Although there a well-known correlation in genotype and phenotype, patients with 21-OHD caused by severe pathogenic variants have better correlation, whereas inconsistencies are more common in the presence of milder variants. This study aimed to evaluate CYP21A2 genotyping and reveal the genotype-phenotype correlation in children diagnosed with 21-OHD in the South-eastern Anatolia region, where ethnic diversity and consanguineous marriage rates are high. The patients were divided into three groups: salt wasting (SW), simple virilizing (SV) and non-classical (NC). Pathogenic variants of the CYP21A2 gene were classified into six groups based on predicted 21-hydroxylase activity: null-A-B-C-D-E. CYP21A2 genotyping was performed by sequence-specific primer and sequenced with next generation sequencing (NGS), and the expected phenotypes were compared to the observed phenotypes. The overall genotype-phenotype concordance was found to be 73.1% (68/93). The expected concordance with the SW form of the null (n = 12) and A (n = 51) groups is 91.6% and 88.2%, respectively. While the percentage of the expected clinical form of SV in patients in group B (n = 5) was 80%, the concordance for the expected clinical form of NC for group C (n = 25) was not strong enough (32%). This study demonstrates that children with 21-hydroxylase deficiency show a good correlation between severe pathogenic variants and predicted clinical phenotypes; however, the correlation is not strong enough between milder variants. The discrepancies could have resulted from the complex characteristics of 21-OHD genotyping and the limitations of using NGS alone without integrating with other comprehensive methods.

Congenital Adrenal Hyperplasia (CAH) due to 21-hydroxylase deficiency (21-OHD CAH) is an autosomal recessive disorder resulting from pathogenic variants in the CYP21A2 gene. The disorder exhibits variable clinical severity, with the classical form manifesting as salt-wasting crisis in neonates, while inducing ambiguous genitalia in females and precocious puberty in males through simple virilization. Identifying at-risk couples during the preconception stage holds significance for optimizing reproductive choices. This study included 204 unrelated preconception individuals undergoing carrier screening. A robust molecular approach was devised for rapid detection of nine prevalent CYP21A2 pathogenic variants, utilizing Amplification-Refractory Mutation System (ARMS) PCR and mass spectrometry (MS) genotyping. Complementary quantitative real-time PCR (qPCR) and PCR-based Restriction Fragment Length Polymorphism (PCR-based RFLP) assays were employed for comprehensive gene deletion analysis. The concordance of pathogenic variant detection between ARMS-PCR and MS, as well as the consistency observed in molecular insights from qPCR and PCR-based RFLP, fortified the accuracy of our methodologies. Our combined method could detect common pathogenic variants and large gene deletions with high concordance between ARMS-PCR, MS genotyping, qPCR, and PCR-based RFLP assays. Remarkably, two carriers exhibited significant large-scale deletions, while another manifested a carrier state due to minor-scale gene conversion. The estimated carrier frequency in our cohort using these methods was approximately 1 in 65 individuals. The methods used for 21-OHD CAH carrier screening offer a reliable, swift, and cost-effective approach for detecting common pathogenic variants and large deletions. Despite some limitations, such as the inability to detect all rare mutations, the techniques provide a practical solution for carrier screening, with an estimated carrier frequency of 1 in 65 in our study population. These findings support the potential adoption of these methods in national carrier screening programs, offering a practical balance between efficiency and affordability.

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disease that manifests clinically in varying forms depending on the degree of enzyme deficiency. CAH is most commonly caused by 21-hydroxylase deficiency (21OHD) due to mutations in the CYP21A2 gene. Whereas there is a spectrum of disease severity, 21OHD is generally categorized into 3 forms. The classic form encompasses salt-wasting and simple virilizing CAH and the least affected form is termed nonclassic CAH. The classic form of 21OHD occurs in ∼1 in 16 000 births with the most severe salt-wasting cases presenting in the neonatal period with cortisol and aldosterone deficiencies and virilization of external female genitalia. Cortisol deficiency removes normal feedback on the hypothalamic-pituitary-adrenal axis leading to elevations in ACTH and adrenal androgen levels, which often accelerate skeletal maturation, leading to premature epiphyseal growth plate closure. Additionally, supraphysiologic doses of glucocorticoids are necessary to suppress androgen levels, adversely affecting final adult height. This paper highlights a brief history of 21OHD and provides an overview of the genetic basis and pathophysiology of 21OHD.

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disease caused by the deficiency of one of the enzymes involved in cortisol synthesis. Between 90% and 99% of cases of CAH are caused by 21-hydroxylase deficiency (21-OHD) caused by mutations in CYP21A2. Although 21-OHD has been historically divided into classical and non-classical forms, it is now thought to show a continuous phenotype. In the classical form, the external genitalia in females becomes virilized to varying degrees. If the disease is not recognized, salt wasting crises in the classical form may threaten life in neonates. Children experience accelerated somatic growth, increased bone age, and premature pubic hair in the simple virilizing form of classical 21-OHD. Female adolescents may present with severe acne, hirsutism, androgenic alopecia, menstrual irregularity or primary amenorrhea in the non-classical form. Diagnosis of CAH is made by clinical, biochemical and molecular genetic evaluation. In cases of 21-OHD, the diagnosis is based on the 17-hydroxyprogesterone (17-OHP) level being above 1000 ng/dL, measured early in the morning. In cases with borderline 17-OHP levels (200-1000 ng/dL), it is recommended to perform an adrenocorticotropic hormone (ACTH) stimulation test. Genotyping in cases with CAH should be performed if the adrenocortical profile is suspicious or if the ACTH stimulation test cannot be performed completely. After diagnosis, determining the carrier status of the parents and determining which parent the mutation was passed on from will help in interpreting the genetic results and determining the risk of recurrence in subsequent pregnancies.

Despite the high sensitivity of neonatal screening in detecting the classical form of congenital adrenal hyperplasia due to 21-hydroxylase deficiency, one of the unclear issues is identifying asymptomatic children with late onset forms. The aim of this nationwide study was to analyse the association between genotype and screened level of 17-hydroxyprogesterone in patients with the late onset form of 21-hydroxylase deficiency and to quantify false negativity. In the Czech Republic, 1,866,129 neonates were screened (2006-2022). Among this cohort, 159 patients were confirmed to suffer from 21-hydroxylase deficiency, employing the 17-hydroxyprogesterone birthweight/gestational age-adjusted cut-off limits, and followed by the genetic confirmation. The screening prevalence was 1:11,737. Another 57 patients who were false negative in neonatal screening were added to this cohort based on later diagnosis by clinical suspicion. To our knowledge, such a huge nationwide cohort of false negative patients has not been documented before. Overall, 57 patients escaped from neonatal screening in the monitored period. All false negative patients had milder forms. Only one patient had simple virilising form and 56 patients had the late onset form. The probability of false negativity in the late onset form was 76.7%. The difference in 17-hydroxyprogesterone screening values was statistically significant (p<0.001) between severe forms (median 478.8 nmol/L) and milder (36.2 nmol/L) forms. Interestingly, the higher proportion of females with milder forms was statistically significant compared with the general population. A negative neonatal screening result does not exclude milder forms of 21-hydroxylase deficiency during the differential diagnostic procedure of children with precocious pseudopuberty.