Laboratory Studies
Endocrinologic evaluation
The concentrations of plasma corticotropin, plasma renin activity (recumbent and upright), and aldosterone, as well as those of serum cortisol, testosterone, androstenedione, DHEA, DHEAS, total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides, and fasting glucose and insulin should be recorded in the morning. [45]
Determination of the 24-hour urinary free cortisol (UFC) excretion on 2 or 3 consecutive days is central to the diagnosis, given that patients with Chrousos syndrome demonstrate increased 24-hour UFC excretion in the absence of clinical manifestations suggestive of hypercortisolism. In patients with Chrousos syndrome, the rise in serum cortisol and androgen concentrations, as well as in the 24-hour UFC excretion, varies considerably depending on the severity of impairment of glucocorticoid signal transduction. In most severe cases, serum cortisol and 24-hour UFC concentrations may be, respectively, up to 7- and 50-fold higher than the upper limit of normal range. [45]
Plasma corticotropin concentrations may be normal or high in patients with Chrousos syndrome.
The responsiveness of the HPA axis to exogenous glucocorticoids should also be tested with dexamethasone in patients suspected of having Chrousos syndrome. Increasing doses of dexamethasone (0.3 mg, 0.6 mg, 1 mg, 1.5 mg, 2 mg, 2.5 mg, 3 mg) should be given orally at midnight every other day, and a serum sample should be drawn at 8:00 am the following morning for determination of serum cortisol and dexamethasone concentrations. The concurrent measurement of serum dexamethasone concentrations is suggested in order to exclude the possibility of nonadherence to treatment, increased metabolic clearance, or decreased absorption of this medication. Affected subjects demonstrate resistance of the HPA axis to dexamethasone suppression, which varies depending on the severity of the condition. The dose of dexamethasone required to suppress serum cortisol concentrations by 50% may be up to 7.5-fold higher than that required to achieve the same degree of HPA axis suppression in healthy subjects. [45]
Molecular studies
Thymidine incorporation assays and dexamethasone-binding assays on peripheral blood mononuclear cells in association with sequencing of the hGR gene are necessary to confirm the diagnosis. [28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39] In Chrousos syndrome, the thymidine incorporation assays reveal resistance to dexamethasone-induced suppression of phytohemagglutinin-stimulated thymidine incorporation, while the dexamethasone-binding assays often show decreased affinity of the hGR receptor for the ligand compared with control subjects. [22, 27]
Sequencing of the coding region of the hGR gene, including the intron/exon junctions, reveals mutations or deletions in most but not all patients with Chrousos syndrome. [27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44] Once a structural defect is determined, it is suggested that functional characterization of the mutant receptor should be undertaken in order to determine the molecular mechanisms through which the mutant hGR impairs glucocorticoid signal transduction.
In a study that included 100 patients with bilateral adrenal hyperplasia, increased arterial pressure, and/or hypercortisolism, but no stigmata of Cushing syndrome, Vitellius et al found that 5 of the patients (5%) had novel heterozygous NR3C1 mutations. [46, 47] Thus, Sanger sequencing of the NR3C1 gene is recommended in patients who have clinical features that suggest primary generalized glucocorticoid resistance, or Chrousos syndrome. [47, 48]
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(A) Schematic representation of the structure of the human glucocorticoid receptor (hGR) gene. Alternative splicing of the primary transcript gives rise to the 2 mRNA and protein isoforms, hGR-alpha and hGR-beta. (B) Functional domains of the hGR-alpha. The functional domains and subdomains are indicated beneath the linearized protein structures. AF, activation function; DBD, DNA-binding domain; LBD, ligand-binding domain; NLS, nuclear localization signal. (C) Enlargement of part of the DBD showing the amino acid sequence (single letter codes) of the 2 zinc fingers and the dimerization loop (in bold). The A to T mutation at position 458 that could produce a dimerization defective receptor is shown.
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Nucleocytoplasmic shuttling of the glucocorticoid receptor. Upon binding to the ligand, the activated hGRα dissociates from heat shock proteins (HSPs) and translocates into the nucleus, where it homodimerizes and binds to glucocorticoid response elements (GREs) in the promoter region of target genes or interacts with other transcription factors (TFs), such as activator protein-1 (AP-1), nuclear factor-kappaκB (NF-kappaκB), and signal transducer and activator of transcription-5 (STAT5), ultimately modulating the transcriptional activity of, respectively, GRE- or TFRE-containing genes.
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Location of the known mutations of the hGR gene causing primary generalized glucocorticoid resistance. DBD: DNA-binding domain. GR, glucocorticoid receptor; GREs, glucocorticoid response element; HSP, heat shock protein; LBD, ligand-binding domain; NTD, amino terminal domain; TF, transcription factor; TFRE, transcription factor response element.
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Location of the identified mutations in the hGR gene causing Chrousos syndrome.
