Mutations in kelch-like 3 and cullin 3 cause hypertension and electrolyte abnormalities.

Hypertension affects one billion people and is a principal reversible risk factor for cardiovascular disease. Pseudohypoaldosteronism type II (PHAII), a rare Mendelian syndrome featuring hypertension, hyperkalaemia and metabolic acidosis, has revealed previously unrecognized physiology orchestrating the balance between renal salt reabsorption and K(+) and H(+) excretion. Here we used exome sequencing to identify mutations in kelch-like 3 (KLHL3) or cullin 3 (CUL3) in PHAII patients from 41 unrelated families. KLHL3 mutations are either recessive or dominant, whereas CUL3 mutations are dominant and predominantly de novo. CUL3 and BTB-domain-containing kelch proteins such as KLHL3 are components of cullin-RING E3 ligase complexes that ubiquitinate substrates bound to kelch propeller domains. Dominant KLHL3 mutations are clustered in short segments within the kelch propeller and BTB domains implicated in substrate and cullin binding, respectively. Diverse CUL3 mutations all result in skipping of exon 9, producing an in-frame deletion. Because dominant KLHL3 and CUL3 mutations both phenocopy recessive loss-of-function KLHL3 mutations, they may abrogate ubiquitination of KLHL3 substrates. Disease features are reversed by thiazide diuretics, which inhibit the Na-Cl cotransporter in the distal nephron of the kidney; KLHL3 and CUL3 are expressed in this location, suggesting a mechanistic link between KLHL3 and CUL3 mutations, increased Na-Cl reabsorption, and disease pathogenesis. These findings demonstrate the utility of exome sequencing in disease gene identification despite the combined complexities of locus heterogeneity, mixed models of transmission and frequent de novo mutation, and establish a fundamental role for KLHL3 and CUL3 in blood pressure, K(+) and pH homeostasis.

The 4-mg intravenous dexamethasone suppression test in the diagnosis of Cushing's syndrome.

OBJECTIVE: Optimal diagnostic criteria for the 4-mg intravenous dexamethasone suppression test (IVDST) in patients with Cushing's syndrome (CS), compared with normal subjects, have not been established. We evaluated the performance of the 4-mg IVDST for differentiating CS from normal subjects and to define the responses in CS of various aetiologies. DESIGN, SUBJECTS, MEASUREMENTS: Thirty-two control subjects [normal and overweight/obese participants with or without type 2 diabetes) were prospectively studied, and data from 66 patients with Cushing's disease (CD), three with ectopic ACTH syndrome (EAS), 14 with adrenal Cushing's (AC)] and 15 with low probability of CS (LPC) from three tertiary hospitals were retrospectively evaluated. Dexamethasone was infused at 1 mg/h for 4 h. Plasma cortisol and ACTH were measured at -60 min (baseline), -5 min, +3 h, +4 h, +5 h and at +23 and +23.5 h on Day 2. RESULTS: Control subjects (including those with type 2 diabetes) exhibited a marked suppression of cortisol which was maintained until Day 2. Two of 15 patients with LPC had Day 2 cortisol results that overlapped with CS. Patients with CD demonstrated partial suppression, with rebound hypercortisolism on Day 2. Patients with AC and EAS did not suppress cortisol levels. Day 2 cortisol level of >130 nmol/l (or >20% of the baseline) diagnosed CS with 100% sensitivity and 96% specificity. CONCLUSION: While the IVDST allowed complete discrimination between control subjects and CS, 13% of LPC overlapped with CS. Given the small number of EAS, no conclusion can be drawn regarding the utility of this test in the differential diagnosis of CS.

Medications that distort in vitro tests of thyroid function, with particular reference to estimates of serum free thyroxine.

The combination of serum thyroid-stimulating hormone (TSH) with measurement of circulating thyroid hormones greatly improves sensitivity and specificity of thyroid diagnosis, but these assays are not impeccable. Estimation of serum free T4 conveniently accommodates variations in the concentration of thyroxine-binding globulin (TBG), but no current technique reliably reflects the in vivo free T4 concentration in numerous other situations. The effect of circulating competitors that increase T4 and T3 in vivo, in particular, many medications, is under-estimated by current free hormone estimates that involve sample dilution. Non-esterified fatty acids generated during sample storage and incubation can spuriously increase the measured free T4 estimate, especially after in vivo treatment with heparin. These artefacts are unlikely to be overcome by current assay strategies. Total serum T4, corrected for alterations in TBG concentration, gives a more robust estimate of thyroxine concentration than current methods of free hormone estimation and should now be reintroduced as the 'gold standard'.

Barriers in the quest for quality drug information: salutary lessons from TGA-approved sources for thyroid-related medications.

Product information (PI) for thyroid-related medications endorsed by the Therapeutic Goods Administration, as reproduced in the commonly used compilation publications June 2006 MIMS (Monthly index of medical specialties) annual, MIMS Online and the Australian prescription products guide 2006, was evaluated to see whether it reflects contemporary therapeutic practice. Compared with current medical literature, these PI-based sources provide inadequate, inaccurate or outdated therapeutic directives. Examples include: Incorrect advice that thyroxine therapy should always begin at very low dosage. Failure to recommend increased thyroxine dosage early in pregnancy (thus placing the offspring of women being treated for hypothyroidism at risk of impaired fetal brain development). Incorrect and potentially unsafe advice to treat thyrotoxicosis with stable iodide in late pregnancy. Failure to advise serial adjustment of antithyroid drug dosage until after a patient becomes euthyroid (this can result in iatrogenic thyroid dysfunction). Outdated advice that antithyroid drugs are not compatible with breastfeeding. Recent initiatives to upgrade consumer medicine information (CMI) appear to accept PI-based sources as a reliable benchmark for CMI. That inference is not warranted for thyroid-related medications. Accountability for the updating of clinical information in PI needs to be defined, and the process for updating PI may need to be modified. Quality drug information, both PI and CMI, depends on fluent, evidence-based collaboration between suppliers, regulators, prescribers, specialist clinicians and consumers.

Case finding and screening strategies for thyroid dysfunction.

BACKGROUND: A case can be made for routine testing for thyroid dysfunction (TD) in women aged over 50 years once every 5 years when they present for medical care (case finding). This recommendation is based on: (i) the prevalence of TD, predominantly hypothyroidism, (ii) the insensitivity of standard clinical assessment in detecting even overt TD, (iii) the sensitivity of a single test, serum thyroid stimulating hormone (TSH), in identifying both over- and under-function, (iv) the probable adverse consequences of failure to recognize even mild TD, (v) the safety and effectiveness of treatment, and (vi) presumed lack of adverse effect from the testing program. METHODS: A normal serum TSH value has a high negative predictive value in ruling out primary TD; if TSH is abnormal, measurement of serum free thyroxine (T(4)) and further clinical assessment are both required to establish the degree of TD. RESULTS: Case finding identifies more "subclinical" or mild TD (abnormal TSH, normal T(4) and triiodothyronine (T(3))), than overt disease, but a major benefit of widespread testing is the earlier detection and treatment of unsuspected overt disease. There is now evidence that mild TD has adverse consequences and should not merely be regarded as a prognostic indicator, but there is still no consensus whether there is a causal relationship between mild thyroid failure and dyslipidemia. CONCLUSIONS: A case can be made for treatment of both mild thyrotoxicosis and hypothyroidism, but the therapeutic decision is generally simpler for hypothyroidism.