Die biochemiese basis van die gebruik van orotiensuur in die diagnose van aangebore metaboliese defekte
Metabolic screening tests like the ferrichloride- and Benedict tests are commonly used as screening tests for inborn errors of the phenylalanine and carbohydrate metabolic pathways. Just so the excretion of orotic acid could be used as a screening test for a variety of defects. Increased levels of orotic acid in the urine and blood occur as a result of oroticaciduria, but are also abnormally high in cases of increased levels of ammonia. Elevated ammonia levels are found in a variety of defects. including defects of the urea cycle, amino acid-, carbohydrate- and lipid metabolism. If orotic acid can be used as a screening test it will be possible to identify a variety of defects with this technique. In this study an effort was made to determine which defects might be detected with this technique. Levels of orotic acid can potentially increase with any defect. Thus methods had to be applied that could potentially identify the whole spectrum of defects as well as accurately quantify the levels of orotic acid in order to evaluate the screening test. A variety of methods were investigated that could be used for the detection and absolute quantification of orotic acid. Methods for the detection of inborn errors of amino acid- and carbohydrate metabolic pathways as well as organic acid analytical methods has long since been used in the Metabolic Laboratory at Potchefstroom and for this reason it was not necessary to standardise these methods. Since routine analysis for pyrimidines has never been done in the laboratory, and since it had an important role in the verification of the occurrence of orotic acid, this method had to be standardised. For the aim of this study the levels of orotic acid in the urine of more than 1200 patients were determined. Complete diagnostic analysis were performed and a final diagnoses obtained. The values of orotic acid excreted by patients with abnormalities were compared with the values of orotic acid excreted by patients where no abnormalities were present. The effect of medication, age and sex on the excretion of orotic acid was also investigated. By doing this the typical concentrations for orotic acid excretion of different defects could be determined and a protocol for screening suggested.