Clinical presentation, laboratory findings, and genetic features indicated the diagnosis of CAH resulting from 11β-OHD in our patient, which appeared to be a compound heterozygote for two novel mutations in the CYP11B1 gene.
11β-hydroxylase, one of the cytochrome P-450 enzymes, consists of 503 amino acids [12]. To date, a cluster of mutations have been reported, some of which affect the spatial conformation of 11β-hydroxylase to varying degrees, in particular to maintain the conformation of the key region of the enzyme activity [13,14,15,16,17]. Some mutations could change the reading frame, resulting in production of the wrong protein. If the premature termination appears in advance, the protein expression is terminated prematurely, causing the corresponding functional domain of the protein to change or disappear and the enzyme activity to be lost, accordingly [18,19,20,21].
In this study, we identified a novel mutation, c.1094_1120delTGCGTGCGGCCCTCAAGGAGACCTTGC in exon 6, which resulted in the deletion of 9 amino acids at position 364_372 (p.364_372del). CYP11B1, a cytochrome P-450 enzyme, uses heme as a prosthetic group to catalyze redox reactions [22]. The three-dimensional structure of the protein shows that I-, K-, and L-helixes contain a highly conserved heme-binding area [22]. The amino acid residues 364_372 constitute the putative K-helix of the CYP11B1 model [22]. The deletion of amino acid residues 364_372 may have resulted in defection of the K-helix. The side chain of R366 faces toward the protein surface, maintaining a positive surface charge. Additionally, the positive surface charge is involved in the CYP-Adx interaction, which is fundamental for CYP11B1 function [14]. A368 was located in a hydrophobic environment and interacted with the hydrophobic side chains of the amino acid residues V336 and L340 located in the J-helix [17]. The change in A368 resulted in a disorientation of the J-helix, I-helix, or K-L loop, containing a meander region and C450 coordinating the heme iron [17]. Changing this structure’s orientation resulted in substantial changes of both the protein conformation and the heme group orientation relative to the enzyme [17]. E371 at the end of the K-helix might be located in the conserved central core of the P450 enzymes, and the protein domain around the conserved central core could be of fundamental importance [15]. We speculate that p.364–372 del could decrease or abolish CYP11B1 activity by preventing the formation of the K-helix, which in turn would affect the tertiary structure of the protein.
In addition, we also identified c.1440–1447 delins TAAAAG in exon 9, leading to the loss of original stop codon and resulting in an elongated protein. L487-A501 is conserved in humans, rats, and mice [22]. One study reported that the last 10 amino acids in the C-terminal region of the CYP11B1 gene have little effect on CYP11B1 function [23]. It is not clear whether the C-terminal protein elongation will affect the three-dimensional structure of the enzyme and thus reduce its activity. We speculate that the mutation of c.1440_1447delinsTAAAAG in exon 6 could be the primary cause of the 11β-OHD in our patient. Combining in vitro expression studies with protein structure analysis is a powerful means of providing new insights in the understanding of structural–functional relationships.
The patient in this article took an unnecessarily high dose of dexamethasone over a long period without regular follow-up or dose adjustment, and he ultimately developed iatrogenic Cushing’s syndrome and reduced final height. The treatment of 11β-OHD is generally identical to that of 21-OHD. Glucocorticoid doses should be adjusted to reduce the risk of iatrogenic Cushing’s syndrome and growth impairment, but stress doses of glucocorticoids are necessary in cases of acute illness [24, 25]. Monitoring with plasma DOC and plasma renin activity can be helpful. Additional antihypertensive treatment may be required if blood pressure remains elevated, despite optimal glucocorticoid treatment. Supplemental treatments to maintain the balance of electrolytes and blood pressure include spironolactone, amiloride, and calcium channel blockers [7, 24]. Since the renin-angiotensin system is suppressed in these patients, angiotensin-converting enzyme inhibitors and angiotensin receptor II blockers should be avoided.
The management of CAH can be complicated by iatrogenic Cushing’s syndrome, inadequately treated hyperandrogenism, or both. Patients treated with supraphysiological doses of glucocorticoids not only experienced slowed growth but could also exhibit the signs and symptoms of iatrogenic Cushing’s syndrome. Thus, we emphasized the importance of clinical follow-up. Close clinical monitoring of symptoms and signs, growth and development, and laboratory results are essential to optimize treatment outcomes.
In conclusion, our findings demonstrated the presence of the 11β-OHD phenotype with two novel pathogenic mutations of the CYP11B1 gene in a Chinese patient. On the basis of our results, the outcome of this study has paved the way for a more efficient diagnosis and genetics counseling for diagnosis of patients with this disorder in China. Further research is required, however, to determine in vitro expression studies and protein structure analysis that may affect 11β-hydroxylase activity.