['Ornithine transcarbamylase (OTC) deficiency is the most common inborn error of urea metabolism that can lead to hyperammonemic crises and orotic aciduria. To date, a total of 341 causative mutations within the OTC gene have been described. However, in about 20% of the patients with enzymatically confirmed OTC deficiency no mutation can be detected when sequencing of genomic DNA analyzing exons and adjacent intronic segments of the OTC gene is performed.', 'Standard genomic DNA analysis of the OTC gene in five consecutive patients from five families revealed no mutation. Hence, liver tissue was obtained by needle sampling or open biopsy and RNA extracted from liver was analyzed.', 'Complex rearrangements of the OTC transcript (three insertions and two deletions) were found in all five patients.'] Does analysis of mRNA transcripts improve the success rate of molecular genetic testing in OTC deficiency?