Varda Barash

Neurologic Presentations of Mitochondrial Disorders

This article describes the neurologic presentations of children with mitochondrial disorders. The charts of 42 children with highly suspect mitochondrial disorders were reviewed. Thirty-seven children were diagnosed as having definite mitochondrial disorders based on a suggestive clinical presentation and at least one accepted criteria, while in five patients the diagnosis remained probable. All patients had nervous system involvement, but it was the presenting symptom in 28 of 42. Eighteen children had normal intelligence and 24 had mental retardation or developmental delay at the onset of their disease. Twenty-five patients had either an acute regression or a progressive encephalopathy. The most frequent neurologic manifestations were abnormal tone, seizures, extrapyramidal movements, and autonomic dysfunction. The eyes were involved in 11 children. Nerve deafness was found in seven patients. Myopathy was found in only six patients. In conclusion, a complex neurologic picture, especially with other organ involvement, warrants a full mitochondrial evaluation. (J Child Neurol 2000; 15:44-48).

Adult polyglucosan body disease: Natural History and Key Magnetic Resonance Imaging Findings.

Adult polyglucosan body disease (APBD) is an autosomal recessive leukodystrophy characterized by neurogenic bladder, progressive spastic gait, and peripheral neuropathy. Polyglucosan bodies accumulate in the central and peripheral nervous systems and are often associated with glycogen branching enzyme (GBE) deficiency. To improve clinical diagnosis and enable future evaluation of therapeutic strategies, we conducted a multinational study of the natural history and imaging features of APBD.

Placental Function in Maternal-Fetal Fat Transport in Diabetes

High levels of triglycerides (TG) and free fatty acids (FFA) in maternal plasma, in diabetes, promote fat passage to the fetus. In the streptozotocin-diabetic rat a significant correlation exists between maternal plasma and fetal tissue lipid contents, as shown by the accretion of labeled fatty acids or linoleate used as markers of maternal fat transfer. The passage of lipids through the placenta is not direct--this organ serves as an interim storage barrier with its lipid content increasing in proportion to the maternal TG and FFA level. Very low density lipoprotein (VLDL) TG are taken up with the aid of lipoprotein lipase as evident from TG = glycerol exchange when doubly labeled VLDL-TG are presented to the placenta. Esterification rate of albumin-bound FFA is considerably higher indicating that the rate of TG lipolysis is rate limiting and that the FFA are the main precursor of the placental lipids. The uptake of both FFA and VLDL-TG is associated with the retention of a substantial amount of FFA in the placenta. The size of the FFA pool corresponds to the size of the extracellular fluid space. The FFA cannot be eluted by repeated washing, suggesting that they are membrane bound. Placental slices with prelabeled TG gradually release FFA into the medium upon reincubation with FFA-free albumin, indicating that TG and FFA traverse the placenta in part by a sequential process of esterification and lipolysis and in part by diffusion as FFA. The latter are probably moving from the maternal to the fetal side within the interfacial capillary membrane lipids.

Multiple presentation of mitochondrial disorders

The aim of this study was to assess the heterogeneous clinical presentations of children with mitochondrial disorders evaluated at a metabolic neurogenetic clinic. The charts of 36 children with highly suspected mitochondrial disorders were reviewed. Thirty one children were diagnosed as having a mitochondrial disorder, based on a suggestive clinical presentation and at least one of the accepted laboratory criteria; however, in five children with no laboratory criteria the diagnosis remained probable. All of the patients had nervous system involvement. Twenty seven patients also had dysfunction of other systems: sensory organs in 15 patients, cardiovascular system in five, gastrointestinal system in 20, urinary system in four, haematopoietic system in four, and endocrine system in nine. The clinical presentation was compatible with an established syndrome in only 15 children. Severe lactic acidosis or ragged red muscle fibres were encountered in very few patients. These results suggest that mitochondrial disorders should be evaluated in children presenting with a complex neurological picture or multisystem involvement. Key messages A full mitochondrial evaluation is warranted in children with a complex neurological picture or a single neurological symptom and other system involvement When the presentation is classic for a maternally inherited mitochondrial syndrome—for example, mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), myoclonic epilepsy and ragged red muscle fibres (MERRF), Leber’s hereditary optic neuropathy (LHON), appropriate mitochondrial DNA studies should be obtained first When the clinical picture is classic for a nuclear DNA inherited syndrome and the gene or the linkage is known—for example, MNGIE (mitochondrial neurogastrointestinal encephalopathy) or DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy, and deafness), proceed with genetic studies When the clinical picture is non-specific but highly suggestive of a mitochondrial disorder, start with serum and/or cerebrospinal fluid lactic acid and urinary organic acids and proceed with muscle biopsy and assessment of the respiratory chain enzymes Normal serum or cerebrospinal fluid lactic acid does not exclude a mitochondrial disorder

Mechanism of placental glycogen deposition in diabetes in the rat

SummaryThe metabolic basis for glycogen accumulation in the placenta of rats with diabetes induced by streptozotocin on day 12 of pregnancy was studied on days 15 and 20. On day 15 glycogen content of the placenta was 1.5-fold higher in the diabetic than in the control rats and this difference increased to > fivefold on day 20 of gestation whether calculated per g tissue or per total placenta. Accumulation of glycogen was associated with increased specific activities of both glycogen synthase and phosphorylase. The activities of these enzymes regulating synthase and phosphorylase activities and the activity of acid α-glucosidase were not significantly affected by diabetes. Glucose-6-phosphate concentration of the placenta was 67 and 23 nmol/g in diabetic and control rats, respectively. Incubation of placental homogenates with glucose increased the rate of inactivation of phosphorylase and activation of glycogen synthase. These results indicate that the enhanced glucogenesis in diabetes is not due to changes in the activities of these enzymes, as measured in vitro under standard conditions. The factors promoting glycogen accumulation in vivo are related to the abundance of glucose and glucose-6-phosphate as substrates for glycogen synthesis, which may also cause an increase in the activity ratio glycogen synthase a/ phosphorylase a. In addition, the high intracellular glucose-6-phosphate concentration is likely to enable glycogen synthase b to contribute to glycogen synthesis.

MEHMO (Mental retardation, Epileptic seizures, Hypogenitalism, Microcephaly, Obesity): a new X-linked mitochondrial disorder

MEHMO (Mental retardation, Epileptic seizures, Hypogenitalism, Microcephaly and Obesity) is an X-linked disorder characterised by mental retardation, epileptic seizures, hypogenitalism, microcephaly and obesity. It was recently assigned to the locus Xp21.1-p22.13. We describe a child with MEHMO and lactic acidosis whose muscle biopsy revealed markedly reduced activities of complexes 1,3 and 4 of the mitochondrial electron transport chain. Histological staining showed mitochondrial proliferation and lipid storage. Electron microscopy revealed abnormal and enlarged mitochondria with concentric cristae and electron dense bodies. This is the first identification of MEHMO as a mitochondrial disorder and one of the very few X-linked mitochondrial syndromes.

Kinetic and immunologic evidence for the absence of glucose-6-phosphatase in early human chorionic villi and term placenta

The existence of the enzyme glucose-6-phosphatase (G6Pase) in early and term human placenta was investigated by comparing the characteristics of placental microsomal glucose 6-phosphate (G6P) hydrolytic activity and liver G6Pase. Placental microsomes exhibited similar apparent Km values for G6P and beta-glycerophosphate in intact and deoxycholate-treated microsomes, heat stability at acidic pH, low latency of mannose 6-phosphate hydrolysis, very low activity of pyrophosphate: glucose phosphotransferase, and undetectable [U-14C]G6P transport into the placental microsomes, all of which indicated that specific G6Pase activity does not exist in placenta. Immunological evidence of the absence of both 36.5 kDa and T2 proteins, which represent the G6Pase catalytic protein and the phosphate/pyrophosphate transporter protein, respectively, confirmed that early and term human placenta are devoid of the multicomponent G6Pase enzyme.

Lethal hypoglycemia and hypothermia induced by administration of low doses of tumor necrosis factor to adrenalectomized rats

An increased sensitivity of adrenalectomized (Adex) rats to intravenous (IV) injection of recombinant human tumor necrosis factor (rHuTNF) was manifested by a marked increase in the rate of mortality. The rats that died exhibited severe hypoglycemia and hypothermia. Administration of 2.5 or 10 micrograms/100 g body weight (3% or 12%) of the lethal dose in sham-operated rats (90 micrograms/100 g body weight) rHuTNF caused a mortality rate of 50% or 100%, respectively, within 4 hours of its injection. Pre-administration of dexamethasone or intermittent glucose infusion protected the animals from the lethal effect of rHuTNF. Indomethacin did not change the mortality rate in rHuTNF-treated Adex rats, but prevented it in sham-operated rats. The rats that died exhibited a marked decrease in body temperature, but only Adex rats developed hypoglycemia after low doses of TNF. Pretreatment with dexamethasone prevented the hypothermia in both Adex and sham-operated rats, while indomethacin was effective only in sham-operated rats and did not prevent the hypothermia or the hypoglycemia in Adex rats. In the surviving rHuTNF-treated Adex rats, a rapid increase in body temperature occurred, blood glucose decreased to 30 mg/dL, serum insulin concentration decreased to 6 microU/mL, liver glycogen content was reduced by 98%, and a significant reduction in liver phosphoeonolpyruvate carboxykinase (PEPCK) and liver microsomal glucose-6-phosphatase activities was observed. Repeated administration of glucose IV to rHuTNF-treated Adex rats caused an increase in blood glucose and insulin concentrations, and some repletion in liver glycogen content. Injection of rHuTNF, 2.5 to 10 micrograms/100 g body weight, to sham-operated rats caused a significant but slower increase in body temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal diabetes in rats and its effect on placental glycogen.

SummaryThe role of fetal insulin in placental glycogen accumulation, which occurs despite insulin deficiency in maternal diabetes, was studied in rats. Streptozotocin was injected into fetuses of non-diabetic and streptozotocin-diabetic mothers on days 19.5 and 20.5 of gestation, causing fetal hypoinsulinaemia and pancreatic insulin depletion. Placental glycogen content of either 1.6 mg/g in non-diabetic rats or 6.5 mg/g in diabetic rats was not affected by fetal streptozotocin treatment. Glycogen distribution was also measured in the placenta to assess the effect of fetal hypoinsulinaemia on glycogen content in its fetal segment. The glycogen concentration ratio between the fetal and maternal segments in diabetic rats was ∼0.3 and increased to ∼0.5 in diabetic rats, without being affected by fetal hypoinsulinaemia. There was no significant effect of fetal hypoinsulinaemia on the activities of placental glycogen synthase or glycogen phosphorylase, both in nondiabetic and diabetic rats. Fetal hypoinsulinaemia was associated, however, with a marked decrease in fetal liver glycogen together with a decrease in fetal liver weight, which was more pronounced than the decrease in fetal body weight. Administration of insulin to the streptozotocin-treated fetuses restored the impaired glycogen synthesis (measured by incorporation of U-[14C]-glucose and 3H2O in the fetal liver) without affecting glycogen synthesis in the placenta. These results demonstrate: (1) placental glycogen metabolism in contrast to fetal liver glycogen metabolism, is not regulated by fetal insulin; (2) the reduced fetal liver weight and its glycogen content, rather than hyperglycaemia, are the salient features of fetal insulin deficiency; and (3) placental glycogen accumulation in diabetes is related to the hyperglycaemia of maternal origin and not to the changes in maternal or fetal insulin availability.

Tumor necrosis factor inhibits the transcriptional rate of glucose-6-phosphatase in vivo and in vitro

Recombinant human tumor necrosis factor-alpha (TNF) injection in mice was associated with a reduced blood glucose level, already manifest 6 hours following cytokine administration. Insulin levels were not affected. Glycogen content was decreased in a dose-dependent and time-response manner. The activity of glucose-6-phosphatase (G6Pase) was already reduced 6 hours after TNF injection and was sustained 12 hours afterward. Phosphoenolpyruvate carboxykinase (PEPCK) activity was not affected initially (6 hours after injection), but a 50% reduction was observed 12 hours following cytokine administration compared with levels in fasting controls. Both liver G6Pase and PEPCK mRNAs were markedly reduced due to an inhibition of the transcriptional rate. A direct inhibitory effect of TNF on G6Pase promoter activity was demonstrated using HuH-7 cells transiently transfected with G6Pase promoter, fused to a reporter gene.