Marta Simões

Coenzyme Q10 deficiency in mitochondrial DNA depletion syndromes

We evaluated coenzyme Q₁₀ (CoQ) levels in patients studied under suspicion of mitochondrial DNA depletion syndromes (MDS) (n=39). CoQ levels were quantified by HPLC, and the percentage of mtDNA depletion by quantitative real-time PCR. A high percentage of MDS patients presented with CoQ deficiency as compared to other mitochondrial patients (Mann-Whitney-U test: p=0.001). Our findings suggest that MDS are frequently associated with CoQ deficiency, as a possible secondary consequence of disease pathophysiology. Assessment of muscle CoQ status seems advisable in MDS patients since the possibility of CoQ supplementation may then be considered as a candidate therapy.

Secondary coenzyme Q10 deficiencies in oxidative phosphorylation (OXPHOS) and non-OXPHOS disorders.

We evaluated the coenzyme Q₁₀ (CoQ) levels in patients who were diagnosed with mitochondrial oxidative phosphorylation (OXPHOS) and non-OXPHOS disorders (n=72). Data from the 72 cases in this study revealed that 44.4% of patients showed low CoQ concentrations in either their skeletal muscle or skin fibroblasts. Our findings suggest that secondary CoQ deficiency is a common finding in OXPHOS and non-OXPHOS disorders. We hypothesize that cases of CoQ deficiency associated with OXPHOS defects could be an adaptive mechanism to maintain a balanced OXPHOS, although the mechanisms explaining these deficiencies and the pathophysiological role of secondary CoQ deficiency deserves further investigation.

Frontotemporal dementia and mitochondrial DNA transitions

Frontotemporal dementia (FTD) is the second most common type of primary degenerative dementia. Some patients present an overlap between Alzheimers disease (AD) and FTD both in neuropathological and clinical aspects. This may suggest a similar overlap in physiopathology, namely an involvement of mitochondrial DNA (mtDNA) in FTD, as it has been associated to AD. To determine if mtDNA is involved in FTD, we performed a Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) analysis, specific to mtDNA NADH Dehydrogenase subunit 1 (ND1) nucleotides 3337-3340, searching for mutations previously described in Parkinsons and AD patients. We could identify one FTD patient with two mtDNA transitions: one already known (3316 G-to-A) and another unreported (3337 G-to-A). Additionally, mitochondrial respiratory chain complex I activity was reduced in leukocytes of this patient (36% of the control mean activity). To our knowledge, this is the first report of mtDNA variants in FTD patients.

Nonketotic Hyperglycinemia : A Cause of Encephalopathy in Children

Nonketotic hyperglycinemia is a rare metabolic disorder with severe, frequently fatal, neurologic manifestations. Reliable and accurate diagnosis depends on careful interpretation of laboratory findings. The clinical suspicion should lead to determination of glycine in plasma and cerebrospinal fluid. Amino acid analysis presents diagnostic values for classic nonketotic hyperglycinemia, but it also should be performed in suspected cases of atypical nonketotic hyperglycinemia and in children with seizures, failure to thrive, behavior problems, and uncoordinated movements. Clinical assessment should be reinforced by demonstration of elevated cerebrospinal fluid–to–plasma glycine ratio. Confirmatory diagnosis requires enzymatic and genetic investigation of glycine cleavage system. An early diagnosis, though not affecting clinical outcome, allows proper genetic counseling, with the possibility of prenatal diagnosis. We report 3 cases of nonketotic hyperglycinemia, 2 typical neonatal and 1 atypical, diagnosed in Pediatric Hospital of Coimbra, Portugal, and investigated at Laboratory of Biochemical Genetics in 2004 to 2010 (incidence 1:47 455; prevalence 1:782 951).

Mitochondrial DNA 8993T>G mutation in a child with ornithine transcarbamylase deficiency and leigh syndrome: an unexpected association.

MC, female, is the third child of a nonconsanguineous Portuguese couple, born after an uneventful pregnancy and delivery. A positive family history of ornithine transcarbamylase deficiency, associated with the IVS8+1 G>A mutation in the ornithine transcarbamylase gene, prompted prenatal diagnosis with identification of the same mutation in the proband. During an episode of Klebsiella pneumoniae sepsis at 1.5 months of age, lactic acidosis and moderate hyperammonemia were noticed. After a short asymptomatic period, progressive neurologic symptoms, with normal ammonemia, persistent hyperlactacidemia, and typical lesions in brain computed tomography (CT) scan led to a diagnosis of Leigh syndrome. Mitochondrial respiratory chain complex V was reduced in the liver. The mtDNA 8993T>G mutation was identified in the liver, muscle, and blood (82%-87% heteroplasmy). She died at 6 months of age. This case represents a benign phenotype of ornithine transcarbamylase deficiency, associated with a severe mitochondrial respiratory chain disorder due to an mtDNA pathogenic mutation.

In silico analysis for predicting pathogenicity of five unclassified mitochondrial DNA mutations associated with mitochondrial cytopathies' phenotypes

Mitochondrial DNA (mtDNA) mutations have been assigned as a major cause of genetic disease. When a novel sequence variation is found, it is necessary to evaluate its functional impact, usually requiring functional molecular studies. Given the fact that this approach is difficult to put in practice in a routine basis, it is possible to take advantage of the in silico tools available and predict protein/RNA structure changes and therefore pathogenicity. Here, we describe the characterization of five undescribed mtDNA variants, upon detection of 23 unclassified alterations at Laboratory of Biochemical Genetics, from 2004 to 2014. Those five sequence variations are located in protein-coding genes, in five patients with a diverse range of mitochondrial respiratory chain disease phenotypes including encephalopathy, optic neuropathy, developmental delay, deafness and epilepsy. According to the prediction established by in silico analysis using tools to predict structure and function changes (ClustalW2®, PolyPhen-2®, SIFT®, MutationAssessor®, PredictProtein®, Provean®, I-TASSER®, Haplogrep®), from the 23 variants analyzed, the five described are potentially pathogenic. This approach is inexpensive and compatible with a rapid first line response to clinical demanding, contributing to a more rationale genetic diagnosis concerning novel mutations and to clarify the mtDNA involvement in these pathologies.

Citrullinemia stimulation test in the evaluation of the intestinal function

BACKGROUND Citrullinemia is been reported as a quantitative parameter of the enterocyte mass and function. AIM The objective of this research is to analyse the value of fasting and stimulated citrullinemias in the intestinal function evaluation. METHODS A case-control study was undertaken, including 11 patients with short bowel syndrome, 13 patients submitted to malabsorptive bariatric surgery and 11 healthy controls. Plasma levels of amino acids were determined, before and after a stimulation test with oral Lglutamine, by ion exchange chromatography. RESULTS Citrullinemia was inferior in short bowel patients (28,6 ± 11,3 versus 35,5 ± 11 in operated obese versus 32,2 ± 6,6 μmol/L in controls; n.s.) and lower than 25,5 μmol/L in 54,5% of them (versus 16,7%; p = 0,041; accuracy = 74%; odds ratio = 3, 95%CI 1,2-7,6). ΔCitrullinemia80 (relative variation of citrullinemia at the 80th minute of test) was lower in short bowel patients; its diagnostic accuracy was similar to baseline citrullinemia and also not significant. ΔCitrullinemia80 revealed a high predictive capacity of a short bowel inferior or equal to 50 cm (auR.O.C. = 82,3%; 95%CI 61,7-102,8; p = 0,038). CONCLUSIONS In short bowel syndrome context, citrullinemia stimulation test with oral L-glutamine is feasible and it may improve the predictive capacity of severity. Further investigation is required to determine its clinical relevance and applicability.

Mind the Gap: education inequality at the regional level in Portugal, 1986-2005

Portugal stands as one of the most unequal countries in terms of income among the developed countries. Over the period 1980-2005, income inequality kept high, fostered mainly by a monotonic increase in earnings inequality. Given the close link between education and earnings, it is of major importance to study the distribution of education. This paper examines the distribution of education at the regional level in Portugal between 1986 and 2005. Our results indicate that education inequality decreased for the whole country as the average education level of the workforce rose, over the sample years. This finding does not apply at the regional level however, with several districts initially poor in terms of education exhibiting an increase in education inequality. The evidence also supports the existence of a Kuznets curve of education: as the average level of education rises, education inequality first increases, and, after reaching a peak at 5.13 years of schooling, starts declining.

Identification of a novel deletion in SURF1 gene: Heterogeneity in Leigh syndrome with COX deficiency

Leigh syndrome (LS) is a rare, progressive neurodegenerative mitochondrial disorder of infancy. It is a genetically heterogeneous disease. The mutations in SURF1 gene are the most frequently known cause. Here two cases of LS likely caused by SURF1 gene variants are reported: a 39-year-old male patient with a novel homozygous deletion (c.-11_13del), and a case of a 6-year-old boy with the same deletion and a nonsense mutation (c.868dupT), both in heterozygosity. Blue native PAGE showed absence of assembled complex IV. This is the first report of a variant that may abolish the SURF1 gene initiation codon in two LS patients.

A quantile regression analysis of growth and convergence in the EU: potential implications for Portugal

This paper applies a quantile regression approach to examine the growth and convergence process of fourteen EU member states over the period 1986-2009. From the results of the estimation of an accounting growth regression we conclude that an increase in the weight of the non-tradables sector and a loss of (price) competitiveness are especially harmful for growth for under-performing countries, while these benefit the most from physical capital accumulation and are less negatively affected by an increase in government consumption. Additionally, technological convergence is felt less strongly by low-growth member states. The variables retained are robustly related to growth at all quantiles, but the quantitative importance of the respective coefficients differs across quantiles in some cases. Given the changes in growth rhythms that Portugal recorded throughout the period under analysis, we derive some potential implications from these results for a better understanding of the Portuguese growth and convergence process after European integration. Our findings suggest that, given the growth deceleration that the Portuguese economy has been experiencing since the late 1990s, policies to enhance growth should pay more attention to promoting competitiveness and changing the specialization pattern away from the non-tradables sectors, as well as to increasing investment.