OTC gene duplication as the possible cause of massive hyperammonaemia with a fatal prognosis.

Ornithine transcarbamylase (OTC) deficiency is the most common urea cycle disorder. It may occur due to various changes to the OTC gene located on the X chromosome. Many sequence variants in the OTC gene result in different severity and require different types of molecular testing. We present a familial case of hyperammonemia possibly caused by the small CNV (duplication) within exon 2 of the OTC gene that was not detected by standard sequencing methods. In this case, the knowledge of the underlying molecular changes to the gene results in an appropriate approach to future sibling screening. Collecting more data, especially regarding rare variants of genetic disorders, is essential as it will help to create the best diagnostic-therapeutic path in prenatal and neonatal care in the future. Early diagnosis and treatment can lead to a better prognosis, and this case emphasizes the importance of understanding genetic changes in OTC deficiency.