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.

Congenital thyroid disease revisited: migrational anomalies and dyshormonogenesis

Nuclear medicine scintigraphy, in conjunction with other diagnostic tools, plays a vital role in assessing patients with congenital migrational anomalies. We present 5 patients, 4 of whom were hypothyroid and 1 patient who was euthyroid. Scintigraphic and ultrasonographic images were examined and correlated with laboratory results. These patients demonstrate the spectrum of migrational anomalies of the thyroid. Nuclear medicine scintigraphy was a valuable aid in establishing the location of the ectopic thyroid as well as its function.

Increased serum 1,25-dihydroxyvitamin D after growth hormone administration is not parathyroid hormone-mediated

To assess the effects of growth hormone (GH) on serum 1,25-dihydroxyvitamin D [1,25(OH)2D], we performed the following prospective crossover study in six healthy, young, adult, white men. During each of two admissions for 2 1/2 days to a general clinical research center, subjects were placed on a daily dietary calcium intake of 400 mg. Serum calcium, phosphorus, 1,25(OH)2D, immunoreactive intact parathyroid hormone (PTH), insulin-like growth factor I (IGF-I), IGF binding protein 3 (IGFBP3), tubular reabsorption of phosphate (TMP/GFR) were measured. Recombinant human GH (rhGH, Humatrope) (25 microg/kg/day subcutaneously for 1 week) was administered prior to and during one of the admissions. Results are expressed as mean +/- SEM. Whereas serum 1,25(OH)2D (58.9 +/- 7.7 versus 51.6 +/- 7.4 pg/ml, P< 0.01), serum phosphorus (4.5 +/- 0.1 versus 3.7 +/- 0.1 mg/dl, P < 0.01), TRP (92.0 +/- 0.5 versus 87.8 +/- 0.7 mg/dl, P < 0.005), TMP/GFR (4.6 +/- 0.1 versus 3.5 +/- 0.2, P < 0.005), and urinary calcium (602 +/- 49 versus 346 +/- 25 mg/day, P < 0.001) increased significantly, serum PTH decreased significantly (19.9 +/- 1.9 versus 26.8 +/- 4.0 pg/ml, P < 0.05) and serum calcium did not change when subjects received rhGH. These findings indicate that in humans, GH affects serum 1,25(oh)2D independently of circulating PTH and that this effect is mediated by IGF-I. We propose, therefore, that one potential mechanism by which GH stimulates increases in bone mass is via modest increases in serum 1,25(OH)2D.

Demonstration of a lack of racial difference in secretion of growth hormone despite a racial difference in bone mineral density in premenopausal women--a Clinical Research Center study

We previously found GH secretion to be higher in black than white men. Therefore, we performed studies to determine whether this racial difference in GH secretion also occurs in women. Measurements of GH were obtained at 20-min intervals over 24 h and analyzed by deconvolution in 12 healthy black and 12 healthy white premenopausal women. Bone mineral density (BMD) was determined by dual energy x-ray absorptiometry, and GM allotypes were measured as a genetic marker for race. Racial distribution of the groups, as determined by analysis of GM haplotypes, were typical for black and white American populations. Twenty-four-hour integrated GH concentration, GH secretory burst amplitude, burst frequency, half-duration, mass, and half-life were not different in the two groups. Serum testosterone was modestly, but significantly, greater in the black than in the white women (1.1 +/- 0.1 vs. 0.9 +/- 0.1 nmol/L; P < 0.05). Serum 17 beta-estradiol and insulin-like growth factor (IGF)-binding protein-3 were not different in the two groups. However, the IGF-I/IGF-binding protein-3 molar ratio was significantly greater in the black than the white women (2.0 +/- 0.1 vs. 1.6 +/- 0.1; P < 0.02). The BMD of total body (1.12 +/- 0.02 vs. 1.07 +/- 0.02 g/cm2; P < 0.05) and total hip (0.96 +/- 0.04 vs. 0.86 +/- 0.04 g/cm2, P < 0.05) were greater in the black (n = 13) than in the white (n = 12) women. There was a trend toward greater BMD of the forearm in the black women (0.58 +/- 0.01 vs. 0.56 +/- 0.01 g/cm2; P = 0.06) and no racial difference in the BMD of the spine. When examining all subjects together, the BMD of the total body, trochanter, and spine correlated with total integrated GH secretion. Thus, the racial difference in GH secretion that we had previously found in men does not occur in women despite the higher BMD values at several skeletal sites in black women.

Greater secretion of growth hormone in black than in white men: possible factor in greater bone mineral density--a clinical research center study

To determine why blacks have a higher bone mineral density (BMD) and lower incidence of osteoporosis and fractures than whites, we investigated whether the secretion of GH is higher in black than in white men. Measurements of GH were obtained at 20-min intervals over 24 h and analyzed by deconvolution. BMD was determined by dual energy x-ray absorptiometry in 16 normal black and 17 normal white men, aged 20-40 yr. The 24-h integrated GH concentration 942 +/- 174 vs. 602 +/- 104 micrograms/L; P = 0.0495) and GH secretory burst amplitude (0.499 +/- 0.163 vs. 0.169 +/- 0.027 micrograms/L.min; P = 0.0482) were higher in black than in white men. GH burst frequency, half-duration, mass, and half-life were not different in the 2 groups. The serum 17 beta-estradiol level (162 +/- 12 vs. 108 +/- 11 pmol/L; P = 0.0011) was higher, and the serum insulin-like growth factor-binding protein 3 level (2.2 +/- 0.1 vs. 2.8 +/- 0.1 microgram/mL; P = 0.0001) was lower in black than in white men. BMD values for total body (1.22 +/- 0.02 vs. 1.14 +/- 0.02 g/cm2; P = 0.0041), forearm (0.69 +/- 0.01 vs. 0.66 +/- 0.01 g/cm2; P = 0.0211), trochanter (0.91 +/- 0.03 vs. 0.77 +/- 0.03 g/cm2; P = 0.0003), and femoral neck (1.08 +/- 0.03 vs. 0.93 +/- 0.03 g/cm2; P = 0.0007) were higher in black than in white men. Thus, serum 17 beta-estradiol level, GH secretion, and BMD values for the total body, forearm, trochanter, and femoral neck are greater in black than in white men. As estrogen is known to increase GH secretion and GH to increase bone mass, increases in circulating 17 beta-estradiol may contribute to the higher GH secretion and bone mass in black men.

Long-chain acyl-CoA profiles in cultured fibroblasts from patients with defects in fatty acid oxidation

Negative chemical ionization (NCI) mass spectrometry was used to quantify the acyl-CoA intermediates present in human fibroblasts growing in media containing the long-chain fatty acid, palmitate. The acyl-CoA intermediates were detected as the N-acyl pentafluorobenzyl glycinates. In fibroblasts from normal individuals only saturated acyl-CoA esters were detected, supporting the concept that the acyl-CoA dehydrogenase reaction is the rate-limiting step of intramitochondrial fatty acid oxidation. In patients with inherited enzymatic defects of intramitochondrial long-chain fatty acid oxidation, there was not a significant increase in the amount of long-chain acyl-CoA compounds, with palmitoyl-CoA amounts similar to those found in controls. However, there was a sharp decrease in the relative amount of lauroyl-CoA and a resultant sixfold elevation in the palmitoyl-CoA:lauroyl-CoA ratio. In contrast, fibroblasts with a defect involving the transport of fatty acids across the mitochondrial membrane, carnitine palmitoyl transferase 1 deficiency, had a fourfold increase in palmitoyl-CoA. Our results suggest that acyl-CoA esters in biological tissues are readily detectable using NCI mass spectrometry. This approach is significantly more sensitive than previous methods for the detection of these important metabolic intermediates, and may prove useful in the study of fatty acid oxidation in both normal and enzyme-deficient tissues.