The implications of genetic diversity for nutrient requirements: the case of folate

"The existence of chemical individuality follows of necessity from that of chemical specificity, but we should expect the differences between individuals to be still more subtle and difficult of detection. Indications of their existence are seen, even in man,... in the quantitative differences in those portions of the end products of metabolism which are endogenous and are not affected by diet.... Even those idiosyncracies with regard to... articles of food which are summed up in the proverbial saying that what is one's man meat is another man's poison, presumably have a chemical basis."

Hyperhomocysteinaemia and associated disease

An elevated plasma homocysteine level may result from various environmental and genetic factors. Herediatary causes of severe hyperhomo-cysteinaemia are very rare and usually lead to disease in childhood or adolescence. Common pathology consists of early atherosclerotic vascular changes, arterioocclusive complications and venous thrombosis. Mildly elevated genetically determined plasma homocysteine levels are observed in 5% of the general population. In the last two decades research has shown mild hyperhomocysteinaemia to be linked to an increased risk of premature atherosclerosis, pregnancies complicated by neural tube defects and early pregnancy loss, and venous thrombosis. Homozygosity for thermolabile MTHFR deficiency has been identified as one important genetic factor, which expression is modified by dietary folate intake. Although mild hyperhomocysteinaemia can easily be treated by vitamin supplementation the beneficial effects of such treatment remains to be shown.

Ceruloplasmin gene expression in the murine central nervous system

Aceruloplasminemia is an autosomal recessive disorder resulting in neurodegeneration of the retina and basal ganglia in association with iron accumulation in these tissues. To begin to define the mechanisms of central nervous system iron accumulation and neuronal loss in this disease, cDNA clones encoding murine ceruloplasmin were isolated and characterized. RNA blot analysis using these clones detected a 3.7-kb ceruloplasmin-specific transcript in multiple murine tissues including the eye and several regions of the brain. In situ hybridization of systemic tissues revealed cell-specific ceruloplasmin gene expression in hepatocytes, the splenic reticuloendothelial system and the bronchiolar epithelium of the lung. In the central nervous system, abundant ceruloplasmin gene expression was detected in specific populations of astrocytes within the retina and the brain as well as the epithelium of the choroid plexus. Analysis of primary cell cultures confirmed that astrocytes expressed ceruloplasmin mRNA and biosynthetic studies revealed synthesis and secretion of ceruloplasmin by these cells. Taken together these results demonstrate abundant cell-specific ceruloplasmin expression within the central nervous system which may account for the unique clinical and pathologic findings observed in patients with aceruloplasminemia.

Neuropathology and pathogenesis of mitochondrial diseases

The majority of patients with mitochondrial disease have significant neuropathology, with the most common features being spongiform degeneration, neuronal loss and gliosis. Although there is considerable overlap between different mitochondrial diseases, the nature and distribution of the lesions is sufficiently distinctive in some cases to suggest a specific diagnosis. On the other hand, a number of different defects in cerebral energy metabolism are associated with common patterns of neuropathology (e.g. Leigh syndrome), suggesting that there is a limited range of responses to this type of metabolic disturbance. There are many descriptions of neuropathological changes in patients with mitochondrial disease, but there has been remarkably little investigation of the underlying pathogenic mechanisms. Comparisons with other conditions of cerebral energy deprivation such as ischaemia/hypoxia and hypoglycaemia suggest a possible role for excitotoxicity initiated by excitatory amino acid neurotransmitters. An additional contributing factor may be peroxynitrite, which is formed from nitric oxide and the oxygen free radicals which accumulate with defects of the mitochondrial electron transport chain. Mitochondrial diseases are often characterized by episodes of neurological dysfunction precipitated by intercurrent illness. Depending on the severity of the metabolic abnormality, each of these episodes carries a risk of further neuronal death and the result is usually progressive accumulation of irreversible damage. The balance between reversible functional impairment and neuronal death during episodes of metabolic imbalance is determined by the effectiveness of various protective mechanisms which may act to limit the damage. These include protective metabolic shielding of neurons by astrocytes and suppression of electrical activity (and hence energy demands) by activation of ATP-gated ion channels. In addition, recent evidence suggests that lactic acid, the biochemical abnormality common to these conditions, may not be toxic at moderately high concentrations but may in fact be protective by reducing the sensitivity of neurons to excitotoxic mechanisms.

[A predictive and prognostic study on two cases of transient hyperphosphatasemia of infancy]

We presented two cases with transient hyperphosphatasemia (TH) of infancy, whose serum alkaline phosphatase (EC 3.1.3.1, ALP) activity showed markedly increased and the atypical isoenzyme fractions were seen by electrophoresis. These isoenzymes migrated into normal bone ALP region (alpha 2-beta globulin fraction) and fast liver ALP region (fast alpha 2 globulin fraction). From various investigation such as, heat stability, inhibition test by amino acid, neuraminidase treatment and Triton X-100 treatment, former fraction seemed to derive from bone ALP and later fraction from liver ALP. From our study, increment of the activity of alpha 2-beta gl fraction was in advance one month before maximum ALP activity stage, and fast alpha 2 gl fraction followed increasing 3 weeks after that. On the other hand, decreasing of fast alpha 2 gl fraction showed a shorter delay than alpha 2-beta gl fraction. These results suggest that a differential exchange of sugar chain or an impaired clearance of the enzyme from circulation was possibly occurred. It seemed to be important to increase a study of such a predictive and prognostic change of ALP activity and isoenzyme fraction in TH cases.

Familial giant cell hepatitis with low bile acid concentrations and increased urinary excretion of specific bile alcohols: a new inborn error of bile acid synthesis?

A 9-wk-old infant with familial giant cell hepatitis and severe intrahepatic cholestasis had low plasma concentrations of chenodeoxycholic acid and cholic acid and elevated plasma concentrations of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrol, 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24 zeta-tetrol, and 5 beta-cholest-24-ene-3 alpha,7 alpha,12 alpha-triol. Analysis of the urine by fast atom bombardment mass spectrometry and by gas chromatography-mass spectrometry after treatment with Helix pomatia glucuronidase/sulfatase showed that the major cholanoids in urine were the glucuronides of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24S,25-pentol, 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrol, and 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24 zeta-tetrol. These results are consistent with an inborn error of the 25-hydroxylase pathway for bile acid synthesis, specifically one of the enzymes responsible for conversion of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24S,25-pentol to cholic acid and acetone. Treatment with chenodeoxycholic acid was tried on two occasions. On the first it appeared to precipitate a rise in bilirubin, on the second the liver function tests improved and the improvement was maintained when the treatment was modified to a combination of chenodeoxycholic acid and cholic acid and finally, cholic acid alone. Despite the normalization of liver function tests, a liver biopsy at 1.25 y showed an active cirrhosis. Nonetheless, the child is thriving at the age of 3.5 y, whereas an affected sibling died at 13 mo.

Inhibition of mitochondrial beta-oxidation as a mechanism of hepatotoxicity

Severe and prolonged impairment of mitochondrial beta-oxidation leads to microvesicular steatosis, and, in severe forms, to liver failure, coma and death. Impairment of mitochondrial beta-oxidation may be either genetic or acquired, and different causes may add their effects to inhibit beta-oxidation severely and trigger the syndrome. Drugs and some endogenous compounds can sequester coenzyme A and/or inhibit mitochondrial beta-oxidation enzymes (aspirin, valproic acid, tetracyclines, several 2-arylpropionate anti-inflammatory drugs, amineptine and tianeptine); they may inhibit both mitochondrial beta-oxidation and oxidative phosphorylation (endogenous bile acids, amiodarone, perhexiline and diethylaminoethoxyhexestrol), or they may impair mitochondrial DNA transcription (interferon-alpha), or decrease mitochondrial DNA replication (dideoxynucleoside analogues), while other compounds (ethanol, female sex hormones) act through a combination of different mechanisms. Any investigational molecule should be screened for such effects.

[Liver pathologies due to peroxisome disorders]

Peroxisomes or microbodies are peculiar subcellular organelles with an important role in the metabolism of a variety of different organic compounds. Particularly they are an important site of bile acids synthesis. Some hepatic diseases, mainly cholestatic, can to be reconnected at disorders of bile acids synthesis by these organelles. From the biochemical point some diseases present alterations of the cholesterol side chain (Zellweger syndrome, pseudo-Zellweger syndrome, infantile Refsum's disease, neonatal adrenoleukodystrophy), other diseases present errors involving the steroid nucleus (familial giant cell hepatitis). Zellweger disease or cerebro-hepato-renal syndrome is characterized clinically by skeletal changes, muscle hypotonia, renal cysts, psychosomatic retardation and persistent cholestasis and from the ultrastructural standpoint by the virtual absence of liver cell peroxisomes. Pseudo-Zellweger disease shows many of the clinical features of Zellweger disease but differs from this condition on account of the presence of abundant peroxisomes in the liver cells. Infantile Refsum's disease and neonatal adrenoleukodystrophy show typical clinical disorders and liver damage leading to cirrhosis. "Familial giant cell hepatitis" is characterized by jaundice from the first days of life, hepatosplenomegaly, cholestasis, lack of physical malformations. The disorder is due to defective biosynthesis of the bile acids with formation of allo-bile acids.

Quinolinate in brain and cerebrospinal fluid in rat models of congenital hyperammonemia

Children with inborn errors of urea synthesis who survive neonatal hyperammonemic coma commonly exhibit cognitive deficits and neurologic abnormalities. Yet, there is evidence that ammonia is not the only neurotoxin. Hyperammonemia appears to induce a number of neurochemical alterations. In rodent models of hyperammonemia, uptake of L-tryptophan into brain is increased. It has been reported that in an experimental rat model of hepatic encephalopathy, in the ammonium acetate-injected rat, and in patients with hepatic failure and inborn errors of ammonia metabolism, quinolinate, a tryptophan metabolite, is increased. Elevations in quinolinate are of particular concern, as quinolinate could excessively activate the N-methyl-D-aspartate subclass of excitatory amino acid receptors, thereby causing selective neuronal necrosis. We sought to identify an animal model that would replicate the increases in quinolinate that have been associated with hyperammonemia in humans. Levels of quinolinate were measured in hyperammonemic urease-infused rats and ammonium acetate-injected rats. In the urease-infused rat, brain tryptophan was doubled, and serotonin and its metabolite 5-hydroxyindoleacetic acid were significantly increased. Yet, despite the increase in tryptophan and evidence for increased metabolism of tryptophan to serotonin, there were no observed increases of quinolinate in brain, cerebrospinal fluid, or plasma. In the ammonium acetate-injected rat, significant increases of 5-hydroxyindoleacetic acid in cerebral cortex were also observed, but quinolinate did not change in cerebrospinal fluid or cerebral cortex. In summary, we were unable to demonstrate an increase of quinolinate in brain or cerebrospinal fluid in these rat models of hyperammonemia.

Molecular basis of mitochondrial fatty acid oxidation defects

A dozen separate inherited disorders of mitochondrial fatty acid beta-oxidation have been described in humans. This represents about half of the potential sites for genetic error that can affect this important pathway of energy metabolism. As the characterization of these disorders at the clinical and biochemical levels has progressed rapidly, so has the delineation of the molecular defects that underlie them. The most commonly recognized disorder of beta-oxidation is medium-chain acyl-CoA dehydrogenase deficiency; a striking feature of this disorder is that there is a single point mutation that accounts for 90% of the variant alleles among patients with medium-chain acyl-CoA dehydrogenase deficiency. Molecular defects of other enzymes in the pathway have been identified, and it seems likely that a complete description of these defects at the molecular level is a realistic goal. In basic biological terms, such studies will lead to a better understanding of the genetic control exerted on this pathway. In clinical terms, they will lead to improved understanding of the molecular pathophysiology of these diseases and may well provide the necessary techniques to proceed with the screening of these disorders.

The peroxisome and the eye

Several childhood multisystem disorders with prominent ophthalmological manifestations have been ascribed to the malfunction of the peroxisome, a subcellular organelle. The peroxisomal disorders have been divided into three groups: 1) those that result from defective biogenesis of the peroxisome (Zellweger syndrome, neonatal adrenoleukodystrophy, and infantile Refsum's disease); 2) those that result from multiple enzyme deficiencies (rhizomelic chondrodysplasia punctata); and 3) those that result from a single enzyme deficiency (X-linked adrenoleukodystrophy, primary hyperoxaluria type 1). Zellweger syndrome, the most lethal of the three peroxisomal biogenesis disorders, causes infantile hypotonia, seizures, and death within the first year. Ophthalmic manifestations include corneal opacification, cataract, glaucoma, pigmentary retinopathy and optic atrophy. Neonatal adrenoleukodystrophy and infantile Refsum's disease appear to be genetically distinct, but clinically, biochemically, and pathologically similar to Zellweger syndrome, although milder. Rhizomelic chondrodysplasia punctata, a peroxisomal disorder which results from at least two peroxisomal enzyme deficiencies, presents at birth with skeletal abnormalities and patients rarely survive past one year of age. The most prominent ocular manifestation consists of bilateral cataracts. X-linked (childhood) adrenoleukodystrophy, results from a deficiency of a single peroxisomal enzyme, presents in the latter part of the first decade with behavioral, cognitive and visual deterioration. The vision loss results from demyelination of the entire visual pathway, but the outer retina is spared. Primary hyperoxaluria type 1 manifests parafoveal subretinal pigment proliferation. Classical Refsum's disease may also be a peroxisomal disorder, but definitive evidence is lacking. Early identification of these disorders, which may depend on recognizing the ophthalmological findings, is critical for prenatal diagnosis, treatment, and genetic counselling.

[Neonatal complications in infants born to mothers with diabetes mellitus]

Health status of 53 babies delivered by diabetic mothers are discussed. Neonatal period was uncomplicated only in 12 cases. The remaining babies suffered from respiratory disorders, edema, neurological disturbances, prolonged jaundice, infections etc. Metabolic disorders in diabetic female are unfavourable for the development of pregnancy and neonate health. it may be improved by the proper diagnostico-therapeutical management prior to and during pregnancy and by intensive care of neonates after delivery. It requires, however, the establishment of health institution with highly qualified teams well equipped which will be able to carry out diagnosis and therapy of diabetes mellitus in females in the reproductive age, during pregnancy as well as proper care of the neonates.

Clinical approach to inherited metabolic disorders in neonates

Most inborn errors of intermediary metabolism presenting in the neonatal period fall schematically into three clinical categories: (1) those which lead to a neurological distress 'intoxication type' with a symptom-free interval, vomiting, comas, hypertonia, abnormal movements and frequent humoral disturbances (organic acidaemias, congenital urea cycle defects); (2) those which lead to a neurological distress 'energy deficiency' type. Frequent symptoms in this group include hyperlactacidaemia, severe hypotonia, cardiomyopathy, failure to thrive and malformations (congenital lactic acidaemias, fatty acid oxidation defects, peroxysomal disorders); (3) those which present evidence of liver dysfunction and hepatomegaly (glycogenesis, neoglucogenesis defects, galactosaemia, fructosaemia, tyrosinaemia type I). According to these three major clinical presentations and according to the proper use of few screening tests (blood gases, glucose, ammonia, lactic acid, electrolytes, acetest), we propose a method of diagnosis which groups these children into five schematical syndromes: type I MSUD; type II organic acidaemias; type III; congenital lactic acidosis; type IVa, urea cycle defects; type IVb, non-ketotic hyperglycinaemia, sulfite oxidase deficiency, peroxisomal disorders; type V liver dysfunctions. Once the above classification has been made, sophisticated and specific investigations can be planned (amino acid chromatography, organic acid chromatography, enzymatic studies, etc).

[New perspectives in liver-based metabolic errors: liver transplantation]

Liver transplantation offers an actual alternative to patients end-stage liver disease. The aim of this study is to show our results of liver transplantation in paediatric patients with hepatic-based metabolic disorders. Survival rates in these indications can be high and these good results may enlarge the indications. Liver might transplantation therefore be offered earlier to patients with this kind of metabolic disease.