CBG Santiago: A Novel CBG Mutation

Abstract

Context: Corticosteroid-binding globulin (CBG; SERPIN A6) gene mutations are rare; only four mutations have been described, often in association with fatigue and chronic pain, albeit with incomplete penetrance. Patient: We report a kindred with a novel SERPINA6 mutation. The proband, a 9-yr-old male, had excessive postexertional fatigue, weakness, and migraine. Main Outcome Measures and Results: Investigations revealed low morning and ACTH-stimulated peak cortisol levels. SERPIN A6 sequencing detected a novel exon 2 single base deletion (c.13delC) leading to a frameshift generating a stop codon within the signal peptide coding region (p.Leu5CysfsX26) and 50% reduced CBG levels in heterozygotes. The patient’s father and two sisters share the mutation. Symptom expression within the family may have been modified by a polymorphic CBG allele (c.735G T). Exogenous hydrocortisone had no effect on the fatigue. Conclusion: This report documents the fifth CBG gene mutation in humans and the second causing major effects on CBG levels. Individuals with low CBG levels may be misdiagnosed as having secondary hypocortisolism. The association with fatigue and idiopathic pain is again noted and may relate to altered stress system function. Variability of the phenotype may relate to other genetic variations of the CBG gene or environmental factors.