Biomedical subjects
Publications and source records attributed to M Poulter.
Following our previous report of an 144-bp insertion in the open reading frame of the prion protein (PrP) gene, we have now identified a larger, 216-bp, insertion in the gene. The insertion which is in frame encodes 9 extra octapeptide repeat sequences in addition to the 5 repeats normally present and represents the largest insertion so far detected in the PrP gene.
Genealogical and molecular studies were carried out in four families in which early onset dementia is inherited as an autosomal dominant. These studies indicated that the four families derive from four siblings whose parents were born in the late 18th century in South-East England. The disease was found to be closely linked to a 144 bp insertion within the open reading frame of the prion protein (PrP) gene with a maximum LOD score of 11.02 at zero recombination. Within the general population the PrP gene is polymorphic at codon 129 (allele frequency approximately 30% valine, 70% methionine). The insertion in this family is always within a methionine-129 allele. The age at death of affected individuals whose normal allele encoded methionine at codon 129 was significantly lower than those whose normal allele encoded valine. The clinical features which were very variable and the neuropathological findings, which sometimes included spongiform encephalopathy, but which often did not, are described fully in the accompanying article (Collinge et al., 1992).
A large family with autosomal dominant segregation of presenile dementia, and other neurological and behavioural features is described. At various times, family members have carried diagnoses of Alzheimer's disease, Huntington's disease, Parkinson's disease, myoclonic epilepsy, atypical dementia, Pick's disease, Creutzfeldt-Jakob disease and Gerstmann-Sträussler syndrome. Molecular genetic studies have enabled classification of this disease at the molecular level as one of the group of inherited prion diseases. Here we describe the phenotype of inherited prion disease (PrP 144 bp insertion).
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A number of mutations have been demonstrated in the open reading frame (ORF) of the prion protein (PrP) gene in patients with familial Creutzfeldt-Jakob disease or Gerstmann-Sträussler syndrome. On the basis of detecting an insertion in the ORF of the PrP gene in a patient originally suspected to be suffering from familial Alzheimer-type dementia, we screened 101 individuals with atypical dementias for the known PrP gene mutations. Insertions were found in five individuals, whereas none of the other reported mutations in the PrP gene was detected in the present study. One of the five insertions was larger than that described previously, suggesting that the individuals with these mutations are unlikely to be all lineally related and that insertions in the PrP gene may not be uncommon in prion diseases.
A susceptibility locus for schizophrenia in the 'pseudo-autosomal' region has been proposed on the basis of the reported excess of sex-chromosome aneuploidies (e.g. XXY and XXX) among patients with schizophrenia and the finding that schizophrenic sib-pairs are more often of the same than of the opposite sex. This hypothesis has been tested in 83 sibships with two or more siblings fulfilling Research Diagnostic Criteria for schizophrenia or schizoaffective disorder. Alleles at the pseudo-autosomal telomeric locus DXYS14, which is unlinked with sex, were analysed using the method of affected sib-pairs. Affected sibs shared alleles at DXYS14 more frequently than expected by random Mendelian assortment, supporting genetic linkage between DXYS14 and schizophrenia.
The identification of defects in the prion protein (PrP) gene in families with inherited Creutzfeldt-Jakob disease or Gerstmann-Straussler syndrome allows presymptomatic diagnosis or exclusion of these disorders in subjects at risk. After counseling, PrP gene analysis was performed in three such individuals: two from families with a 144-bp insert and one with a point mutation at codon 102 in the PrP gene. The presence of a PrP gene defect was confirmed in one and excluded in two. Despite the potential problems of using PrP gene analysis in genetic prediction - specifically, uncertainty about penetrance and, generally, problems of presymptomatic testing in any inherited late-onset neurodegenerative disorder - we conclude that it has a role to play in improved genetic counseling for families with inherited prion diseases.
Gerstmann-Sträussler syndrome (GSS) was diagnosed in a family with presenile dementia by prion protein gene analysis. Extensive histological examination of the brain of an affected individual from this family showed no characteristic features of GSS or Creutzfeldt-Jakob disease (CJD). Thus "spongiform encephalopathy" (GSS or CJD) cannot always be excluded on neuropathological grounds in an individual dying of a dementing condition, and the true prevalence of these diseases is likely to be underestimated. Screening by prion protein gene analysis will help to determine the full clinical and neuropathological phenotype in familial cases. This observation may be relevant to the assessment of possible transmission of bovine spongiform encephalopathy to man.
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In a pedigree with Creutzfeldt-Jakob disease we identified a 144-bp insertion in the open reading frame of the prion protein (PrP) gene. The insertion is in-frame and codes for 6 extra uninterrupted octapeptide repeats in addition to the 5 that are normally present in the N-terminal region of the protein. The possibility that this mutation may prove relevant to elucidating the mechanism of horizontal transmission of the spongiform encephalopathies is discussed.
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The polymerase chain reaction was used to screen DNA samples from 12 unrelated individuals with various familial dementias and ataxias for mutation in part of the prion protein (PrP) gene, an abnormality that occurs in individuals with the spongiform encephalopathies, Gerstmann-Sträussler syndrome (GSS) and Creutzfeldt-Jakob disease. 2 members of a family in whom GSS was not previously suspected had a 0.15 kb insertion of similar size to that found in another kindred with pathologically proven spongiform encephalopathy. GSS may be more common than is currently realised; PrP gene analysis is potentially useful for diagnosis and genetic counselling in familial dementias and ataxias.
Gerstmann-Sträussler syndrome is a rare familial neurodegenerative condition that is vertically transmitted, in an apparently autosomal dominant way. It can also be horizontally transmitted to non-human primates and rodents through intracerebral inoculation of brain homogenates from patients with the disease. The exact incidence of the syndrome is unknown but is estimated to be between one and ten per hundred million. Patients initially suffer from ataxia or dementia and deteriorate until they die, in one to ten years. Protease-resistant prion protein (PrP) and PrP-immunoreactive amyloid plaques with characteristic morphology accumulate in the brains of these patients. Current diagnostic criteria for Gerstmann-Sträussler syndrome incorporate clinical and neuropathological features, as animal transmission studies can be unreliable. PrP is implicated in the pathogenesis and transmission of the condition and in scrapie, an equivalent animal disease. It was discovered by enriching scrapie-infected hamster brain fractions for infectivity. Because there is compelling evidence that the scrapie isoform of PrP is a necessary component of the infectious particle, it seemed possible that the PrP gene on the short arm of human chromosome 20 in Gerstmann-Sträussler syndrome might be abnormal. We show here that PrP codon 102 is linked to the putative gene for the syndrome in two pedigrees, providing the best evidence to date that this familial condition is inherited despite also being infectious, and that substitution of leucine for proline at PrP codon 102 may lead to the development of Gerstmann-Sträussler syndrome.
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Serotonergic mechanisms have been investigated in postmortem brain samples from controls and suicide victims. The concentrations of 5-hydroxytryptamine (serotonin; 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in occipital cortex and hippocampus and the high-affinity binding of ligands to the 5-HT1, 5-HT2 and imipramine-binding sites was assessed in frontal cortex, occipital cortex and hippocampus. The only significant difference between the two groups was a modest increase in 5-HIAA levels in the hippocampus of suicide victims. There was no evidence to suggest that those suicide victims with a clinical history of depression represented a subgroup with altered metabolite levels or binding values. The storage conditions of the samples were not related to the metabolite levels or binding values. There was, however, a significant positive correlation between [3H]imipramine binding and age in some brain regions. The results do not provide any evidence of gross alterations in 5-HT mechanisms in suicide or depression.
Neurochemical indices of dopaminergic function were assessed in basal ganglia of post-mortem brains of control subjects and schizophrenic patients who had been rated in life for the presence of movement disorder and neuroleptic intake. In schizophrenics who had been treated chronically with doses of neuroleptics, concentrations of dopamine D2 receptors were significantly increased above controls, whereas dopamine D1 receptors and dopamine metabolism were unchanged. Increased D2 receptors were also observed in basal ganglia of drug-free patients. Concentrations of dopamine D1 and D2 receptors in schizophrenics with movement disorder. Moreover, no relationship was found between dopamine receptor levels and the severity of movement disorder. Concentrations of the dopamine metabolite homovanillic acid were increased in the putamen and nucleus accumbens in a small number of patients with movement disorder compared with controls or patients without movement disorder. No changes were observed in markers of cholinergic and GABA-containing neurones. The present findings are not consistent with a "dopamine receptor hypersensitivity" concept of movement disorder in schizophrenia.
Opioid receptor binding sites were assessed in membrane preparations of caudate nucleus from post-mortem brains of controls and of patients with schizophrenia. There was no difference between the two groups in the total specific binding of 3H-etorphine or in its 'mu' and ('delta + kappa') components. Similarly, the binding of 3H-naloxone did not differ between patients and controls. It is concluded that a previous report of reduced opioid receptors in caudate of schizophrenics is unlikely to prove a consistent finding and that the results of the present study offer no support to the claim that there is a general disturbance in opiate mechanisms in schizophrenia.