Graves' disease of the beta cell: glucose dysregulation due to islet-cell stimulating antibodies

HbA1c: an independent risk factor for dysthyroid optic neuropathy

Background

We aimed to explore the frequencies of islet β-cell autoantibodies and insulin resistance (IR) in thyroid-associated ophthalmopathy (TAO) and identify specific diabetes mellitus (DM) indicators as early predictors for dysthyroid optic neuropathy (DON).

Methods

Ninety-eight TAO patients (57 DON and 41 non-DON patients) and 48 healthy control (HC) participants were recruited for this prospective cross-sectional study. Serum thyroxine, serum thyroid autoantibodies, serum humoral immune markers against islet β-cell, fasting plasma glucose (FPG), fasting serum insulin (FINS), fasting c-peptide (FCP), and glycosylated hemoglobin A1 (HbA1c) were measured. Logistic regression analysis was used to evaluate the correlation of patients' age, body mass index (BMI), FPG, HbA1c, and related indexes of islet β-cell function to the occurrence of DON.

Results

The DON group had higher FPG (P<0.001, 0.016) and HbA1c (P<0.0001, P<0.001) levels than the HC and non-DON groups. The homeostasis model assessment (HOMA)-IR level was the highest in the DON group (HC 2.15 ± 0.89, non-DON 2.41 ± 1.24, and DON 2.82 ± 2.65), while the HOMA-β level was the lowest (HC 101.8 ± 44.75%, non-DON 102.9 ± 54.61%, and DON 88.29 ± 52.75%), with no significant differences (P=1, P>0.05). On univariate analysis, age (P=0.006), BMI (P=0.022), history of steroid use (P=0.014), FPG (P=0.013), and HbA1c (P=0.001) levels were significantly associated with the presence/absence of DON. In addition, after adjusting for potential confounds, the HbA1c level was an independent factor associated with DON (P=0.009, OR=4.012).

Conclusions

HbA1c is an independent risk factor for DON. Given the interconnected link between thyroid dysfunction and DM, the use of HbA1c as a potential biomarker for DON warrants further investigation.

Autoimmune hypoglycemia

Autoimmune hypoglycemia is a rare but fascinating syndrome of hypoglycemia caused by the interaction of endogenous antibodies with insulin or the insulin receptor. Awareness of autoimmune hypoglycemia is important because the syndrome may produce severe neuroglycopenic symptoms and may be confused with the presence of an insulinoma. A correct diagnosis is important to avoid unnecessary surgical intervention in patients who are best treated with conservative support, watchful waiting, or in some cases, immunosuppressive therapy.

Facilitation of the growth promoting effect of growth hormone (GH) by an antibody to methionyl-GH

Despite the development of antibodies to methionyl growth hormone in a child with hypopituitarism, the patient grew at a rapid rate on low doses of somatotropin. Serum immunoglobulins from this patient stimulated the growth of Nb2 lymphoma cells in vitro in samples obtained within 48 hours after the last dose of growth hormone, while samples obtained several weeks after an injection of methionyl growth hormone did not. Immunoglobulins from normal subjects or from hyposomatotropic patients being treated with methionyl growth hormone who had not developed antibodies did not stimulate Nb2 lymphoma cell growth. We suggest that the antibodies to methionyl growth hormone in this child served as a reservoir for exogenous growth hormone or facilitated the interaction of growth hormone with the prolactin receptor on the Nb2 lymphoma cell.

Characterization of insulin autoantibodies in a patient with autoimmune hypoglycemia

A 60-year-old man referred because of hypoglycemic bouts was found to have insulin autoantibodies. Total plasma insulin was as high as 1.44 nmol/l. Both plasma free insulin and C-peptide were in the normal range. The indirect immunofluorescence technique showed positivity for antinuclear antibodies. The T-lymphocyte populations in the peripheral blood were normal. When serum binding capacity for pork insulin was measured, antibodies binding pork insulin were not detected. The patient's serum bound 125I-insulin. The binding protein was identified to be an immunoglobulin G. The kinetics of dissociation, studied by the Scatchard analysis of the autoantibody, showed a curvilinear plot, which was analyzed in two components. Cold human insulin was able to compete with 125I-insulin for the antibody binding site (I.C.50 = 1.35 nmol/ml). These antibodies were apparently not associated with antibodies directed against the insulin receptor.

Hypoglycaemia in the adult

Hypoglycaemia is a relatively common cause for referral of patients to the accident and emergency departments of hospitals but most of it is iatrogenic. Occasionally, however, hypoglycaemia is due to any one of up to a hundred different disorders. In some, hypoglycaemia is the cause of intermittent neuroglycopenic symptoms that lead to their referral to medical outpatients for investigation. Only the most important are discussed here. Hyperinsulinism due to abnormal beta-cell function is an uncommon but important cause of spontaneous hypoglycaemia. The diagnosis is suspected from the history of episodes of altered consciousness confirmed by demonstrating raised plasma insulin, C-peptide and proinsulin levels in peripheral blood in the presence of hypoglycaemia. Differentiation of the various causes of endogenous hyperinsulinism before surgery is difficult if not impossible and the low predictive value of most of the localizing techniques that are available makes them an additional and unnecessary cost, producing little clinical benefit. Hypoglycaemia caused by non-islet cell tumours (NICTH) is seemingly rarer than hyperinsulinism from insulinoma and tends to occur in older patients. The clinical features are similar to those of hyperinsulinism but laboratory investigation reveals appropriately depressed plasma insulin, C-peptide and proinsulin levels in the presence of hypoglycaemia. The plasma IGF-II:IGF-I ratio is characteristically high and the concentration of the E-domain of proIGF-II is raised. Autoimmune hypoglycaemia is more common in some countries than others and is most often due to autoantibodies to insulin (AIS). It may also be caused by autoantibodies to the insulin receptor and possibly to autoantibodies that are stimulatory to pancreatic beta-cells. Contrary to popular belief, idiopathic reactive hypoglycaemia is rare and only one of the possible causes of the postprandial syndrome. It is characterized by a low blood glucose concentration in blood collected during a spontaneous symptomatic episode but not at other times. Its cause is unknown. Other causes of hypoglycaemia include endocrinopathies of various kinds; sepsis including malaria; congestive cardiac failure; hepatic and renal insufficiencies; diverse inborn errors of metabolism; and exogenous toxins, of which alcohol is probably the commonest.

Polymorphism of insulin antibodies in six patients with insulin-immune hypoglycaemic syndrome

Insulin antibodies in six patients with immune hypoglycaemic syndrome were studied. The antibodies displayed a higher affinity for bovine insulin in two patients, were specific for human insulin in one patient and non-species specific in the other three patients. The predominant IgG subclass of the insulin antibodies was IgG4 in two patients, IgG3 in two and IgG1 in two. In one of these, the other three subclasses were also detectable. Insulin autoantibodies of four patients were homogeneous with regard to light chains (kappa), and those of the other two contained both kappa and gamma light chains. Analysis of insulin immune complex size by fast protein liquid chromatography was possible in three patients and demonstrated immune complexes with elution profile close to that of IgG, although not exactly superimposable to the one obtained with a mouse monoclonal insulin antibody. In two patients, avidity was too low to permit chromatography of the immune complexes, and, moreover, in these two cases insulin antibodies were of the IgG3 isotype and spontaneously formed aggregates independently of insulin binding. We conclude that insulin antibodies of the insulin immune syndrome are polymorphic but different from those generated by insulin therapy.

Autonomic nerve antibodies and autonomic nerve function in type 1 and type 2 diabetic patients

Complement-fixing adrenal medulla (CF-ADM), sympathetic ganglion (CF-SG), and vagal (CF-V) nerve antibodies were determined in diabetic patients. Among 74 patients with Type 1 diabetes, CF-ADM was detected in 7 (10%) cases, CF-SG in 14 (19%) cases, and CF-V in 8 (11%) cases. Among 38 patients with Type 2 diabetes, CF-ADM was detected in 5 (13%) cases, CF-SG in 4 (11%) cases, and CF-V in 6 (16%) cases. There were associations between autonomic nerve antibodies and autonomic nerve function. CF-ADM and/or CF-SG were significantly (P less than 0.002) less prevalent in Type 1 diabetic patients with autonomic neuropathy than in those without [5/44 (11%) vs. 14/30 (47%)] and, in agreement with this, the brake index, a sign of parasympathetic and sympathetic autonomic nerve function, was significantly (P less than 0.005) higher (more normal) in these patients (-0.56 +/- 0.13 vs. -1.04 +/- 0.12). In Type 2 diabetic patients, the E/I ratio, an index of parasympathetic nerve function, was significantly (P less than 0.03) lower (more abnormal) in those with CF-V than in those without (-1.81 +/- 0.17 vs. -1.20 +/- 0.11). In conclusion, the frequency of sympathetic nerve antibodies was decreased in Type 1 diabetic patients with autonomic neuropathy, while in Type 2 diabetic patients parasympathetic nerve antibodies were related to severe parasympathetic neuropathy.

Receptor autoimmunity in endocrine disorders

The discovery in 1956 of the long-acting thyroid stimulator of Graves' disease, now known as thyroid-stimulating antibodies, was seminal. A new mechanism for disease was revealed that appears applicable to virtually all endocrine systems, involving the growth as well as the function of endocrine cells. An endocrine gland may fail through at least three autoimmune mechanisms: destruction, atrophy, and inhibition of function. Destruction is probably irreversible but is not usually distinguishable clinically from receptor blockade causing atrophy or from metabolic unresponsiveness. The contribution made by receptor autoimmunity to endocrine diseases other than thyroid disease is at present unclear, but with immunologic manipulation it is potentially reversible, improving the replicative capacity of the gland, its metabolic responsiveness, or both.

Sexual precocity induced by ovarian follicular cysts. Is autoimmunity involved?

A 2-year-old girl presented with gonadotrophin-independent precocious puberty due to ovarian follicles. Central precocious puberty was excluded by several GnRH-tests and overnight LH sampling. There were no signs of McCune-Albright syndrome. An ovarian tumour was excluded by laparotomy and biopsies. Abdominal sonography demonstrated follicles occurring mostly in the left, sometimes in the right, ovary. Immunoglobulin G (IgG) purified from the patient's serum was capable of stimulating DNA synthesis in granulosa cells of rat ovarian segments kept in organ culture. Since FSH had a similar in-vitro action it is hypothesized that this patient's IgG mimics the action of FSH.

Antibody markers for type 1 diabetes: the issues

The detection of islet-cell-specific autoantibodies before clinical onset may mean that diabetes mellitus can be predicted, with important implications for targeting those to whom preventive treatment might be given. A large number of such markers have been proposed, but only high-titer islet cell antibodies have so far demonstrated the specificity and sensitivity to be of potential clinical value.