Genotype Analysis for Diagnosis of Urea Cycle Disorders

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DESCRIPTION (provided by applicant): Urea Cycle Disorders (UCDs) are metabolic diseases disrupting ureagenesis. Unequivocal and rapid diagnosis of UCDs is difficult because hyperammonemia, the primary biochemical phenotype, is not specific to UCDs being observed in broad categories of metabolic deficiencies including fatty acid oxidation defects, lactic acidosis, and organic acidemias. Clinical presentation includes poor feeding, vomiting, and lethargy symptoms leading to misdiagnosis as sepsis. Differential diagnosis of individual urea cycle enzyme defects is complex. The urea cycle contains 6 core genes: N-acetylglutamate synthetase, carbamyl phosphate synthetase, ornithine transcarbamylase (OTC), argininosuccinate synthetase, argininosuccinate lyase, and arginase. OTC deficiency is the most frequently observed UCD and molecular genetic analysis is an established tool for diagnosis. Dye-Binding/High-Resolution Thermal Denaturation (DB/HRTD) is a chemistry that rapidly assesses a PCR product for sequence aberration and was first applied using a single sample instrument the HR-1. A prototype instrument, the LightScanner, allows DB/HRTD to be performed in 96 or 384 well plates enabling concurrent melting and analysis of all samples in a plate. Herein, it is proposed to demonstrate DB/HRTD as a simple means to rapidly assess the 6 core genes of the urea cycle. Specific Aim 1 seeks to validate a preliminary gene-scanning assay for the OTC gene. Specific Aim 2 proposes to design, develop, and provide preliminary validation of a gene-scanning assay for the N-acetylglutamate synthetase gene, defects in which cause NAGS deficiency. Specific Aim 3 proposes to use in situ analysis to unequivocally identify common polymorphisms by means of unlabeled probe chemistry within the context of gene scanning analysis. Specific Aim 4 will demonstrate gene scanning reagents (buffer, dye, dNTPs, oligonucleotides, enzyme) are stabilized by freeze drying and following re-suspension perform in a manner comparable to freshly prepared reagents. Rapid diagnosis of UCD is critical to patient survival. Genetic analysis for urea cycle defects is not widely available yet its utility as a component of the diagnostic regimen is recognized and documented. Stable freeze-dried reagents support rapid genotyping, to strengthen biochemical and clinical evidence in diagnosis of candidate patients. A plate-based system is compatible with block thermalcyclers and existing systems for automated plate loading.