Werner A. Scherbaum

Glutamic acid decarboxylase (GAD) autoantibodies are additional predictive markers of Type 1 (insulin-dependent) diabetes mellitus in high risk individuals

SummaryThe prevalence of glutamic acid decarboxylase autoantibodies was determined with an immunotrapping enzyme activity assay in newly-diagnosed Type 1 (insulin-dependent) diabetic patients as well as in first-degree relatives using rat brain homogenate as a source of glutamate decarboxylase. Twenty-six out of 86 islet-cell cytoplasmic autoantibody positive and one out of 24 islet cell autoantibody negative patients of recent onset, had autoantibodies to glutamate decarboxylase above the upper 99% confidence limit obtained from 89 control sera. Among 27 islet cell autoantibody positive relatives including 19 siblings and 8 parents, antibodies to glutamate decarboxylase were found in 8 of 9 (89%) relatives and 7 of 8 (87.5%) siblings with islet cell autoantibody titres above 20 JDF units, in 1 of 19 (5.2%) relatives with islet cell autoantibody titres between 2 and 5 JDF units, in 2 of 263 (0.7%) siblings and 1 of 139 parents without islet cell autoantibodies. In first-degree relatives, high titre islet cell autoantibodies and autoantibodies to glutamate decarboxylase were tightly associated (X2=182, p=0.0001). None of the relatives with low genetic risk (n=64), i.e. HLA-different to the diabetic proband, was found to be antibody positive. Antibodies to glutamate decarboxylase were present only in those relatives sharing at least one haplotype with the diabetic proband, including two islet cell autoantibody negative but HLA-identical siblings. Autoantibodies to glutamate decarboxylase were present in 7 of 9 (77%) relatives who developed the disease, including one islet cell autoantibody negative sibling. Altogether, the simultaneous presence of autoantibodies to glutamate decarboxylase and high titre islet cell autoantibody increases the positive predictive value for the disease from 66% to 75%. This study indicates therefore that autoantibodies to glutamate decarboxylase detected by an immunotrapping enzyme activity assay are additional predictive markers for future development of Type 1 diabetes and should be now prospectively studied in high risk individuals as well as other autoantibodies to Beta-cell autoantigens.

Gonadotropin Secretion during Aging in Postmenopausal Women

Although chronological aging is known to result in reduced gonadotropin secretion in women, the precise mechanisms to account for this neuroendocrine manifestation are yet obscure. To evaluate the extent to which the pituitary and/or hypothalamus are involved in the process of aging, we aimed at characterizing the unstimulated and GnRH-stimulated gonadotropin secretion in postmenopausal women (PMW) of different ages. Accordingly, 9 younger PMW (mean age: 53.8 years) in their first and 9 older PMW (mean age: 80.3 years) in their 4th decade of life after natural onset of menopause were studied. In both groups, blood was collected at 10-min intervals for 10 h, while GnRH (25 micrograms i.v.) was administered 8 h after initiation of blood samplings. Compared to younger PMW, basal serum concentrations of dehydroepiandrosterone-sulfate were lower (p less than 0.05) in older PMW, while estrogen (estradiol, estrone), androgen (testosterone, androstendione) and sex hormone binding globulin levels were similar. Lower (p less than 0.01) mean LH levels composed of attenuated (p less than 0.05) LH pulse amplitudes and pulse frequencies (as determined by the cluster pulse algorithm) were found in the 8-hour LH secretory profiles of older PMW. Furthermore, the FSH secretion of older PMW was characterized by lower (p less than 0.01) mean FSH levels with lower (p less than 0.05) FSH pulse amplitudes, but not pulse frequencies. The absolute peak concentrations attained and the total amount of LH and FSH released in response to GnRH stimulations were blunted (p less than 0.001) in older PMW.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Protein for Human Growth Hormone: Effects of Age and Weight

In human serum, a specific binding protein with high affinity for human growth hormone (GHBP) is found which is identical to the extracellular portion of the hepatic GH receptor. GHBP is assessed by incubating serum samples with [125I]-GH, followed by separation of bound and free radioactivity using gel chromatography. In newborns and children younger than 2 months, GHBP was practically absent and no big-big GH could be found. GHBP values increased rapidly during the first 2 years of life, followed by a slower increase during childhood and puberty. No difference was found between male and female subjects. Apart from age, standardized weight (SDS = z score) had a major positive effect on GHBP concentration. Interestingly, SDS height correlated negatively with GHBP when weight and age were controlled for. These data may relate to two clinical findings: (1) the developmental switch between GH-independent intrauterine and GH-dependent postnatal growth mechanisms, and (2) the accelerated growth velocity encountered in adipose children.

Antibodies to the Mr 64,000 (64K) protein in islet cell antibody positive non-diabetic individuals indicate high risk for impaired Beta-cell function

SummaryA prospective study of a normal childhood population identified 44 islet cell antibody positive individuals. These subjects were typed for HLA DR and DQ alleles and investigated for the presence of antibodies to the Mr 64,000 (64K) islet cell antigen, complement-fixing islet cell antibodies and radiobinding insulin autoantibodies to determine their potency in detecting subjects with impaired Beta-cell function. At initial testing 64K antibodies were found in six of 44 islet cell antibody positive subjects (13.6%). The same sera were also positive for complement-fixing islet cell antibodies and five of them had insulin autoantibodies. During the follow-up at 18 months, islet cell antibodies remained detectable in 50% of the subjects studied. In all six cases who were originally positive, 64K antibodies were persistently detectable, whereas complement-fixing islet cell antibodies became negative in two of six and insulin autoantibodies in one of five individuals. HLA DR4 (p < 0.005) and absence of asparic acid (Asp) at position 57 of the HLA DQ β chain (p < 0.05) were significantly increased in subjects with 64K antibodies compared with control subjects. Of 40 individuals tested in the intravenous glucose tolerance test, three had a first phase insulin response below the first percentile of normal control subjects. Two children developed Type 1 (insulin-dependent) diabetes mellitus after 18 and 26 months, respectively. Each of these subjects was non-Asp homozygous and had persistent islet cell and 64K antibodies. We conclude that 64K antibodies, complement-fixing islet cell antibodies and insulin autoantibodies represent sensitive serological markers in assessing high risk for a progression to Type 1 diabetes in islet cell antibody positive non-diabetic individuals.

Prevalence of autoantibodies to endocrine organs in girls with Ullrich-Turner syndrome aged 5-14 years.

Endocrine function tests and a broad panel of autoantibodies to endocrine organs were assessed in 77 patients aged 5-14 years with Ullrich-Turner syndrome (UTS), who were included in the German UTS Multicenter Study. None of these patients had abnormal pituitary, thyroid or adrenocortical function, as assessed by the adequate hormone tests. Antibodies to thyroid microsomes were found in 3 of the 77 (3.9%), antibodies to thyroglobulin in 0/77, antibodies to adrenocortical cells in 1/77 (1.3%), gastric parietal cell antibodies in 2/77 (2.6%), and anterior pituitary cell antibodies in 3/77 (3.9%) probands. These prevalences were not significantly higher than those obtained in 154 age- and sex-matched normal control children when 2 control subjects were assigned to each patient with UTS. Our data do not show an increase in serological signs of endocrine autoimmunity in young patients with UTS suggesting that a putative association of these syndromes does not exist from birth and is not usually present in childhood. However, we cannot exclude the possibility that UTS is associated with factors that render these patients more susceptible to endocrine autoimmunity later in life.

Human monoclonal islet specific autoantibodies share features of islet cell and 64 kDa antibodies

SummaryThe first human monoclonal islet cell antibodies of the IgG class (MICA 1-6) obtained from an individual with Type 1 (insulin-dependent) diabetes mellitus were cytoplasmic islet cell antibodies selected by the indirect immunofluorescence test on pancreas sections. Surprisingly, they all recognized the 64 kDa autoantigen glutamate decarboxylase. In this study we investigated which typical features of cytoplasmic islet cell antibodies are represented by these monoclonals. We show by double immunofluorescence testing that MICA 1-6 stain pancreatic beta cells which is in agreement with the beta-cell specific expression of glutamate decarboxylase. In contrast an islet-reactive IgM monoclonal antibody obtained from a pre-diabetic individual stained all islet cells but lacked the tissue specificity of MICA 1-6 and must therefore be considered as a polyreactive IgM-antibody. We further demonstrate that MICA 1-6 revealed typical features of epitope sensitivity to biochemical treatment of the target tissue which has been demonstrated for islet cell antibodies, and which has been used to argue for a lipid rather than a protein nature of target antigens. Our results provide direct evidence that the epitopes recognized by the MICA are destroyed by methanol/chloroform treatment but reveal a high stability to Pronase digestion compared to proinsulin epitopes. Conformational protein epitopes in glutamate decarboxylase therefore show a sensitivity to biochemical treatment of sections such as ganglioside epitopes. MICA 1-6 share typical features of islet cell and 64 kDa antibodies and reveal that glutamate decarboxylase-reactive islet cell antibodies represent a subgroup of islet cell antibodies present in islet cell antibody-positive sera.

No association between islet cell antibodies and coxsackie B, mumps, rubella and cytomegalovirus antibodies in non-diabetic individuals aged 7–19 years

SummaryViral antibodies were tested in a cohort of 44 isletcell antibody-positive individuals age 7–19 years, and 44 of their islet cell antibody-negative age and sex-matched classmates selected from a population study of 4208 pupils who had been screened for islet cell antibodies. Anti-coxsackie B1-5 IgM responses were detected in 14 of 44 (32%) of the islet cell antibody-positive subjects and in 7 of 44 (16%) control subjects. This difference did not reach the level of statistical significance. None of the islet cell antibody-positive subjects had specific IgM antibodies to mumps, rubella, or cytomegalovirus. There was also no increase in the prevalence or the mean titres of anti-mumps-IgG or IgA and anti-cytomegalovirus-IgG in islet cell antibody-positive subjects compared to control subjects. These results do not suggest any association between islet cell antibodies, and possibly insulitis, with recent mumps, rubella or cytomegalo virus infection. Further studies are required to clarify the relationship between islet cell antibodies and coxsackie B virus infections.