News for the practitioner

News for the practitioner     

Non-enzymatic glycosylation. Biology. Pathology

Enzymatic glycosylation of proteins should be clearly distinguished from non-enzymatic glycosylation or glycation. Both processes occur in normal subjects but are enhanced in patients with hyperglycemia. Increased enzymatic glycation in patients with diabetes mellitus is responsible for thickening and weakening of capillary membranes, resulting in microangiopathy with microaneurisms, bleeding, and circulatory exclusion. Non-enzymatic glycosylation (glycation) affects all the proteins in the body and, if intense enough, may modify the activity or effectiveness of some molecules (apolipoproteins, membrane receptors, or even insulin itself). In everyday practice, glycated serum albumin and, above all, glycated hemoglobin serve as markers to evaluate the effectiveness of therapy in patients with diabetes mellitus.     

HLA haplotype study of 53 juvenile insulin-dependent diabetic (I.D.D.) families

Fifty-three families with at least one IDD patient were genotyped for 5 markers of the HLA complex including Bf and DR. In 8 families one of the parents was also affected and in 12 families more than two children were diseased. In total, 76 patients were genotyped. Their haplotypes were compared with those of 106 unrelated controls (the parents of 53 genotyped families).

• 1) 

  Three haplotypes or segments of them (A2, Cw3, B15, BfS, DR4; Aw30, Cw5, B18, BfF I, DR3; and Al, Cw7, B8, BfS, DR3) were found more frequently in IDD patients.
• 2) 

  Measured by the 6 formula, the association of the postulated IDD susceptibility gene was very strong with the D-end of two of these haplotypes: BfF1, DR3 and BfS, DR4. However, the association was weak with the DR3 of the haplotype Al, Cw7, B8, BfS, DR3.
• 3) 

  An excess of HLA-identical affected siblings was found.
• 4) 

  An excess of DR3/DR4 heterozygotes was observed. By contrast, the observed frequency of patients homozygous for DR3 or DR4 was not increased, but even slightly decreased.

The data support a model of inheritance comprising at least two closely linked specifically "diabetic" loci (most of the time marked by B18, BfFl, DR3 and B15, BfS, DR4) and a non-specifically "diabetic" haplotype favouring auto-immunisation (most of the time marked by B8, BfS, DR3). This model is discussed in the light of the presented data and of those of the literature.     

HLA-DR2 in two sibships with insulin-dependent diabetes mellitus.

We report two families selected from 124 genotyped Caucasian insulin-dependent diabetes mellitus (IDDM) families because of unusual features. In both families, all offspring are affected and four out of six bear the allele HLA-DR2 which is an uncommon phenotype among diabetic patients. Onset before the age of 1 year in all the patients of one family, association with optic atrophy in the other, and the existence of pairs of affected sibs of different HLA types in both, are infrequent findings and support the evidence of heterogeneity in IDDM.     

Chronic non-insulin deficient hyperglycemia in children

We report the clinical records of 45 children with abnormalities regarding glycemic regulation characterized by a non-insulin deficient hyperglycemia (NIDH), known under the different names of chemical diabetes, sub-clinical diabetes and more recently MODY. These 45 children belong to 31 families with 532 relatives comprising 137 cases of NIDH which could have been studied. The symptoms of this biochemical abnormality, the pathophysiology of which is not yet clearly understood, are the following: lack of clinical manifestations, except for a variable and intermittent glycosuria; constant abnormal glucose tolerance tests, above 97 percentiles of the reference value with some variations over time; normal immunoreactive insulin levels; percentage of glycosylated hemoglobin at the upper range of normal; dominant autosomal genetic transmission and no association with HLA markers like in insulin-dependent diabetes; lack of degenerative complications of the micro-angiopathic type, at least on these cases even after more than 30 years of follow-up; finally, no tendency towards insulin-dependent diabetes. The NIDH should not be confused with the slow and progressive beginning of insulin-dependent diabetes for which prolonged delay is needed to affirm the diagnosis. The frequency of the biochemical phenomena is about 1.8% of the cases of authentic diabetes mellitus occurring before the age of 15.