The clinical variability of maternally inherited diabetes and deafness is associated with the degree of heteroplasmy in blood leukocytes

CONTEXT

Maternally inherited diabetes and deafness (MIDD) is a rare form of diabetes with a matrilineal transmission, sensorineural hearing loss, and macular pattern dystrophy due to an A to G transition at position 3243 of mitochondrial DNA (mtDNA) (m.3243A>G). The phenotypic heterogeneity of MIDD may be the consequence of different levels of mutated mtDNA among mitochondria in a given tissue.

OBJECTIVE

The aim of the present study was thus to ascertain the correlation between the severity of the phenotype in patients with MIDD and the level of heteroplasmy in the blood leukocytes.

PARTICIPANTS

The GEDIAM prospective multicenter register was initiated in 1995. Eighty-nine Europid patients from this register, with MIDD and the mtDNA 3243A>G mutation, were included. Patients with MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) or with mitochondrial diabetes related to other mutations or to deletions of mtDNA were excluded.

RESULTS

A significant negative correlation was found between levels of heteroplasmy and age of the patients at the time of sampling for molecular analysis, age at the diagnosis of diabetes, and body mass index. After adjustment for age at sampling for molecular study and gender, the correlation between heteroplasmy levels and age at the diagnosis of diabetes was no more significant. The two other correlations remained significant. A significant positive correlation between levels of heteroplasmy and HbA(1c) was also found and remained significant after adjustment for age at molecular sampling and gender.

CONCLUSIONS

These results support the hypothesis that heteroplasmy levels are at least one of the determinants of the severity of the phenotype in MIDD.

131I-6 beta-iodomethylnorcholesterol scintigraphy: an assessment of its role in the investigation of adrenocortical incidentalomas

OBJECTIVE

Most incidentally discovered adrenal tumours ('incidentaloma') are benign adrenocortical adenomas. It has been suggested that 131I-6 beta-iodomethylnorcholesterol (IMC) scan could specify the degree of functional autonomy of such adenomas depending on whether they prevent contralateral adrenal tracer uptake. Our purpose was to examine this hypothesis in a correlated scintigraphic and endocrine study.

DESIGN

Prospective study evaluating the prevalence of unilateral IMC uptake (tumour uptake with no visualization of the contralateral adrenal gland) and bilateral uptake (uptake in both the tumoral and the contralateral adrenal glands) in patients with unilateral incidentaloma. Comparison of adrenocortical function and of IMC scan after dexamethasone (DXM) in the two scintigraphic groups thus defined.

PATIENTS

Thirty-five patients with a unilateral mass highly suggestive of benign adrenocortical adenoma on CT scan.

MEASUREMENTS

The IMC scan was performed in basal conditions (baseline scan) and after DXM (suppression scan). Adrenocortical function assessment included basal measurements of 11-deoxycortisol, 17 alpha-hydroxyprogesterone (17-OHP), dehydroepiandrosterone sulphate (DHEAS), plasma cortisol and ACTH, urinary free cortisol (UFC), overnight and low-dose DXM suppression test, and CRH test.

RESULTS

The baseline scan showed 16 patients (46%) with unilateral uptake (group A) and 19 (54%) with bilateral uptake (group B). Patients in group A exhibited lower ACTH values at 0800h (P = 0.05) and higher cortisol values after an overnight DXM suppression test (P = 0.02), than did patients in group B. In addition, 3 patients in group A failed the overnight and the low-dose DXM suppression tests. Adrenal masses were larger in group A than group B (P = 0.04) and an inverse correlation was found in the whole population between tumour size and ACTH value at 0800h (P = 0.05). On the suppression scan performed in 14 patients (7 in each group), patients in group A continued to exhibit unilateral tumour uptake and bilateral uptake was suppressed in 72% of patients in group B. An adrenal mass was removed in 3 patients of group A with confirmed benign adrenocortical adenomas. In the post-surgical period, the contralateral gland was again visualized in a baseline scan and the hormonal evaluation returned to the normal range.

CONCLUSION

Unilateral 131I-6 beta-iodomethylnorcholesterol tumour uptake is a frequent feature in benign adrenocortical adenomas. Hormonal data and scintigraphic profiles obtained after dexamethasone, as well as hormonoscintigraphic changes observed after surgery, provide evidence that unilateral uptake is related to functioning adenomas with various degrees of autononomy and suggest that the 131I-6 beta-iodomethylnorcholesterol scan could be a valuable tool for screening 'subclinical' Cushing's adenomas.

Vasopressin secretion during hyperglycemia in insulin-dependent diabetics

Plasma levels of vasopressin (AVP) were measured in ten insulin-dependent diabetic patients before and during intravenous administration of hypertonic glucose. Plasma glucose and plasma osmolality increased from 12.4 +/- 1.2 to 47.0 +/- 2.3 mmol/l and from 293 +/- 2.0 to 307 +/- 2.8 mosm/kg respectively. Plasma vasopressin increased in parallel from 5.6 +/- 0.6 to 7.7 +/- 0.6 pg/ml. The present results demonstrate that hyperglycemia may be an effective stimulus for AVP secretion in insulin-deficient diabetics.