Conclusions. Our results showed that conventional in vitro FAO rate assay and acylcamitine profiling in cultured skin fibroblasts could be simplified and performed simultaneously by using the new combined method. Using the new derived parameter, TC, the new method can also reliably detect CUD. Together with molecular studies of ETFA, ETFB and ETFDH genes, the method could detect and confirm a diagnosis of MADD. No definitive case of FAOD was found in a cohort of sixteen SUD cases by the combined method. The new combined method has the potential to be applied as second-line laboratory test for detecting FAOD. (Abstract shortened by UMI.) / First-line laboratory investigation of patients with FAOD is based on some specialized biochemical tests in body fluids including blood/urine carnitine and acylcarnitines, urine organic acids and acylglycines. Further confirmatory tests involve functional assessments of the FAO pathway in cultured skin fibroblasts. The two conventional methods are tritium water release assay for determination of total FAO rate and acylcarnitine profiling for detection of individual FAOD. Based on the basic principles of these two methods, I hypothesized that the total FAO rate assay could be combined with the acylcarnitine profiling if an appropriate substrate and measurement technique were used. In this thesis, I described the development and validation of such assay. In view that the conventional methods cannot reliably detect CUD and MADD, I attempted to test a new derived parameter namely total even-chain acylcarnitines (TC) using the proposed new combined assay for detection of CUD. As mutation analysis of MADD in Chinese patients has not been carried out, a genomic approach was developed to confirm the diagnosis of MADD detected by the new combined assay. Also, the new assay was applied to detect FAOD in a cohort of sudden unexpected death (SUD) Chinese infants. / Mitochondrial fatty acid beta-oxidation (FAO) is a vital process for energy production in most tissues, particularly the skeletal muscle and heart. It also plays an important role to maintain sufficient energy supply through hepatic ketone body formation during fasting and stress. Most fatty acid oxidation disorders (FAOD) may lead to hypoketotic hypoglycaemia, hepatic dysfunction, encephalopathy, skeletal myopathy and cardiomyopathy. / Molecular studies of genomic DNA from five MADD patients in three unrelated Chinese families were performed. Four novel mutations in ETFDH gene were found in two families: one deletion (c.1355delG) and three missense (c.250G>A, c.409C>T and c.1400G>C) mutations. In another family, only one splice site (IVS2+1G>A) mutation in ETFA gene was identified. / The definitive diagnosis in nine CUD patients were made by a very low rates of carnitine uptake (<5% of control) as determined by the conventional radioactive carnitine uptake assay in cultured skin fibroblasts. When using the new combined FAO rate and acylcamitine profiling method, the calculated TC levels of these patients were all below 9.3 nmol/mg protein/96h and were well separated from the control group. At this cutoff value, ROC analysis gave a sensitivity of 100% and specificity of 87.5%, the AUC was 0.993, (p<0.001). Therefore, both conventional radioactive carnitine uptake assay and our new combined assay could be useful for the diagnosis of CUD. / Law, Lap Kay. / Advisers: Christopher Lam Wai Kei; Nelson Tang Leung Sang. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3420. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 177-202). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.