Identical and Nonidentical Twins: Risk and Factors Involved in Development of Islet Autoimmunity and Type 1 Diabetes

OBJECTIVE

There are variable reports of risk of concordance for progression to islet autoantibodies and type 1 diabetes in identical twins after one twin is diagnosed. We examined development of positive autoantibodies and type 1 diabetes and the effects of genetic factors and common environment on autoantibody positivity in identical twins, nonidentical twins, and full siblings.

RESEARCH DESIGN AND METHODS

Subjects from the TrialNet Pathway to Prevention Study (N = 48,026) were screened from 2004 to 2015 for islet autoantibodies (GAD antibody [GADA], insulinoma-associated antigen 2 [IA-2A], and autoantibodies against insulin [IAA]). Of these subjects, 17,226 (157 identical twins, 283 nonidentical twins, and 16,786 full siblings) were followed for autoantibody positivity or type 1 diabetes for a median of 2.1 years.

RESULTS

At screening, identical twins were more likely to have positive GADA, IA-2A, and IAA than nonidentical twins or full siblings (all P < 0.0001). Younger age, male sex, and genetic factors were significant factors for expression of IA-2A, IAA, one or more positive autoantibodies, and two or more positive autoantibodies (all P ≤ 0.03). Initially autoantibody-positive identical twins had a 69% risk of diabetes by 3 years compared with 1.5% for initially autoantibody-negative identical twins. In nonidentical twins, type 1 diabetes risk by 3 years was 72% for initially multiple autoantibody-positive, 13% for single autoantibody-positive, and 0% for initially autoantibody-negative nonidentical twins. Full siblings had a 3-year type 1 diabetes risk of 47% for multiple autoantibody-positive, 12% for single autoantibody-positive, and 0.5% for initially autoantibody-negative subjects.

CONCLUSIONS

Risk of type 1 diabetes at 3 years is high for initially multiple and single autoantibody-positive identical twins and multiple autoantibody-positive nonidentical twins. Genetic predisposition, age, and male sex are significant risk factors for development of positive autoantibodies in twins.

Radiation Safety Aspects of Iodine-131 metaiodobenzylguanidine (131I mIBG) Therapy Program Startup

As a medical center without a pre-existing radiopharmaceutical therapy program, it was a daunting endeavor to implement a I metaiodobenzylguanidine (mIBG) high-dose treatment regimen. It took several years of planning with hospital administration, vendors, and Texas Department of Health Radiological Control regulators to establish a viable program. Effective communication between physicians, nursing, nuclear medicine, environmental services, maintenance, and other support staff is essential and paramount for the successful execution and continued sustainability of the mIBG therapy program. Besides providing an effective treatment for patients, an additional goal for the program is to keep radiation exposure As Low As Reasonably Achievable (ALARA) for staff and patient caregivers. As such, start-up presented many training, logistical, and radiation safety challenges. The location of the isolation room and shielding specifications were designed to keep radiation exposure to public access areas to less than 2 microsieverts per hour. Before the first patient was treated the policies and procedures for training, radiation safety, product quality control, and infusion process needed to be developed, tested, and approved by various committees. Furthermore, a similar process was required for developing room set-up, post therapy cleanup, and waste storage procedures. Throughout the maturation process of the program, the departments involved have found that our safety culture has continually improved by the re-enforcement of knowledge and lessons learned, as both the ancillary and treatment staff grew more confident in each other's ability during more patient treatments are performed. This article describes the process and lessons learned during the time leading up to the startup and early years of the mIBG therapy program.

Low-Dose Anti-Thymocyte Globulin (ATG) Preserves β-Cell Function and Improves HbA1c in New-Onset Type 1 Diabetes

OBJECTIVE

A pilot study suggested that combination therapy with low-dose anti-thymocyte globulin (ATG) and pegylated granulocyte colony-stimulating factor (GCSF) preserves C-peptide in established type 1 diabetes (T1D) (duration 4 months to 2 years). We hypothesized that 1) low-dose ATG/GCSF or 2) low-dose ATG alone would slow the decline of β-cell function in patients with new-onset T1D (duration <100 days).

RESEARCH DESIGN AND METHODS

A three-arm, randomized, double-masked, placebo-controlled trial was performed by the Type 1 Diabetes TrialNet Study Group in 89 subjects: 29 subjects randomized to ATG (2.5 mg/kg intravenously) followed by pegylated GCSF (6 mg subcutaneously every 2 weeks for 6 doses), 29 to ATG alone (2.5 mg/kg), and 31 to placebo. The primary end point was mean area under the curve (AUC) C-peptide during a 2-h mixed-meal tolerance test 1 year after initiation of therapy. Significance was defined as one-sided P value < 0.025.

RESULTS

The 1-year mean AUC C-peptide was significantly higher in subjects treated with ATG (0.646 nmol/L) versus placebo (0.406 nmol/L) (P = 0.0003) but not in those treated with ATG/GCSF (0.528 nmol/L) versus placebo (P = 0.031). HbA_1c was significantly reduced at 1 year in subjects treated with ATG and ATG/GCSF, P = 0.002 and 0.011, respectively.

CONCLUSIONS

Low-dose ATG slowed decline of C-peptide and reduced HbA_1c in new-onset T1D. Addition of GCSF did not enhance C-peptide preservation afforded by low-dose ATG. Future studies should be considered to determine whether low-dose ATG alone or in combination with other agents may prevent or delay the onset of the disease.

A Type 1 Diabetes Genetic Risk Score Predicts Progression of Islet Autoimmunity and Development of Type 1 Diabetes in Individuals at Risk

OBJECTIVE

We tested the ability of a type 1 diabetes (T1D) genetic risk score (GRS) to predict progression of islet autoimmunity and T1D in at-risk individuals.

RESEARCH DESIGN AND METHODS

We studied the 1,244 TrialNet Pathway to Prevention study participants (T1D patients' relatives without diabetes and with one or more positive autoantibodies) who were genotyped with Illumina ImmunoChip (median [range] age at initial autoantibody determination 11.1 years [1.2-51.8], 48% male, 80.5% non-Hispanic white, median follow-up 5.4 years). Of 291 participants with a single positive autoantibody at screening, 157 converted to multiple autoantibody positivity and 55 developed diabetes. Of 953 participants with multiple positive autoantibodies at screening, 419 developed diabetes. We calculated the T1D GRS from 30 T1D-associated single nucleotide polymorphisms. We used multivariable Cox regression models, time-dependent receiver operating characteristic curves, and area under the curve (AUC) measures to evaluate prognostic utility of T1D GRS, age, sex, Diabetes Prevention Trial-Type 1 (DPT-1) Risk Score, positive autoantibody number or type, HLA DR3/DR4-DQ8 status, and race/ethnicity. We used recursive partitioning analyses to identify cut points in continuous variables.

RESULTS

Higher T1D GRS significantly increased the rate of progression to T1D adjusting for DPT-1 Risk Score, age, number of positive autoantibodies, sex, and ethnicity (hazard ratio [HR] 1.29 for a 0.05 increase, 95% CI 1.06-1.6; P = 0.011). Progression to T1D was best predicted by a combined model with GRS, number of positive autoantibodies, DPT-1 Risk Score, and age (7-year time-integrated AUC = 0.79, 5-year AUC = 0.73). Higher GRS was significantly associated with increased progression rate from single to multiple positive autoantibodies after adjusting for age, autoantibody type, ethnicity, and sex (HR 2.27 for GRS >0.295, 95% CI 1.47-3.51; P = 0.0002).

CONCLUSIONS

The T1D GRS independently predicts progression to T1D and improves prediction along T1D stages in autoantibody-positive relatives.

Effect of gastro-intestinal conditions on the growth of Enterococcus mundtii ST4SA, and production of bacteriocin ST4SA recorded by real-time PCR

Enterococcus mundtii ST4SA, isolated from soybeans, produces a 3950 Da bacteriocin (bacST4SA) active against a variety of Gram-positive and Gram-negative bacteria, including human pathogens. In this study, the effect of gastro-intestinal conditions on the survival of strain ST4SA and production of bacST4SA was studied. Strain ST4SA was cultured in MRS broth at different pH and in MRS broth supplemented with bile, pancreatic enzymes, and contents of the stomach and small intestine of pigs, respectively. After 12 and 24 h at 37 degrees C, cells were harvested, RNA isolated and cDNA prepared. Expression of the genes encoding bacST4SA, RecA, GroES and 23 S rRNA was studied by real-time PCR (RT-PCR). No significant up- or down-regulation of the genes were recorded, except when cells were grown in MRS at pH 3.5. In this case only RecA and GroES were up-regulated. Growth of strain ST4SA and production of bacST4SA are not affected by conditions in the lower intestine and the strain could be used as a probiotic.

[Inhibition of the 3' to 5' exonuclease activity of the DNA polymerase I of Escherichia coli by deoxyribonucleotides]

The 3' à 5' exonuclease activity of E. coli DNA-polymerase I is inhibited by nucleotides and deoxynucleotides at concentrations (< 1 mM) where polymerase activity is not affected. This inhibitory effect depends on the nature of the excised deoxynucleotide, excision of purines being much less inhibited than that of pyrimidines. It does not depend on the purine or pyrimidine nature of the inhibitor.

Urinary 3-methoxy-4-hydroxymandelic acid as measured by liquid chromatography, with on-line post-column reaction

We describe a method for measurement of 3-methoxy-4-hydroxymandelic acid (vanillylmandelic acid, VMA) in urine. After the pH of the urine is adjusted to 2.7 and the sample is filtered, exactly 15 microL is injected onto a C-18 reversed-phase column. VMA is eluted from the column with 10 mmol/L phosphate buffer, pH 2.7, containing 30 mL of acetonitrile per liter. The eluate stream is combined with alkaline periodate and then passed through a 60 degrees C water bath. The VMA is completely oxidized to vanillin, which is detected and quantitiated by its absorbance at 360 nm. No deterioration of the column was noted after 167 such injections of urine samples. Long-term control data indicate a CV of 12 and 10% at VMA concentrations of 1.5 and 5.8 mg/L, respectively. Although results correlate well (r = 0.976) with those by the method of Pisano et al. [Clin. Chim. Acta 7, 285 (1962)], they average 10% lower. Of 20 compounds tested, only methyl dopa interfered with the procedure as described.

Urinary 3-methoxy-4-hydroxymandelic acid as measured by liquid chromatography, with on-line post-column reaction

We describe a method for measurement of 3-methoxy-4-hydroxymandelic acid (vanillylmandelic acid, VMA) in urine. After the pH of the urine is adjusted to 2.7 and the sample is filtered, exactly 15 microL is injected onto a C-18 reversed-phase column. VMA is eluted from the column with 10 mmol/L phosphate buffer, pH 2.7, containing 30 mL of acetonitrile per liter. The eluate stream is combined with alkaline periodate and then passed through a 60 degrees C water bath. The VMA is completely oxidized to vanillin, which is detected and quantitiated by its absorbance at 360 nm. No deterioration of the column was noted after 167 such injections of urine samples. Long-term control data indicate a CV of 12 and 10% at VMA concentrations of 1.5 and 5.8 mg/L, respectively. Although results correlate well (r = 0.976) with those by the method of Pisano et al. [Clin. Chim. Acta 7, 285 (1962)], they average 10% lower. Of 20 compounds tested, only methyl dopa interfered with the procedure as described.

Des-Nalpha-acetyl-alpha-melanotropin: a synthetic substrate for specific N-terminal directed enzymatic acetylation

Application of the 2-methylsulfonylethyloxycarbonyl group for temporary amino protection enables the synthesis from one precursor of des-Nalpha1-acetyl-alpha-MSH, the two mono N-acetylated forms (in positions I and II) and the diacetyl form of this tridecapeptide amideq The free tridecapeptide amide, although structurally unrelated to the normal substrate, was recognized by an enzyme occurring in calf eye-lens tissue. The product of the enzymatic reaction was exclusively alpha-MSH. Partial sequences derived from the N-terminus were less rapidly acetylated or not at all, depending on their chain length. The enzyme, therefore, appears to direct its activity to free N-terminal alpha-amino groups of peptides exceeding a certain critical chain length. Acetylation of epsilon-amino functions did not occur.

Model studies of enzymatic NH2-terminal acetylation of porteins with des-Nalpha1-acetyl-alpha-melanotropin as a substrate

The present study describes the acetylation by an enzyme present in calf lens of a synthetic tridecapeptide [analogous to alpha-melanotropin (alpha-melanocyte stimulating hormone) but lacking the naturally occurring NH2-terminal acetyl group: des-Nalpha1-Ac-alpha-melanotropin]. The reaction is specific for the alpha-amino group of the NH2-terminal amino acid. The minimum length required for the substrate to become acetylated appears to be a sequence of five to eight amino acid residues. Modification of the internal lysine decreases the incorporation of acetate, irrespective of the size of the blocking group.