Hereditary fructose intolerance

Hereditary fructose intolerance (HFI, OMIM 22960), caused by catalytic deficiency of aldolase B (fructose-1,6-bisphosphate aldolase, EC 4.1.2.13), is a recessively inherited condition in which affected homozygotes develop hypoglycaemic and severe abdominal symptoms after taking foods containing fructose and cognate sugars. Continued ingestion of noxious sugars leads to hepatic and renal injury and growth retardation; parenteral administration of fructose or sorbitol may be fatal. Direct detection of a few mutations in the human aldolase B gene on chromosome 9q facilitates the genetic diagnosis of HFI in many symptomatic patients. The severity of the disease phenotype appears to be independent of the nature of the aldolase B gene mutations so far identified. It appears that hitherto there has been little, if any, selection against mutant aldolase B alleles in the population: in the UK, approximately 1.3% of neonates harbour one copy of the prevalent A149P disease allele. The ascendance of sugar as a major dietary nutrient, especially in western societies, may account for the increasing recognition of HFI as a nutritional disease and has shown the prevalence of mutant aldolase B genes in the general population. The severity of clinical expression correlates well with the immediate nutritional environment, age, culture, and eating habits of affected subjects. Here we review the biochemical, genetic, and molecular basis of human aldolase B deficiency in HFI, a disorder which responds to dietary therapy and in which the principal manifestations of disease are thus preventable.

Protoporphyria

Human protoporphyria results from mutations in the ferrochelatase gene. Heritable deficiency of ferrochelatase causes overproduction of protoporphyrin IX, principally in the erythron. Photosensitivity is a universal feature of protoporphyria but hepatic clearance of the hydrophobic protoporphyrin molecule with excretion in bile may lead to precipitation within biliary pathways. Thus cholestatic injury and protoporphyrin gallstones occur. Minor hepatic abnormalities are frequent, but at least 30 patients have been reported with a progressive liver disease that requires transplantation. Fulminant hepatic disease appears to be recessively inherited in some pedigrees. Hazards of liver transplantation include tissue photolysis, hemolysis, and an unexplained neurological syndrome, but most of the 15 patients reported after transplantation have survived for several months to > 6 years. Aspects of protoporphyria, its pathogenesis and contemporary therapeutic strategies are considered, with emphasis on hepatic sequelae.

Gaucher's disease: clinical features and natural history

Gaucher's disease is an inherited disorder characterized by pathological storage of glycolipid in mononuclear phagocytes: it is a multi-system disease associated with striking variation in its clinical manifestations, severity and course. Although molecular analysis of the glucocerebrosidase gene in patients with Gaucher's disease has permitted broad correlations between genotype and phenotype to be made, with few exceptions genetic variation at this locus does not allow confident prediction of clinical phenotype or prognosis. Partial deficiency of glucocerebrosidase is associated principally with parenchymal disease of the liver, spleen, bone marrow and, in severe cases, the lung, in non-neuronopathic, Type 1, Gaucher's disease: here storage material in macrophages originates from turnover of exogenous glycolipids. Severe deficiency of glucocerebrosidase caused by disabling mutations is additionally associated with neurological manifestations that in part reflect a failure to degrade endogenous neuronal glycosphingolipids, the so-called neuronopathic, Type 2 and Type 3 disease categories. Here we describe the clinical features, complications and natural history principally of Type 1 Gaucher's disease: emphasis is placed on emerging pulmonary, osseous and other manifestations of obscure pathogenesis that respond poorly to enzyme-replacement therapy.

Homozygosity for the predominant Cys282Tyr mutation and absence of disease expression in hereditary haemochromatosis

A candidate gene for hereditary haemochromatosis, HLA-H, has recently been presented. Two missense mutations in the HLA-H gene sequence are predicted to account for nearly 90% of all cases of the disease. The aim of this study was to correlate the presence of these missense mutations with the expressivity of the disease, as assessed by standard biochemical evaluation of serum iron parameters. Detection of the known mutations in haemochromatosis, Cys282Tyr and His63Asp, was undertaken in a large pedigree showing variable expression of the disease in successive generations. In three sibs with overt disease (one male, two female, aged 50 to 53 years), homozygosity for the predominant G to A transition (Cys282Tyr) in HLA-H was detected. However, homozygosity for this mutation was also detected in an asymptomatic male sib, aged 50, harbouring an identical genotype. The finding of an asymptomatic homozygous Cys282Tyr subject, haplo-identical to affected sibs, indicates that clinical expression of symptomatic disease is variable, even in middle aged Cys282Tyr homozygotes. This has profound implications for the future use of genetic screening for haemochromatosis.

Erythropoietic protoporphyria

Partial deficiency of the last enzyme of haem biosynthesis, ferrochelatase, leads to a distinct syndrome of photosensitivity caused by overproduction of protoporphyrin by erythropoietic tissue. Erythropoietic protoporphyria has an indeterminate pattern of inheritance and may be complicated by fulminating liver disease. The recent development of simple assays for ferrochelatase activity and cloning of the human ferrochelatase gene promises to shed light on the transmission of this disorder and may allow clinical expression of disease to be predicted. This review surveys the pathological features, genetics and treatment of porphyria.

Transglutaminase activity is increased in Alzheimer's disease brain

Transglutaminase is a calcium-activated enzyme that crosslinks substrate proteins into insoluble, often filamentous aggregates resistant to proteases. Because the neurofibrillary tangles in Alzheimer's disease have similar characteristics, and because tau protein, the major component of these tangles is an excellent substrate of transglutaminase in vitro, transglutaminase activity and levels were measured in control and Alzheimer's disease brain. Frozen prefrontal cortex and cerebellum samples from Alzheimer's disease and control cases matched for age and postmortem interval were used in the analyses. Total transglutaminase activity was significantly higher in the Alzheimer's disease prefrontal cortex compared to control. In addition the levels of tissue transglutaminase, as determined by quantitative immunoblotting, were elevated approximately 3-fold in Alzheimer's disease prefrontal cortex compared to control. To our knowledge, this is the first demonstration that transglutaminase is increased in Alzheimer's disease brain. There were no significant differences in transglutaminase activity or levels in the cerebellum between control and Alzheimer's disease cases. Because the elevation of transglutaminase in the Alzheimer's disease samples occurred in the prefrontal cortex, where neurofibrillary pathology is usually abundant, and not in the cerebellum, which is usually spared in Alzheimer's disease, it can be suggested that transglutaminase could be a contributing factor in neurofibrillary tangle formation.

Translational control of erythroid delta-aminolevulinate synthase in immature human erythroid cells by heme

Heme formation in immature erythroid cells is subject to end-product negative feedback control. Although studies with immature erythroid cells obtained from animals have shown that increased intracellular hemin inhibits the acquisition of iron from transferrin, our experiments with human reticulocytes indicate that feedback inhibition of heme biosynthesis is primarily regulated at one or more steps that lead to formation of the first committed precursor, delta-aminolevulinate (ALA). To identify the site of control of heme biosynthesis in the human erythron further, region-specific antibodies to human erythroid delta-ALA synthase (e-ALA synthase) were used to immunoprecipitate newly-synthesised enzyme from human reticulocytes after biosynthetic labelling. Low concentrations of exogenous hemin (30-35 microM) inhibited the biosynthetic labelling of mature erythroid ALA synthase that was detected by exon 4 peptide-specific antibodies and antibodies raised against the entire recombinant human erythroid ALA synthase molecule. Pulse-chase experiments after biosynthetic labelling indicated no differences in the effect of hemin on the turnover of the radiolabelled enzyme and hemin did not influence the distribution of precursor froms of the ALA synthase molecule. Parallel experiments using antibodies directed against human H-chain ferritin confirmed the specificity of the effects of hemin on translation of the e-ALA synthase mRNA. At the concentrations of hemin used to inhibit heme formation from 14C-glycine, no significant effects on the rate of overall protein synthesis were observed. We conclude that heme regulates synthesis of the first committed precursor of the porphyrin biosynthetic pathway in immature human erythroid cells by effects on the synthesis of the e-ALA synthase molecule. Although the mechanism of hemin action is unknown, it is apparently independent of 5'-iron-response elements and influences the translational activity of erythroid ALA synthase mRNA.

The tau protein in human cerebrospinal fluid in Alzheimer's disease consists of proteolytically derived fragments

Previous studies have shown that the levels of the microtubule-associated protein tau in the CSF of patients with Alzheimer's disease (AD) are elevated compared with age-matched controls. In spite of these findings, the nature of tau in CSF has not been well documented. In the present study, tau was immunoprecipitated from CSF of patients with AD or acute stroke, as well as normal elderly controls, followed by immunoblot analysis. In all cases, CSF tau consisted primarily of a band migrating at 26-28 kDa. In AD and stroke patients, several smaller tau fragments were also detected. No intact tau was detected in any of the CSF samples examined. Further immunoprecipitation studies showed that the majority of the tau fragments contained the amino terminus of the molecule. Treatment of CSF tau with alkaline phosphatase did not alter the electrophoretic properties of the fragments. These studies clearly demonstrate that CSF tau is truncated rather than intact.

Skeletal muscle weakness and dysphagia caused by acid maltase deficiency: nutritional consequences of coincident celiac sprue

BACKGROUND

A 30-year-old woman with celiac sprue had progressive weight loss, myalgia, limb-girdle weakness, and dysphagia.

METHODS AND RESULTS

Barium swallow showed an atonic esophagus, and scintigraphic study confirmed esophageal dysmotility. Skeletal muscle biopsy showed characteristic appearances of acid maltase deficiency, which was confirmed by a reduction of leukocyte acid alpha-glucosidase activity.

CONCLUSIONS

Nutritional factors may have accelerated the presentation of the lysosomal storage disorder. This is the first reported case of dysphagia caused by esophageal motor weakness in acid maltase deficiency.

Pro-inflammatory cytokines and the pathogenesis of Gaucher's disease: increased release of interleukin-6 and interleukin-10

Gaucher's disease is characterized by hepatosplenomegaly, bone-marrow infiltration, osteonecrosis and bone thinning, associated with the presence of pathological macrophages that contain undegraded glycosphingolipids. To investigate the possible role of cytokines in the systemic and local manifestations of established Gaucher's disease, interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF alpha) and interleukin-10 (IL-10) were measured in freshly-separated serum. Samples from eight male and 14 female patients with type 1 Gaucher's disease were compared with sera from 22 healthy age- and sex-matched controls. Concentrations of IL-6 and IL-10 were significantly elevated in sera from patients with Gaucher's disease (11.9 +/- 1.8 (SEM) pg/ml and 5.4 +/- 0.5 (SEM) pg/ml, respectively) compared with those of controls (4.1 +/- 0.9 (SEM) and 0.8 +/- 0.3 (SEM) pg/ml, p < 0.0001). No significant differences in concentrations of TNF alpha or IL-1 beta were identified. IL-6 has been implicated in the development of localized osteolysis in multiple myeloma and in the development of post-menopausal osteoporosis. High concentrations of IL-6 in the serum of patients with Gaucher's disease may thus reflect the development of the bone lesions commonly associated with this disorder. Since IL-6 and IL-10 are important regulators of lymphocyte growth and differentiation, and IL-6 concentrations were significantly raised in patients with oligo- or polyclonal increases in serum immunoglobulins, enhanced release of these cytokines from pathological macrophages provides a pathological link between Gaucher's disease and associated lympho-proliferative disorders.

Therapeutic delivery of proteins to macrophages: implications for treatment of Gaucher's disease

BACKGROUND

The primary defect in Gaucher's disease, a lysosomal disorder affecting macrophages, is in the activity of glucocerebrosidase. Treatment with exogenous enzyme (modified to increase its affinity for macrophage glycoprotein receptors) aims to restore this activity. However, the fate of the exogenous enzyme in vivo is unknown. We used radiolabelled enzyme to assess macrophage receptor activity for mannosylated ligands in vivo.

METHODS

We examined the uptake and tissue distribution of radiolabelled enzyme molecules by gamma scintigraphy after bolus injection of iodine-123-labelled recombinant or placental enzyme (imiglucerase and alglucerase, respectively) in eight patients with type 1 Gaucher's disease, and in one healthy individual. The metabolism of the tracer enzyme was followed by scintigraphy and by analysis of blood, urine, and faeces.

RESULTS

The tracer enzyme was rapidly cleared from blood (half-life 4.7 min [SD 1.0]). Concomitantly, there was avid uptake by the liver (about 30% of the injected dose), the spleen (about 15%), and the bone marrow. 40-55% of the tracer was cleared rapidly from the viscera (half-life 1-2 h) and 45-60% was cleared slowly (half-life 34-42 h). The half-life in the bone marrow was 14.1 h. Infusion of alglucerase at dose of 5 U/kg bodyweight normalised acid beta-glucosidase activity of splenic Gaucher's cells in vivo. When the enzyme was administered at a seven-fold higher dose (35 U/kg over 1 h), the receptor-mediated uptake in vivo was saturated, as shown by the increase in blood-clearance half-life of tracer enzyme from 4.5 min to 12 min.

INTERPRETATION

Avid and saturable uptake of modified glucocerebrosidase was found, which indicates high-affinity targeting to the macrophage system in vivo. The rate of enzyme turnover suggests a rational basis for use of this therapy in treatment of Gaucher's disease.

Neonatal screening for hereditary fructose intolerance: frequency of the most common mutant aldolase B allele (A149P) in the British population

Hereditary fructose intolerance (HFI) causes severe and sometimes fatal metabolic disturbances in infants and children but responds to dietary treatment. To determine the practicability of screening newborn infants for HFI, we have investigated the frequency of the most common and widespread mutant allele of aldolase B, A149P, in the neonatal population. The polymerase chain reaction was used to amplify aldolase B exon 5 genomic sequences in DNA present in dried blood specimens preserved on Guthrie cards. The A149P mutation was identified by discriminatory hybridisation to allele specific oligonucleotides and confirmed independently by digestion with the restriction endonuclease BsaHI. Twenty-seven A149P heterozygotes were identified by the molecular analysis of aldolase B genes in blood samples obtained from a random cohort of 2050 subjects born in 1994 and 1995, 1.32 +/- 0.49% (95% confidence level). Although no A149P homozygotes were identified, the data allow the frequency of 1 in 23,000 homozygotes for this allele to be predicted. Our findings have implications for establishing an interventional mass screening programme to identify newborn infants with HFI in the UK.

Mice lacking tartrate-resistant acid phosphatase (Acp 5) have disrupted endochondral ossification and mild osteopetrosis

Mature osteoclasts specifically express the purple, band 5 isozyme (Acp 5) of tartrate-resistant acid phosphatase, a binuclear metalloenzyme that can generate reactive oxygen species. The function of Acp 5 was investigated by targeted disruption of the gene in mice. Animals homozygous for the null Acp 5 allele had progressive foreshortening and deformity of the long bones and axial skeleton but apparently normal tooth eruption and skull plate development, indicating a role for Acp 5 in endochondral ossification. Histomorphometry and mineralization density analysis of backscattered electron imaging revealed widened and disorganized epiphyseal growth plates with delayed mineralization of cartilage in 6- to 8-week-old mutant mice. The membrane bones of the skull showed increased density at all ages examined, indicating defective osteoclastic bone turnover. Increased mineralization density was observed in the long bones of older animals which showed modelling deformities at their extremities: heterozygotes and homozygous Acp 5 mutant mice had tissue that was more mineralized and occupied a greater proportion of the bone in all regions. Thus the findings reflect a mild osteopetrosis due to an intrinsic defect of osteoclastic modelling activity that was confirmed in the resorption pit assay in vitro. We conclude that this bifunctional metalloprotein of the osteoclast is required for normal mineralization of cartilage in developing bones; it also maintains integrity and turnover of the adult skeleton by a critical contribution to bone matrix resorption.

Generation and characterization of monoclonal antibodies to human type-5 tartrate-resistant acid phosphatase: development of a specific immunoassay of the isoenzyme in serum

We have characterized four monoclonal antibodies (mAbs) to the purple ("tartrate-resistant," band 5) acid phosphatase of the human osteoclast (TRAP) and used these to develop a specific serum immunoassay. All four mAbs are of high affinity (Ka = 1-5 x 10(8) L/mol) with a very fast Kassoc (0.2-2.0 x 10(5) L mol-1 s-1) and a moderate Kdissoc (1-3 x 10(-3) s). Two of the mAbs were selected to develop a time-resolved fluorescence immunoassay to measure serum concentrations of TRAP. The mean serum immunoreactive TRAP in a group of healthy premenopausal women and men was 3.7 +/- 1.8 micrograms/L (mean +/- SD) and 3.5 +/- 1.6 micrograms/L, respectively. Significantly higher concentrations of TRAP were found in postmenopausal women (6.3 +/- 2.3 micrograms/L) and in eight patients with Gaucher disease (19.3 +/- 4.7 micrograms/L). Further studies are required to investigate the value of serum TRAP as a marker of bone resorption.

Generation and characterization of monoclonal antibodies to human type-5 tartrate-resistant acid phosphatase: development of a specific immunoassay of the isoenzyme in serum

We have characterized four monoclonal antibodies (mAbs) to the purple ("tartrate-resistant," band 5) acid phosphatase of the human osteoclast (TRAP) and used these to develop a specific serum immunoassay. All four mAbs are of high affinity (Ka = 1-5 x 10(8) L/mol) with a very fast Kassoc (0.2-2.0 x 10(5) L mol-1 s-1) and a moderate Kdissoc (1-3 x 10(-3) s). Two of the mAbs were selected to develop a time-resolved fluorescence immunoassay to measure serum concentrations of TRAP. The mean serum immunoreactive TRAP in a group of healthy premenopausal women and men was 3.7 +/- 1.8 micrograms/L (mean +/- SD) and 3.5 +/- 1.6 micrograms/L, respectively. Significantly higher concentrations of TRAP were found in postmenopausal women (6.3 +/- 2.3 micrograms/L) and in eight patients with Gaucher disease (19.3 +/- 4.7 micrograms/L). Further studies are required to investigate the value of serum TRAP as a marker of bone resorption.

Autosomal recessive erythropoietic protoporphyria: a syndrome of severe photosensitivity and liver failure

Erythropoietic protoporphyria is caused by inherited deficiency of the haem synthetic enzyme ferrochelatase, and is characterized by lifelong photosensitivity. About 5% of patients also develop rapidly progressive liver failure. Inheritance is considered to be autosomal dominant, with transmission of a single ferrochelatase defect from one parent. We describe a family in which two siblings with protoporphyria suffered from severe photosensitivity and developed hepatic failure requiring liver transplantation. Their asymptomatic parents were heterozygous for distinct ferrochelatase gene mutations (exon 10 donor site a(+3)-->g and 1088T-->G). Both mutations disrupt splicing of the transcript and cause partial deficiency of ferrochelatase. The affected offspring were compound heterozygotes for these mutations. These patients suffered from an autosomal recessive form of protoporphyria characterized by severe photosensitivity and cholestatic liver disease in adolescence. We postulate that hepatic failure in erythropoietic protoporphyria may in some cases represent an autosomal recessive type of ferrochelatase deficiency distinct from the purely dermatological disorder. Studies of disease inheritance in families affected by protoporphyria may help identify those predisposed to develop severe liver complications, a distinction not currently possible.

Diverse mutations in the aldolase B gene that underlie the prevalence of hereditary fructose intolerance

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Anti-interleukin-4 treatment diminishes secretion of Th2 cytokines and inhibits hepatic fibrosis in murine schistosomiasis japonica

Anti-interleukin-4 (IL-4) treatment of Schistosoma japonicum-infected mice markedly inhibited in vitro secretion of the Th2 cytokines IL-4 and IL-5 from antigen-stimulated spleen cells, but enhanced the secretion of the Th1 cytokine IFN-gamma. IL-2 secretion was unaffected. Hepatic fibrosis was markedly diminished in anti-IL-4-treated-mice at ten weeks of infection while granulomas around S. japonicum eggs in the livers were slightly-to-moderately increased in size. The number of eggs per worm pair in the tissues and feces did not differ significantly in treated and untreated mice. These findings suggest that Th2 cytokine responses are important in the genesis of schistosomal hepatic fibrosis.

Anti-IL-4 treatment of Schistosoma mansoni-infected mice inhibits development of T cells and non-B, non-T cells expressing Th2 cytokines while decreasing egg-induced hepatic fibrosis

Increasing evidence suggests that schistosome egg granulomas are primarily Th2 cellular reactions. Mice infected with Schistosoma mansoni were treated with a neutralizing mAb against IL-4 to evaluate the role of this cytokine in the generation of parasite egg-induced cell-mediated responses and hepatic pathology. Animals treated with anti-IL-4 before egg deposition showed decreased IL-4, IL-5, and IL-10 production in response to in vitro antigenic stimulations and decreased IL-5 and IL-13 mRNA levels in the liver. As observed previously, non-B, non-T cells were a major source of IL-4 in infected mice treated with control mAb, and the diminished IL-4 response in anti-IL-4-treated animals was shown to be caused at least in part by a reduction in the number of these cells, as well as by decreased secretion of IL-4 per cell. In contrast, production of the Th1 cytokines IL-2 and IFN-gamma was elevated in anti-IL-4-treated infected mice in vitro, and the corresponding mRNAs in the liver were increased. Anti-IL-4 treatment did not consistently reduce the size of hepatic granulomas around S. mansoni eggs, but markedly inhibited granuloma formation in the lungs of the same animals after i.v. egg injection. Nevertheless, anti-IL-4-treated infected mice showed consistent and marked reductions in hepatic collagen deposition. These findings indicate that IL-4 plays a major role in the development of the Th2 response in S. mansoni-infected mice and contributes to the pathogenesis of hepatic fibrosis.

Anti-IL-4 treatment of Schistosoma mansoni-infected mice inhibits development of T cells and non-B, non-T cells expressing Th2 cytokines while decreasing egg-induced hepatic fibrosis

Increasing evidence suggests that schistosome egg granulomas are primarily Th2 cellular reactions. Mice infected with Schistosoma mansoni were treated with a neutralizing mAb against IL-4 to evaluate the role of this cytokine in the generation of parasite egg-induced cell-mediated responses and hepatic pathology. Animals treated with anti-IL-4 before egg deposition showed decreased IL-4, IL-5, and IL-10 production in response to in vitro antigenic stimulations and decreased IL-5 and IL-13 mRNA levels in the liver. As observed previously, non-B, non-T cells were a major source of IL-4 in infected mice treated with control mAb, and the diminished IL-4 response in anti-IL-4-treated animals was shown to be caused at least in part by a reduction in the number of these cells, as well as by decreased secretion of IL-4 per cell. In contrast, production of the Th1 cytokines IL-2 and IFN-gamma was elevated in anti-IL-4-treated infected mice in vitro, and the corresponding mRNAs in the liver were increased. Anti-IL-4 treatment did not consistently reduce the size of hepatic granulomas around S. mansoni eggs, but markedly inhibited granuloma formation in the lungs of the same animals after i.v. egg injection. Nevertheless, anti-IL-4-treated infected mice showed consistent and marked reductions in hepatic collagen deposition. These findings indicate that IL-4 plays a major role in the development of the Th2 response in S. mansoni-infected mice and contributes to the pathogenesis of hepatic fibrosis.

Recessive inheritance of erythropoietic protoporphyria with liver failure

Erythropoietic protoporphyria is characterised by skin photosensitivity and deficiency of ferrochelatase; fatal liver disease occurs rarely. Transmission is considered to be dominant with incomplete penetrance. We investigated a family in which two siblings with erythropoietic protoporphyria developed hepatic failure that required transplantation. Their healthy parents had partial enzyme deficiency and were each heterozygous for a distinct mutation in a ferrochelatase gene. Both offspring were compound heterozygotes with ferrochelatase deficiency. Recessive transmission of protoporphyria predisposes to severe liver disease in this family. Patients with the recessive form of this disease may be at special risk of hepatic failure.

Null alleles of the aldolase B gene in patients with hereditary fructose intolerance

We report three new mutations in the gene for aldolase B that are associated with hereditary fructose intolerance (HFI). Two nonsense mutations create opal termination codons: R3op (C-->T, Arg3-->ter, exon 2) was found in homozygous form in four affected members of a large consanguineous Turkish pedigree and R59op (C-->T, Arg59-->ter, exon 3) was found on one allele in a woman of Austrian origin known to harbour one copy of the east European mutation, N334K (Asn334-->Lys). The third mutation occurred in a French HFI patient known to be heterozygous for the widespread mutation, A174D (Ala174-->Asp): a single mutation, G-->A, in the consensus acceptor site 3' of intron 6 was found on the remaining allele. These mutations are predicted to abrogate synthesis of functional protein and thus represent null alleles of aldolase B. The mutant alleles can be readily detected in the amplification refractory mutation system (ARMS) or (for R59op and 3' intron 6) by digestion of amplified genomic fragments with DdeI or A1wNI, respectively, to facilitate direct diagnosis of HFI by molecular analysis of aldolase B genes.

Molecular characterization of a ferrochelatase gene defect causing anomalous RNA splicing in erythropoietic protoporphyria

Erythropoietic protoporphyria is an inherited disorder caused by deficient activity of the enzyme ferrochelatase. We have examined the ferrochelatase gene in an 11-year-old female with protoporphyria and have found that she is heterozygous for a mutation at a conserved residue in the exon 3 donor splice site consensus sequence (T(+2)-->G). This is inherited from her father, who also has deficient ferrochelatase activity. As a consequence of the mutation, ferrochelatase transcripts are aberrantly spliced and give rise to mRNA molecules in which sequences corresponding to exon 3 are absent. This leads to the expression of a ferrochelatase protein lacking a central region of 40 amino acids.

Molecular analysis of functional and nonfunctional genes for human ferrochelatase: isolation and characterization of a FECH pseudogene and its sublocalization on chromosome 3

A pseudogene related to the functional gene (FECH) for the heme biosynthetic enzyme ferrochelatase (ferroheme-protolyase; EC 4.99.1.1.) was isolated from a human genomic library using a ferrochelatase cDNA hybridization probe. The pseudogene shows > 80% overall nucleotide sequence identity to the functional gene (including the 3' untranslated region and polyadenylation signals) but contains no intronic sequences in the region corresponding to the open reading frame of expressed ferrochelatase. Furthermore, the pseudogene sequence contains small deletions and insertions creating frameshifts and numerous termination codons, indicating that it does not encode a functional polypeptide. Northern blot analysis using pseudogene-specific probes failed to demonstrate transcripts in samples of human erythroid cell RNA in which ferrochelatase mRNA was readily detected. Southern blot experiments using restriction endonuclease-digested human genomic DNA probed either with ferrochelatase-specific cDNA fragments or pseudogene-specific genomic sequences confirmed the presence of distinct loci for the expressed and nonfunctional genes, respectively. Localization of the human ferrochelatase pseudogene to 3p22-p23 was determined by fluorescent metaphase chromosomal hybridization in situ using three genomic clones in lambda EMBL3 spanning a contiguous region of approximately 30 kb. This newly identified locus, distinct from the expressed FECH gene, on 18q22, is characteristic of a processed human pseudogene. The existence of the ferrochelatase pseudogene has practical implications for the molecular analysis of mutations responsible for erythropoietic protoporphyria in man.

Purple acid phosphatase of the human macrophage and osteoclast. Characterization, molecular properties, and crystallization of the recombinant di-iron-oxo protein secreted by baculovirus-infected insect cells

The purple phosphatases catalyze hydrolysis of phosphate esters (optimum pH approximately 5) and are resistant to inhibition by dextro-rotatory tartrate; their distinctive color is due to Fe(III)-phenolate charge-transfer transitions at their active site. Expression of human purple phosphatase, designated type 5 acid phosphatase, is restricted to osteoclasts and other activated cells of monohistiocytic lineage, but its biological rôle in relation to bone resorption and phagocytosis is unknown. To characterize this enzyme further, we have engineered the human type 5 acid phosphatase into a baculovirus vector expression system that enabled milligram quantities of purple protein to be purified from medium containing Sf9 host cells. The phosphatase cDNA was transcribed as a single RNA species of 1.5 kilobases as in human tissues. Tartrate-resistant acid phosphatase activity reacting with uteroferrin antisera appeared in the culture medium, from which up to 8 mg/liter was purified by two-step cation-exchange chromatography at pH 8.0. Two isoforms of approximately 36 kDa were identified by SDS-polyacrylamide electrophoresis and were converted to a single species of apparent molecular size 34 kDa upon treatment with N-glycosidase F, indicating secreted glycoforms of a single polypeptide. Mass spectroscopy showed that the mean molecular mass of the active, secreted glycoprotein was 35849 Da. The recombinant enzyme (specific activity, 190 mumol p-nitrophenol/min/mg at 37 degrees C) contained 2 iron atoms/molecule and formed purple, monoclinic crystals. Exposure to the ferric chelator, 1,2-dimethyl-3-hydroxypyrid-4-one, rapidly inactivated the enzyme, which was not inhibited by alpha, alpha'-bipyridyl, a ferrous chelator. That ferric iron is essential for enzymatic catalysis, was further indicated by the synergistic effects of the reductant, dithiothreitol, and bipyridyl on phosphatase activity. The recombinant purple phosphatase catalyzed the peroxidation of 5-aminophthalhydrazide (luminol), as evidenced by the induction of chemiluminescence; this reaction was inhibited by alpha, alpha'-bipyridyl at concentrations that did not inhibit phosphatase activity. The divalent iron moiety of human type 5 phosphatase may therefore participate in the generation of free radical species by fluid-phase reactions involving Fenton chemistry that are dissociated from its phosphatase function.

Aldolase B and fructose intolerance

Hereditary fructose intolerance is an autosomal recessive disorder that illustrates vividly the interplay between heredity and environment in the genesis of human nutritional disease. Genetically determined defects of an isozyme of fructose bisphosphate aldolase (aldolase B, which is specialized for the metabolic assimilation of dietary sugars) predispose to this widely distributed condition. Ingestion of fructose, sorbitol, or sucrose induces abdominal pain, vomiting, and metabolic disturbances--including low concentrations of blood glucose--that may prove fatal. The response to dietary exclusion is rapid and, when so treated, the disease is compatible with a normal life span. A noteworthy feature of the condition in individuals who survive the stormy period of weaning is the development of powerful aversions to fruit, nuts, and sweet-tasting foods and drinks. The incidence of dental caries is consequently much reduced.

The glucocerebrosidase locus in Gaucher's disease: molecular analysis of a lysosomal enzyme

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Hereditary ovalocytosis with compensated haemolysis

The clinical and laboratory phenotype of compensated haemolysis in a patient with hereditary ovalocytosis is reported. Clinical presentation was intermittent jaundice and abdominal pain due to pigment gall stones. Haematological analysis revealed an absolute reticulocytosis with an otherwise normal full blood count and biochemical evidence of haemolysis. Variable results were observed with blood grouping reagents. The patient's red cells were stomatocytic ovalocytic, rigid, resistant to malarial parasite invasion, defective in anion transport, and had the characteristic two linked mutations in the red cell band 3 gene.

Regression of hepatic lesions after treatment of Schistosoma mansoni or Schistosoma japonicum infection in mice: a comparative study

Experimental infections with Schistosoma mansoni and S. japonicum differ in several aspects and post-treatment resorption of fibrosis might be one of them. To investigate this point, mice infected with each of these schistosome species were treated with praziquantel and the evolution of hepatic lesions was sequentially followed for five months. Parasitologic data showing destruction of worms and eggs and biochemical findings of progressively decreased collagen concentration after cure indicated that the lesions caused by S. mansoni and S. japonicum involuted in a similar fashion following chemotherapy. The time sequence of the histologic changes indicative of decreasing inflammation and progressive matrix degradation and resorption was also similar in both cases.

Schistosoma japonicum-infected mice show reduced hepatic fibrosis and eosinophilia and selective inhibition of interleukin-5 secretion by CD4+ cells after treatment with anti-interleukin-2 antibodies

Schistosoma japonicum-infected mice were injected with antibodies to interleukin-2 (IL-2) and/or IL-2 receptor to clarify the role of IL-2 on the granulomatous reaction around schistosome eggs in the liver. Granulomas were of normal or slightly increased size in animals subjected to IL-2 blockade, but hepatic fibrosis was markedly decreased in treated animals 10 weeks after infection. Anti-IL-2 treatment significantly decreased the in vitro secretion of IL-5 by antigen-stimulated spleen cells, and peripheral eosinophilia and tissue eosinophilia were diminished. Secretion of IL-2, IL-4, and gamma interferon was unaffected. Our results indicate that IL-2 is not an essential determinant of granuloma size in S. japonicum-infected mice but that, as in Schistosoma mansoni infection, the development of hepatic fibrosis is critically dependent on IL-2 levels and granuloma size and hepatic fibrosis are differentially regulated.

The MB PhD programme. Training to be a clinician-scientist in the UK

Rapid changes in the universities and in the organisation of the National Health Service are altering the perception of opportunity for clinical scientists in training. Cambridge University has established an integrated programme that combines training in scientific research and clinical medicine leading to the MB, BChir, and PhD degrees. The need for this and other options in the development of careers for aspiring medical researchers is reviewed here.

Biology and pathology of Schistosoma mansoni and Schistosoma japonicum infections in several strains of nude mice

Schistosoma mansoni and S. japonicum infections in nude mice (nu/nu) were compared with infections in nu/+ heterozygotes or intact mice. Seven to 12 weeks after exposure to S. mansoni, the responses of Swiss NCR, C3H, BALB/c and C57B1/6 nude mice did not differ substantially. Nude mice of all these strains showed minute granulomas around eggs in the liver and minimal hepatic fibrosis. Microvesicular and necrotizing changes in hepatocytes were similar in all mouse strains, and S. mansoni infections were frequently lethal to nude, but not to intact mice between the seventh and ninth weeks of infection. Nude mice that survived the ninth week of infection generally lived until the 12th week. The number of eggs per mature worm pair in the tissues of S. mansoni-infected nude mice was similar to the number in intact mice, but nude mice passed fewer eggs in the feces. Nude mice that received serum from infected intact mice excreted eggs in the stool in numbers equivalent to intact mice, but continued to form minute granulomas around S. mansoni eggs. Reconstitution with fetal thymus or with splenocytes from normal or S. mansoni-infected mice partially or completely restored hepatic granuloma size, granuloma eosinophils, hepatic fibrosis, and excretion of eggs in the feces. In contrast to S. mansoni infection, S. japonicum infections in nude mice did not cause necrosis of hepatocytes or excessive mortality, and S. japonicum eggs were passed in the feces in numbers equivalent to those passed by infected intact mice.

DNA diagnosis of fatal fructose intolerance from archival tissue

Hereditary fructose intolerance is a recessively-transmitted disorder of metabolism caused by deficiency of aldolase B in the liver, intestine and kidney, that responds favourably to an exclusion diet. The occurrence of fatal hepatorenal failure in a 16-year-old girl, who had received infusions of fructose and sorbitol during minor surgery, led us to suspect that she had suffered from hereditary fructose intolerance. Molecular analysis of leucocyte DNA obtained from her brother who had had a long-standing aversion to fruit and sugar, showed two previously unknown mutations in the aldolase B gene. An initiation codon mutation, M-1T, was inherited from the father, whereas Y203X, inherited from the mother, is a nonsense mutation that replaces a tyrosine codon by the ochre termination signal. The only source of genomic DNA from the index case was a fixed fragment of necrotic liver that had been obtained by needle aspiration postmortem and was embedded in paraffin wax. Analysis of aldolase B genes in this sample by procedures based on the polymerase chain reaction (PCR) confirmed the presence of both mutations in the proposita, the diagnosis of hereditary fructose intolerance, and the cause of death.

Successful treatment of bone marrow failure in Gaucher's disease with low-dose modified glucocerebrosidase

We report the beneficial effects of enzyme replacement therapy with mannose-terminated human glucocerebrosidase ('Ceredase') in a patient suffering from transfusion-dependent bone marrow failure due to Gaucher's disease. Treatment with low-dose enzyme infusions, given twice weekly, rapidly reversed the haematopoietic failure and incapacitating skeletal disease. It appears likely that prior splenectomy favourably influenced the response to this therapy.

Genetic diagnosis of Gaucher's disease

The inherited disorder Gaucher's disease can be caused by various mutations in the glucocerebrosidase gene. Some mutations may be associated with greater severity, and there is a need for methods of gene analysis that would facilitate screening and diagnosis. We have studied the molecular basis of Gaucher's disease in twelve unrelated patients of diverse ethnic origin by means of the amplification refractory mutation system (ARMS). Primers for the polymerase chain reaction were designed to discriminate between mutant and wild-type alleles of glucocerebrosidase and to allow separation from products of the related pseudogene. The nucleotide 1226 mutation (asparagine 370----serine) and 84GG (an insertional frameshift mutation) were found exclusively in five patients of Ashkenazi Jewish descent (7 and 2 of the 10 disease alleles, respectively). Two point mutations, at nucleotides 1448 (leucine 444----proline) and 1504 (arginine 463----cysteine), were found in 4 and 3 alleles, respectively; they were associated with rapidly progressive disease and neurological involvement in non-Jewish patients. The ARMS procedure for direct detection of common mutations in glucocerebrosidase will facilitate genetic counselling and screening programmes for individuals at risk of Gaucher's disease.

Basis of unique red cell membrane properties in hereditary ovalocytosis

Hereditary ovalocytes from a Mauritian subject are extremely rigid, with a shear elastic modulus about three times that of normal cells, and have increased resistance to invasion by the malaria parasite Plasmodium falciparum in vitro. The genetic anomaly resides in band 3; the protein gives rise to chymotryptic fragments with reduced mobility in SDS/polyacrylamide gel electrophoresis, but this is a result of anomalous binding of SDS and not a higher molecular weight. Analysis of the band 3 gene reveals (1) a point mutation (Lys56----Glu), which also occurs in a common asymptomatic band 3 (Memphis) variant and governs the electrophoretic properties, and (2) a deletion of nine amino acid residues, including a proline residue, encompassing the interface between the membrane-associated and the N-terminal cytoplasmic domains. The interaction of the mutant band 3 with ankyrin appears unperturbed. The fraction of band 3 capable of undergoing translation diffusion in the membrane is greatly reduced in the ovalocytes. Cells containing the asymptomatic band 3 variant were normal with respect to all the properties that we have studied. Possible mechanisms by which a structural change in band 3 at the membrane interface could regulate rigidity are examined.