Glutamic acid decarboxylase (GAD; glutamate decarboxylase, L-glutamate 1-carboxy-lyase, EC 4.1.1.15), which catalyzes formation of gamma-aminobutyric acid from L-glutamic acid, is detectable in different isoforms with distinct electrophoretic and kinetic characteristics. GAD has also been implicated as an autoantigen in the vastly differing autoimmune disease stiff-man syndrome and insulin-dependent diabetes mellitus. Despite the differing GAD isoforms, only one type of GAD cDNA (GAD-1), localized to a syntenic region of chromosome 2, has been isolated from rat, mouse, and cat. Using sequence information from GAD-1 to screen a human pancreatic islet cDNA library, we describe the isolation of an additional GAD cDNA (GAD-2), which was mapped to the short arm of human chromosome 10. Genomic Southern blotting with GAD-2 demonstrated a hybridization pattern different from that detected by GAD-1. GAD-2 recognizes a 5.6-kilobase transcript in both islets and brain, in contrast to GAD-1, which detects a 3.7-kilobase transcript in brain only. The deduced 585-amino acid sequence coded for by GAD-2 shows less than 65% identity to previously published, highly conserved GAD-1 brain sequences, which show greater than 96% deduced amino acid sequence homology among the three species. The function of this additional islet GAD isoform and its importance as an autoantigen in insulin-dependent diabetes remain to be determined.

These data suggest a high variability between centres regarding the prevalence of emerging bacteria. Most patients maintained a stable clinical condition during the 6-month study period despite being colonised with emerging bacteria.

Summary. First-degree relatives of Type i (insulin-dependent) diabetic patients are at increased risk for developing clinical diabetes. The presence of islet cell or insulin autoantibodies further identifies relatives at greater risk, but not all immunologic-marker-positive relatives progress to disease. Beta-cell dysfunction, however, seems to be more prevalent than clinical Type 1 diabetes, since stable subclinical pancreatic Beta-cell dysfunction may occur. Antibodies against a Mr 64,000 (64K) islet Beta-cell protein, identified as glutamic acid decarboxylase, have been reported both at and several years prior to the clinical onset of Type i diabetes. We measured 64K antibodies in first-degree relatives with varying degrees of Beta-cell dysfunction and risk for subsequent Type i diabetes to determine whether 64K antibodies improve the predictive power of islet cell antibodies and/or insulin autoantibodies. In the Seattle Family Study first-degree relatives of Type 1 diabetic patients are followed prospectively using detailed Beta-cell function tests, insulin sensitivity, quantitative evaluation of islet cell antibodies and fluid phase assay insulin autoantibodies. 64K antibodies were measured using dog islets. Relatives were selected, based on Beta-cell function to represent individuals at high (n = 6) and low (n = 30) risk for subsequent Type 1 diabetes. The 30 low-risk individuals followed-up for 78 months, had stable Beta-cell function, and six (20%) were negative for all autoantibodies, ten (33%) were positive for insulin autoantibodies, 16 (53%) were islet cell antibody positive While six (20%) were positive for 64K antibodies. In contrast, of the six subjects with progressively declining Beta-cell function who are therefore at high risk, two of whom have already developed Type i diabetes, two (33%) were positive for insulin autoantibodies, four (67%) were islet cell antibody positive, while all six (100%) were positive for 64K antibodies. We conclude that antibodies to the Mr 64,000 islet protein correlate with progressive Beta-cell dysfunction more closely than either islet cell antibodies or insulin autoantibodies, but can sometimes be present in individuals whose Beta-cell function remains stable over several years.

The prevalence of cystic fibrosis-related diabetes melltitus (CFRD) is increasing as patients with cystic fibrosis (CF) live longer. Because patients with CFRD are insulin-deficient, the standard medical treatment is exogenous insulin. Sulfonylureas enhance insulin secretion by acting on a specific islet beta cell receptor. No data are available about the outcome of sulfonylurea treatment vs. insulin treatment. In this retrospective study, data from 45 patients with CFRD were analyzed regarding their clinical outcome as it related to the treatment protocol. The duration of DM treatment was 7.6 +/- 4.6 years in the insulin-treated group and 3.5 +/- 2.0 years in the sulfonylurea group (n.s.). The age of CFRD diagnosis was significantly earlier in patients treated with insulin (n = 34) than in the patients treated with sulfonylurea (n = 11) (16.4 +/- 3.6 vs. 24.2 +/- 4.8 years, P < 0.001). No statistical differences were found between the two groups in the time of CF diagnosis, the most recent forced expired volume in 1 sec, forced vital capacity, Shwachman score, hemoglobin A(1C) levels, or weight for height index at the end of the study. Our data suggest that a subgroup of CFRD patients can be managed for a number of years with sulfonylurea, and that the clinical outcome was not different in this group compared with the insulin-treated patients.

Quantification of islet cell antibodies is used increasingly to evaluate pre-clinical Type 1 (insulin-dependent) diabetes mellitus. If expression of the antigen(s) reacting with islet cell antibodies varies depending upon the functional state of the pancreatic islets, this may partly explain differences in assay sensitivity between laboratories. To address this question we altered Beta-cell function in Osborn-Mendel rats, by dietary manipulation prior to killing. Rats were fed chow (n = 7) or a high sucrose/high fat "cafeteria" diet (n = 8) or were fasted for 18 h (n = 6) until immediately prior to killing. Using frozen sections of these rat pancreata in the indirect immunofluorescent test for islet cell antibodies, we determined the end-point titre for 18 sera in which islet cell antibodies had been previously quantified in our standard human pancreas assay. These sera included ten positive sera and eight normal negative control sera. The four most strongly positive sera gave significantly higher end-point titres on "cafeteria" diet-fed pancreata and lower titres on fasted pancreata (p less than 0.04 to 0.002). None of non-diabetic control sera were positive on any substrate. These data suggest that islet antigen expression is increased when Beta-cell function is increased by dietary manipulation. Improved sensitivity in the islet cell antibody assay might be possible by altering Beta-cell function before or immediately after pancreas collection.