Exonic duplication of the OTC gene by a complex rearrangement that likely occurred via a replication-based mechanism: a case report

Hemizygous deletion in the OTC gene results in ornithine transcarbamylase deficiency: A case report

BACKGROUND

Ornithine transcarbamylase deficiency (OTCD) is a common ornithine cycle disorder, and OTC gene variation is the main pathogenic factor of this disease. This study explored and validated a variant in the OTC gene.

CASE SUMMARY

The neonate exhibited high blood ammonia, lactic acid, and homocysteine levels on the fifth day after birth. A novel deletion variant in the OTC gene [NM_000531.5, c.970_979delTTCCCAGAGG, p.Phe324GlnfsTer16] was uncovered by exome sequencing. The variant caused a protein-coding frameshift and resulted in early translation termination at the 16^th amino acid after the variant site.

CONCLUSION

Our results provide a novel pathogenic variant in OTC and related clinical features for further OTCD screening and clinical consultation.

The Application of Next-Generation Sequencing (NGS) in Neonatal-Onset Urea Cycle Disorders (UCDs): Clinical Course, Metabolomic Profiling, and Genetic Findings in Nine Chinese Hyperammonemia Patients

During Jan. 2016–Dec. 2019, nine Chinese patients from eight unrelated families were diagnosed with neonatal-onset UCDs by targeted panel sequencing or whole-exome sequencing (WES). Their clinical manifestations, biochemical features, 180-day-age outcomes, and molecular genetic characteristics were reviewed retrospectively. NGS-based tests revealed 7 patients diagnosed with ornithine transcarbamylase deficiency (OTCD) and 2 with carbamoylphosphate synthetase I deficiency (CPS1D). The spectrum of the clinical presentation of nine affected individuals progressed from unspecific symptoms like poor feeding to somnolence, coma, and death. All patients presented with an acute hyperammonemia. The most robust metabolic pattern in OTCD was hyperglutaminemic hyperammonemia with high concentration of urine orotic acid, and it was reported in six patients. Of ten variants found on the OTC gene and CPS1 gene, 3 were novel: (c.176T>C (p.L59P)) in the OTC gene, c.2938G>A (p.G980S) and c.3734T>A (p.L1245H) in the CPS1 gene. There was a high mortality rate of 77.78% (7/9) for all the defects combined. An OTC-deficient male and a CPS1-deficient female survived from episodes of hyperammonemia. Although prompt recognition of UCD and the use of alternative pathway therapy in addition to provision of appropriate nutrition and dialysis improved survival, the overall outcomes for the neonatal-onset type are poor in China.