Transferrin microheterogeneity in rats treated chronically with ethanol

A PMM2-CDG caused by an A108V mutation associated with a heterozygous 70 kilobases deletion case report

Background

Congenital Disorders of Glycosylation (CDG) are a large group of inborn errors of metabolism with more than 140 different CDG types reported to date (1). The first characterized, PMM2-CDG, with an autosomal recessive transmission, is also the most frequent. The PMM2 gene encodes a phosphomannomutase. Here, a novel genetic variation causing PMM2-CDG is reported. 

Case presentation

We report the case of a French child, from healthy and unrelated parents, presenting congenital ataxia with hypotonia, hyperlaxity, inverted nipples, as well as altered coagulation parameters and liver function. Transferrin isoelectrofocusing revealed a typical type I CDG profile. Direct Sanger sequencing and quantitative PCR of PMM2 revealed a unique and novel genotype. On one allele, the patient was heterozygote with a known missense variant NM_000303.3(PMM2):c.323C > T, p.Ala108Val in exon 4. On the second allele, whole genome sequencing (WGS) indicated the presence of a novel heterozygous 70 kb deletion.

Conclusion

We report in the present paper the largest known heterozygous deletion of a PMM2 gene. The observation reveals the impact of a precise diagnostic on genetic counselling: by using WGS, an erroneous conclusion of homozygosity in the case of a relatively rare variant could be avoided, and an index patient with healthy and unrelated parents correctly identified.

Iron uptake from transferrin and asialotransferrin by hepatocytes from chronically alcohol-fed rats

Chronic alcohol intake is often associated with alterations to iron homeostasis and an increase in the serum levels of carbohydrate-deficient transferrin. As the liver is a major iron storage site and also synthesizes transferrin, the normal serum iron transport protein, the aim of this study was to test the hypothesis that these disturbances in iron homeostasis were caused by altered hepatocyte iron uptake from the abnormal transferrin. To achieve this, we have investigated iron uptake from both transferrin and asialotransferrin by hepatocytes from male Sprague-Dawley rats fed the De Carli and Lieber alcohol diet. Iron uptake from transferrin by hepatocytes from alcoholic rats was less than 60% that of control values, and in the presence of 50 mM ethanol decreased still further to 35% of the uptake by the corresponding control cells. Iron uptake from rat asialotransferrin was reduced in both groups when compared to that observed from normal transferrin; 13% by control cells and 39% by hepatocytes from alcohol-fed rats. Alcohol, however, had no further effect on asialotransferrin uptake by either hepatocytes from alcohol-fed rats, or their pair-fed controls. Transferrin binding to hepatocytes was also influenced by the alcohol diet. Although there was no difference in binding at 37 degrees C, cells from alcohol-fed rats bound 85% of this total at 4 degrees C, compared to 44% by control hepatocytes. Similar values were also obtained for hepatocyte binding of asialotransferrin; alcohol feeding resulted in an increase in binding at 4 degrees C to 73% from 58% with control cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Laboratory markers of ethanol intake and abuse: a critical appraisal

Laboratory markers for ethanol intake and abuse and chronic alcoholism currently in use have been critically reviewed. The merits and pitfalls of each test have been evaluated. The clinical use of the new test of carbohydrate-deficient transferrin has been particularly emphasized. Carbohydrate-deficient transferrin currently provides the highest specificity and sensitivity of all commonly used markers of alcoholism.

The effect of ethanol metabolism on ferritin uptake by freshly isolated rat hepatocytes: is acetaldehyde responsible for this alteration?

Alcohol abuse is associated with disturbances to iron metabolism in man, ranging from anemia to siderosis. Also seen in these patients are increased serum ferritin levels. Since the liver not only stores iron in cytosolic ferritin, but has also been shown to take up this molecule from the plasma by an active transport mechanism, it has been suggested that the iron in this circulating ferritin may contribute to the increased incidence of siderosis seen in alcoholics. As part of an ongoing study of these disturbances, using a rat model, we have examined the uptake of ferritin by freshly isolated hepatocyte suspension to test the hypothesis that increased hepatocyte uptake of ferritin iron contributes to the siderosis seen in some alcoholics. Incubation of hepatocytes in the presence of ethanol resulted in a progressive reduction in uptake with increasing alcohol concentration, from 1.23 +/- 0.05 ng of ferritin/10(6) cells/min to 0.65 +/- 0.02 ng/10(6) cells/min (mean +/- SD) at an ethanol concentration of 100 mM. 4-Methylpyrazole (0.1 mM) restored 70% of this activity, but higher concentrations also decreased ferritin uptake in the absence of ethanol. The addition of 5 microM cyanamide decreased ferritin uptake slightly in the presence of ethanol (0.82 +/- 0.04 ng of ferritin/10(6) hepatocytes/min vs. 0.86 +/- 0.03 ng/10(6) cells/min for ethanol alone), while having no effect in the absence of ethanol (1.01 +/- 0.04 vs. 1.12 +/- 0.05 ng/10(6) cells/min). Preincubation of the hepatocytes with acetaldehyde resulted in a dose-dependent reduction to a maximum reduction of approximately 25% at 300 microM acetaldehyde.(ABSTRACT TRUNCATED AT 250 WORDS)