Diagnostic dilemma of patients with methylmalonic aciduria: Experience from a tertiary care centre in Pakistan

Objective: To determine the frequency of disorders leading to methylmalonic acidurias. Methods: This cross-sectional study was conducted from January 2013 to April 2016 at the Aga Khan University Hospital, Karachi, and comprised patients diagnosed with methylmalonic acidurias based on urine organic acid analysis. Clinical history and biochemical data was collected from the biochemical genetics laboratory requisition forms. Organic acid chromatograms of all the subjects were critically reviewed by a biochemical pathologist and a metabolic physician. For assessing the clinical outcome, medical charts of the patients were reviewed. SPSS 19 was used for data analysis. Results: Of the 1,778 patients 50(2.81%) were detected with methylmalonic acidurias. After excluding patients with non-significant peaks of methylmalonic acidemia, 41(2.31%) were included in the final analysis. Of these, 20(48.7%) were females, while the overall median age was 11.5 months (interquartile range: 6-41.5). On stratification by type of disorders leading to methylmalonic acidurias, 9(22%) had methylmalonic acidemia, 12(29%) had Cobalamin-related remethylation disorders, nonspecific methylmalonic acidurias in 16(39%), while 2(5%) each had succinyl coenzyme A synthetase and Vitamin B12 deficiency. respectively. Conclusion: Screening tests, including urine organic acid, provided valuable clues to the aetiology of methylmalonic acidurias

System efficiency for AC vs. DC distribution paradigms: a comparative evaluation

The birth of electricity witnessed “the battle of currents” between AC and DC as a medium of power transfer. AC won the battle in the first place because of its ability to transform voltage levels. However, with the development of power electronic converters (PECs), DC is striking back. Most of the electronic loads in our conventional AC-based homes are DC by nature. Moreover, the modern concept of energy-efficient variable speed drive (VSD) based loads, i.e. DC-inverter based air-conditioners and refrigerators, require a DC link for their operation. The driving component of all such loads is the PEC. The operational efficiency of PECs depends on the loading which varies throughout the day. This paper presents a mathematical model based on a bottom-up approach to the comparative efficiency analysis of AC and DC distribution systems considering daily load variation. Two topologies are presented where AC and DC distribution systems are compared in terms of efficiency. The first topology (T1) defines a separate/independent converter for each load, whereas in the second topology (T2) loads of a particular class are lumped and driven by a single converter. The results present DC distribution better than AC distribution with an efficiency advantage of 2.28% and 1.57% for T1 and T2, respectively