ESPE Abstracts

Background: Primary adrenal insufficiency (PAI) is a rare but life-threatening condition. Its diagnosis is frequently delayed due to its nonspecific and diverse symptoms. The etiology of PAI is heterogeneous and varies among populations.

Objective: The objective of this study was to characterize the clinical and hormonal phenotypes of Thai children with PAI and to determine the underlying genetic defects.

Method: Thai children aged 0-18 years with PAI, who were treated at King Chulalongkorn Memorial Hospital, Bangkok, Thailand between 1999 and 2019, were recruited. Clinical, biochemical, hormonal data, and treatment regimens were collected. Mutation detection was performed using various molecular techniques, including PCR Sanger sequencing of a specific gene for patients with a clinical clue to an underlying gene, whole-exome sequencing for patients with nonspecific clinical profiles, and long-read sequencing with allele-specific PCR for patients with markedly elevated 17-hydroxy progesterone (17-OHP) levels suggesting 21-hydroxylase deficiency (21-OHD) and mutations in CYP21A2.

Results: During the 21-year period, 112 patients with PAI were recruited. The most common manifestations were hyperpigmentation (76%), salt-losing crisis (60%), and ambiguous genitalia (59%). Classic 21-OHD CAH was the most common cause of PAI (86/112; 77%). The female-to-male sex ratio in CAH was 2.4:1, suggesting missed or delayed diagnosis in affected males. The median age at diagnosis was 25 days in salt-wasting form and 2.5 years in simple virilizers. Mutations were successfully identified in 60% (67/112) of patients. Of the 94 patients with CAH, 86 (91.5%) had 21-OHD. Using long-read sequencing, we were able to identify mutations in CYP21A1P/CYP21A2 of all 46 patients with 21-OHD. Chimeric genes were identified in 34.7% (16/46) of patients, and large gene deletions were detected in 30% (14/46) of tested alleles. For rare monogenic causes of PAI, mutations were identified in 90% of tested patients, which were NR0B1 (6/26, 23%), ABCD1 (4/26, 15%), StAR (3/26, 12%), CYP17A1 (3/26, 12%), CYP11B1 (2/26, 8%), and CYP11A1 (1/26, 4%). Two novel mutations were identified, including p.Asn482Tyr and p.Ser98Leu in the CYP11A1 gene.

Conclusion: This study characterized the phenotypic and genotypic spectra of Thai children with PAI. Comprehensive genetic testing elucidates the etiologies of most PAI patients. Long-read sequencing with allele-specific PCR is a new combined technique that could identify 100% of CYP21A2 variants. Excluding CAH, NR0B1 mutations are the most common genetic cause of rare forms of PAI in the Thai population.