Endocrine Abstracts

JOINT624

Background: Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder commonly caused by mutations in the CYP21A2 gene, leading to 21-hydroxylase deficiency. While genetic testing is pivotal in diagnosing and managing CAH, a substantial proportion of clinically diagnosed cases return negative results, posing challenges for accurate diagnosis and treatment. Understanding the prevalence and underlying causes of these negative results is crucial for advancing diagnostic strategies.

Objectives: This review aims to evaluate the prevalence of negative genetic testing results in clinically diagnosed CAH cases and explore the genetic, technical, and methodological factors contributing to these outcomes.

Methods: A systematic review of 12 studies (1999–2024) encompassing over 2,000 patients was conducted. Data on genetic testing results, prevalence of negative findings, and identified causes were extracted. Studies utilized techniques such as whole-genome sequencing (WGS), multiplex ligation-dependent probe amplification (MLPA), and PCR-based sequencing to investigate mutations in CYP21A2 and related genes.

Results: The prevalence of negative genetic testing in clinically diagnosed CAH cases ranged from 14.4% to 44%. Common causes included:

• Complex genetic architecture: High-sequence homology between CYP21A2 and its pseudogene CYP21A1P, leading to gene conversions and undetectable mutations (Doleschall et al., 2017; Belyeu et al., 2023).

• Technical limitations: Insufficient coverage of testing panels, inability to detect large structural rearrangements, and low sensitivity of standard sequencing methods (Mireia Tondo et al., 2021; Marino et al., 2011).

• Rare or novel mutations: Variants outside commonly tested regions and mild phenotypes contributing to undetected cases (Krone et al., 2013; Ohlsson et al., 1999).

• Population-specific variations: Regional genetic heterogeneity, such as RCCX copy number variations in certain populations (Umaña-Calderón et al., 2021; Dina Fawzi et al., 2023).

Discussion: High-sequence homology and structural complexity in the CYP21A2 gene region remain significant challenges. Emerging techniques like advanced WGS and targeted software tools (e.g., DRAGEN) demonstrate improved sensitivity for small variants and rearrangements. However, access to these technologies is limited in many settings. Novel diagnostic strategies integrating MLPA, PCR, and computational tools are crucial for accurate genotyping in complex cases.

Conclusion: Negative genetic testing in CAH reflects a combination of genetic complexity and technical limitations. Addressing these gaps through advanced diagnostic technologies and comprehensive testing panels is essential for improving diagnostic accuracy, treatment outcomes, and genetic counseling. Future research should focus on refining testing methodologies and exploring the clinical relevance of novel mutations.