EMQN Best Practice Guidelines for Molecular Genetic Testing and Reporting of 21-Hydroxylase Deficiency

The EMQN best practice guidelines for molecular genetic testing and reporting of 21-hydroxylase deficiency (21-OHD) were developed based on extensive experience from a European-wide external quality assessment scheme involving about 60 laboratories from Europe, the USA, and Australia. These guidelines aimed to ensure quality in diagnostic molecular genetic laboratories, focusing on CYP21A2 genotyping for differential diagnosis, carrier detection, and genetic counseling. They emphasized the use of appropriate methodologies, such as sequencing methods and MLPA, while addressing their limitations and analytical accuracy. The guidelines also covered the classification of variants and the standardization of reporting genotyping results, providing a comprehensive list of common and previously unreported CYP21A2 variants.