving survival and quality of life. The recent implementation of neonatal screening by electrospray tandem mass spectrometry has decreased early mortality and improved the short‐term outcome, without changing the detection rate of both diseases in the screening population compared to clinically detected cases. However, the limited number of patients and the short duration of their follow‐up do not yet permit drawing final conclusions on its effect on the long‐term outcome of methylmalonic and propionic acidemia.

Spectrum of MMACHC mutations in Italian and Portuguese patients with combined methylmalonic aciduria and homocystinuria, cblC type.

Methylmalonic aciduria (MMA) and homocystinuria, cblC type (MIM 277400) is the most frequent inborn error of vitamin B(12). The recent identification of the disease gene, MMACHC, has permitted preliminary genotype-phenotype correlations. We studied 24 Italian and 17 Portuguese patients with cblC defect to illustrate the spectrum of mutations in a southern European population and discuss the impact that mutation identification has on routine diagnostic procedures. Since the metabolic defect raises the serum levels of homocysteine, we also tested if variants in MTHFR-playing a key role in homocysteine remethylation pathway-could act as genetic modifier in cblC defect. We found that the c.271dupA (accounting for 55% of the MMACH alleles in our cohort) followed by c.394C>T (16%) and c.331C>T (9%) were the most frequent mutations. In our study we also identified a novel mutation (c.544T>C). On the other hand, the MTHFR genotype did not appear to influence age at onset, the clinical phenotype and outcome of patients with cblC defect. This study shows that mutation screening for the most common MMACH mutations occurring in early-onset forms (c.271dupA and c.331C>T) seems to have a high diagnostic yield in a southern European population with cblC defect. Although the identification of the gene defect per se does not predict completely time and severity of disease appearance, our data corroborate the importance of a molecular testing to offer accurate prenatal diagnosis to couples at high risk of having affected children.

Characteristic Acylcarnitine Profiles in Inherited Defects of Peroxisome Biogenesis: A Novel Tool for Screening Diagnosis Using Tandem Mass Spectrometry

Patients with inherited defects of peroxisomal metabolism, a class of diseases with marked clinical and genetic heterogeneity, show a characteristic phenotype in most cases with severe neurologic impairment, craniofacial abnormalities, and hepatic and kidney dysfunction. For the differential diagnosis of clinically suspected cases, a complex biochemical and genetic approach is required. Analysis of plasma very-long-chain fatty acids is a reliable screening method to detect most but not all peroxisomal disorders. To study the potential presence of abnormal acylcarnitine species in plasma and blood, we screened by tandem mass spectrometry a series of patients affected by a peroxisome biogenesis disorder (PBD) and compared the results with those obtained in patients with isolated peroxisomal defects (e.g. D-bifunctional protein deficiency, X-linked adrenoleukodystrophy) and mitochondrial long-chain fatty acid oxidation defects. The most relevant finding observed in plasma of patients with PBD was a significant increase of long-chain dicarboxylic C16- and C18-carnitine, i.e. hexadecanedioyl- and octadecanedioyl-carnitine, with high dicarboxylycarnitine/monocarboxylylcarnitine ratio. Elevation of very long-chain acylcarnitines C24- and C26-, i.e. lignoceroyl- and cerotoyl-carnitine, was detected in some PBDs and in D-bifunctional protein deficiency. Similar abnormalities were also found in neonatal screening blood spots. Detection of these compounds alone, in the absence of other shorter-chain acylcarnitines, is highly specific and characteristic of PBD, as confirmed by the differing profiles observed in patients with adrenoleukodystrophy and mitochondrial long-chain fatty acid oxidation defects. Our study adds a novel method to the diagnosis of PBD, which may also be of benefit for future neonatal mass screening programs based on acylcarnitine profiling.

A new simple and rapid LC–ESI-MS/MS method for quantification of plasma oxysterols as dimethylaminobutyrate esters. Its successful use for the diagnosis of Niemann–Pick type C disease

Two oxysterols, cholestan-3β,5α,6β-triol (C-triol) and 7-ketocholesterol (7-KC), have been recently proposed as diagnostic markers of Niemann-Pick type C (NP-C) disease, representing a potential alternative diagnostic tool to the more invasive and time consuming filipin test in cultured fibroblasts. Usually, the oxysterols are detected and quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) method using atmospheric pressure chemical ionization (APCI) or electro-spray-ionization (ESI) sources, after a variety of derivatization procedures to enhance sensitivity. We developed a sensitive LC-MS/MS method to quantify the oxysterols in plasma as dimethylaminobutyrate ester, suitable for ESI analysis. This method, with an easy liquid-phase extraction and a short derivatization procedure, has been validated to demonstrate specificity, linearity, recovery, lowest limit of quantification, accuracy and precision. The assay was linear over a concentration range of 0.5-200ng/mL for C-triol and 1.0-200ng/mL for 7-KC. Intra-day and inter-day coefficients of variation (CV%) were <15% for both metabolites. Receiver operating characteristic analysis estimates that the area under curve was 0.998 for C-triol, and 0.972 for 7-KC, implying a significant discriminatory power for the method in this patient population of both oxysterols. In summary, our method provides a simple, rapid and non-invasive diagnostic tool for the biochemical diagnosis of NP-C disease.

Understanding pyrroline-5-carboxylate synthetase deficiency: clinical, molecular, functional, and expression studies, structure-based analysis, and novel therapy with arginine

AbstractΔ1-Pyrroline-5-carboxylate synthetase (P5CS) catalyzes the first two steps of ornithine/proline biosynthesis. P5CS deficiency has been reported in three families, with patients presenting with cutis/joint laxity, cataracts, and neurodevelopmental delay. Only one family exhibited metabolic changes consistent with P5CS deficiency (low proline/ornithine/citrulline/arginine; fasting hyperammonemia). Here we report a new P5CS-deficient patient presenting the complete clinical/metabolic phenotype and carrying p.G93R and p.T299I substitutions in the γ-glutamyl kinase (γGK) component of P5CS. The effects of these substitutions are (1) tested in mutagenesis/functional studies with E.coli γGK, (2) rationalized by structural modelling, and (3) reflected in decreased P5CS protein in patient fibroblasts (shown by immunofluorescence). Using optical/electron microscopy on skin biopsy, we show collagen/elastin fiber alterations that may contribute to connective tissue laxity and are compatible with our angio-MRI finding of kinky brain vessels in the patient. MR spectroscopy revealed decreased brain creatine, which normalized after sustained arginine supplementation, with improvement of neurodevelopmental and metabolic parameters, suggesting a pathogenic role of brain creatine decrease and the value of arginine therapy. Morphological and functional studies of fibroblast mitochondria show that P5CS deficiency is not associated with the mitochondrial alterations observed in Δ1-pyrroline-5-carboxylate reductase deficiency (another proline biosynthesis defect presenting cutis laxa and neurological alterations).

Evaluation of plasma cholestane-3β,5α,6β-triol and 7-ketocholesterol in inherited disorders related to cholesterol metabolism

Oxysterols are intermediates of cholesterol metabolism and are generated from cholesterol via either enzymatic or nonenzymatic pathways under oxidative stress conditions. Cholestan-3β,5α,6β-triol (C-triol) and 7-ketocholesterol (7-KC) have been proposed as new biomarkers for the diagnosis of Niemann-Pick type C (NP-C) disease, representing an alternative tool to the invasive and time-consuming method of fibroblast filipin test. To test the efficacy of plasma oxysterol determination for the diagnosis of NP-C, we systematically screened oxysterol levels in patients affected by different inherited disorders related with cholesterol metabolism, which included Niemann-Pick type B (NP-B) disease, lysosomal acid lipase (LAL) deficiency, Smith-Lemli-Opitz syndrome (SLOS), congenital familial hypercholesterolemia (FH), and sitosterolemia (SITO). As expected, NP-C patients showed significant increase of both C-triol and 7-KC. Strong increase of both oxysterols was observed in NP-B and less pronounced in LAL deficiency. In SLOS, only 7-KC was markedly increased, whereas in both FH and in SITO, oxysterol concentrations were normal. Interestingly, in NP-C alone, we observed that plasma oxysterols correlate negatively with patient’s age and positively with serum total bilirubin, suggesting the potential relationship between oxysterol levels and hepatic disease status. Our results indicate that oxysterols are reliable and sensitive biomarkers of NP-C.

Glutathione metabolism in cobalamin deficiency type C (cblC).

BackgroundMethylmalonic aciduria with homocystinuria, cblC defect, is the most frequent disorder of vitamin B12 metabolism. CblC patients are commonly treated with a multidrug therapy to reduce metabolite accumulation and to increase deficient substrates. However the long-term outcome is often unsatisfactory especially in patients with early onset, with frequent progression of neurological and ocular impairment. Recent studies, have shown perturbation of cellular redox status in cblC. To evaluate the potential contribution of oxidative stress into the patophysiology of cblC defect, we have analyzed the in vivo glutathione metabolism in a large series of cblC deficient individuals.MethodsLevels of different forms of glutathione were measured in lymphocytes obtained from 18 cblC patients and compared with age-matched controls. Furthermore, we also analyzed plasma cysteine and total homocysteine.ResultsWe found an imbalance of glutathione metabolism in cblC patients with a significant decrease of total and reduced glutathione, along with a significant increase of different oxidized glutathione forms.ConclusionsThese findings show a relevant in vivo disturbance of glutathione metabolism underlining the contribution of glutathione pool depletion to the redox imbalance in treated cblC patients. Our study may be helpful in addressing future research to better understanding the pathogenetic mechanism of the disease and in developing new therapeutic approaches, including the use of novel vitamin B12 derivatives.

LC-MS/MS method for simultaneous determination on a dried blood spot of multiple analytes relevant for treatment monitoring in patients with tyrosinemia type I.

Tyrosinemia type 1 is caused by deficiency of fumarylacetoacetate hydrolase. The enzymatic defect impairs the conversion of fumarylacetoacetate to fumarate, causing accumulation of succinylacetone which induces severe liver and kidney dysfunction along with mutagenic changes and hepatocellular carcinoma. Treatment is based on nitisinone (NTBC), an enzymatic inhibitor which suppresses succinylacetone production. NTBC, which has dramatically changed the disease course improving liver and kidney functions and reducing risk of liver cancer, causes a side effect of the increase of tyrosine levels. Treatment is therefore based on the combination of NTBC with a protein-restricted diet to prevent the potential toxicity of excessive tyrosine accumulation. Long-term therapy requires a careful monitoring in blood of NTBC levels along with other disease biomarkers, which include succinylacetone, and a selected panel of circulating aminoacids. We have developed a straightforward and fast MS/MS method for the simultaneous determination of NTBC, succinylacetone, tyrosine, phenylalanine, and methionine on a dried blood spot requiring a 2 min run. A single assay suitable for quantitative evaluation of all biochemical markers is of great advance over conventional methods, especially in pediatric patients, since it reduces laboratory costs and blood sampling, is less invasive and particularly suitable for pediatric patients, and allows easier storage and shipping.

Successful pregnancy in a woman with mut− methylmalonic acidaemia

We report on a favourable pregnancy in a woman affected by mut− methylmalonic acidaemia. Under vitamin B12 and carnitine therapy she remained symptom-free throughout pregnancy, labour, delivery and the postpartum period and gave birth to a term, healthy female newborn. At follow-up, the child shows normal somatic and neurocognitive development.

Hypertrophic cardiomyopathy, cataract, developmental delay, lactic acidosis: A novel subtype of 3-methylglutaconic aciduria

Summary3-Methylglutaconic aciduria is the biochemical marker of several inherited metabolic diseases. Four types of 3-methylglutaconic aciduria can be distinguished. In the type I form, accumulation of 3-methylglutaconate is due to deficient activity of 3-methylglutaconyl-CoA hydratase, an enzyme of the leucine degradation pathway. In the other forms, 3-methylglutaconic acid is not derived from leucine but is of unidentified origin, possibly derived from other metabolic pathways, such as mevalonate metabolism. We report five patients, all presenting a severe early-onset phenotype characterized by 3-methylglutaconic aciduria, hypertrophic cardiomyopathy, cataract, hypotonia/developmental delay, lactic acidosis, and normal 3-methylglutaconyl-CoA hydratase activity. This peculiar phenotype, for which a primary mitochondrial disorder is hypothesized, identifies a novel subtype of 3-methylglutaconic aciduria.