Ana B. Rodríguez-Martínez

A novel mutation (K317M) in the MAPT gene causes FTDP and motor neuron disease

Background: Frontotemporal dementia with parkinsonism is often linked to chromosome 17 and is related to mutations in the MAPT gene. In some families the genetic basis is still unknown. The authors report two pedigrees with FTDP-17 harboring a novel mutation (K317M) in exon 11 in the MAPT gene. Methods: The authors identified two apparently unrelated pedigrees with an autosomal dominant neurodegenerative condition. Thirteen patients were examined and eight autopsies were performed. Results: Mean age at onset was 48 years. Mean disease duration was 6 years. Dysarthria often heralded the disease. All cases had parkinsonism and pyramidalism and half of them had amyotrophy. Behavioral or personality changes were not a prominent feature. Cognitive decline appeared late in the evolution. Neuropathologically, a massive degeneration of the substantia nigra without Lewy bodies was a constant finding. A variable degree of frontotemporal atrophy was found. Corticospinal tract degeneration and anterior horn neuron loss were present in six of seven autopsies in which the spinal cord was examined. An extensive deposition of abnormal tau protein in a mixed pattern (neuronal, glial) was observed. Pick’s bodies were not seen. Biochemical analysis of tau revealed two bands of 64 and 68 kDa. Conclusion: Genetic analysis revealed the same novel mutation (K317M) in exon 11 of the MAPT gene in both pedigrees. A common haplotype between members of the two pedigrees suggests that they belong to the same family.

Phenotypic variability in familial prion diseases due to the D178N mutation

Background: Between January 1993 and December 2003, 19 patients with familial prion diseases due to the D178N mutation were referred to the regional epidemiological registry for spongiform encephalopathies in the Basque Country in Spain, a small community of some 2 100 000 inhabitants. Methods: Ten further patients belonging to the same pedigrees were retrospectively ascertained through neurological or neuropathological records. In four of the patients, the diagnosis was confirmed by analysing DNA obtained from paraffin blocks. In this article, we report on the clinical, genetic, and pathological features of the 23 patients carrying the D178N mutation confirmed by genetic molecular analysis. Haplotyping studies suggest a founder effect among Basque born families, explaining in part this unusually high incidence of the D178N mutation in a small community. Only two patients (8%) lack familial antecedents. Results: We have observed a phenotypic variability even among homozygous 129MM patients. Our findings challenge the currently accepted belief that MM homozygosity in codon 129 is always related to a fatal familial insomnia (FFI) phenotype. Indeed, seven out of 17 patients with a 129MM genotype in this series presented with a Creutzfeldt-Jakob disease (CJD) clinicopathological picture. Conclusions: The considerable clinical and pathological overlapping observed among homozygous 129MM patients favours the view that FFI and CJD178 are the extremes of a spectrum rather than two discrete and separate entities. Other genetic or environmental factors apart from the polymorphism in codon 129 may play a role in determining the phenotypic expression of the D178N mutation in the PRNP gene.

A Novel PRNP Y218N Mutation in Gerstmann-Straussler-Scheinker Disease With Neurofibrillary Degeneration

Gerstmann-Sträussler-Scheinker (GSS) disease is a prion disease associated with prion protein gene (PRNP) mutations. We report a novel PRNP mutation (Y218N) associated with GSS disease in a pathologically confirmed case and in two other affected family members. The clinical features of these cases met criteria for possible Alzheimer disease and possible frontotemporal dementia. Neuropathologic analysis revealed deposition of proteinase K-resistant prion protein (PrPres), widespread hyperphosphorylated tau pathology, abnormal accumulation of mitochondria in the vicinity of PrPres deposits, and expression of mutant ubiquitin (UBB+1) in neurofibrillary tangles and dystrophic neurites. Prion protein immunoblotting using 3F4 and 1E4 antibodies disclosed multiple bands ranging from approximately 20 kd to 80 kd and lower bands of 15 kd and approximately 10 kd, the latter only seen after a long incubation. These bands were partially resistant to proteinase K pretreatment. This pattern differs from those seen in Creutzfeldt-Jakob disease andresembles those reported in other GSS cases. The approximately 10kd band was recognized with anti-PrP C-terminus antibodies but not with anti-N terminus antibodies, suggesting PrP truncation at the N terminal. This new mutation extends the list of known mutations responsible for GSS disease and reinforces its clinical heterogeneity. Genetic examination of the PRNP gene should be included in the workup of patients with poorly classifiable dementia.

Somatic mosaicism in a case of apparently sporadic Creutzfeldt-Jakob disease carrying a de novo D178N mutation in the PRNP gene†‡

Transmissible spongiform encephalopathies (TSEs) are a group of rare fatal neurodegenerative disorders. Creutzfeldt‐Jakob disease (CJD) represents the most common form of TSE and can be classified into sporadic, genetic, iatrogenic and variant forms. Genetic cases are related to prion protein gene mutations but they only account for 10–20% of cases. Here we report an apparently sporadic CJD case with negative family history carrying a mutation at codon 178 of prion protein gene. This mutation is a de novo mutation as the parents of the case do not show it. Furthermore the presence of three different alleles (wild type 129M‐178D and 129V‐178D and mutated 129V‐178N), confirmed by different methods, indicates that this de novo mutation is a post‐zygotic mutation that produces somatic mosaicism. The proportion of mutated cells in peripheral blood cells and in brain tissue was similar and was estimated at approximately 97%, suggesting that the mutation occurred at an early stage of embryogenesis. Neuropathological examination disclosed spongiform change mainly involving the caudate and putamen, and the cerebral cortex, together with proteinase K‐resistant PrP globular deposits in the cerebrum and cerebellum. PrP typing was characterized by a lower band of 21 kDa. This is the first case of mosaicism described in prion diseases and illustrates a potential etiology for apparently sporadic neurodegenerative diseases. In light of this case, genetic counseling for inherited and sporadic forms of transmissible encephalopathies should take into account this possibility for genetic screening procedures.

5-Hydroxytryptamine 6 receptor (5-HT6) receptor and apolipoprotein E (ApoE) polymorphisms in patients with Alzheimer's disease in the Basque Country

Although there is considerable evidence implicating apolipoprotein E (ApoE) epsilon4 in the development of the Alzheimers disease (AD), additional factors are also known to be involved. Thus, an association has been described between C267T polymorphism of the 5-hydroxytryptamine 6 receptor (5-HT(6)) receptor gene and AD. This case-control study analyzes the ApoE and 5-HT(6) receptor polymorphisms in 173 cases and 102 age and sex matched controls from Araba and Bizkaia (The Basque Country, Spain). The analysis of ApoE showed the frequencies of epsilon4 allele to be significantly higher in AD patients (0.292) than in the controls (0.083). When 5-HT(6) receptor polymorphism was analyzed, a greater frequency of 267C allele was observed in AD patients than in controls, though the difference was not statistically significant. Likewise regarding ApoE epsilon4 status, no statistically significant difference was observed. In conclusion, the association of ApoE epsilon4 to AD in a sample of patients from the Basque Country is confirmed, though the association to C267T polymorphism of the 5-HT(6) receptor has not been observed.

Molecular evidence of founder effects of fatal familial insomnia through SNP haplotypes around the D178N mutation

This work presents a detailed investigation of the genomic region surrounding the PRNP gene in a sample of patients diagnosed with fatal familial insomnia (FFI) from several European countries, notably Spain. The main focus of the study was to explore the origins of the chromosomes carrying the D178N mutation by designing a single-nucleotide polymorphism (SNP) haplotype around the PRNP gene. Haplotypes were constructed by genotyping six SNPs (rs2756271, rs13040327, rs6037932, rs13045348, rs6116474, and rs6116475) in 25 FFI patients from all over Spain. To augment the geographical scope of our study, 13 further FFI cases from Germany (9) and Italy (4) were also examined. Genotyping of SNPs in conjunction with the analysis of genealogical data for a group of FFI patients revealed the existence of two distinct haplotypes potentially associated with the D178N mutation. Of them, GCATTA-M proved to be the common haplotype of Spanish patients, whereas ACATTA-M was typical of the German cases. It is interesting to note that both haplotypes were identified in the Italian samples: GCATTA-M in a family from the Tuscany region and ACATTA-M in a family from the Veneto region. Our findings suggest the occurrence of two independent D178N-129M mutational events in Europe, preserved and transmitted from one generation to the next until nowadays. Likewise, results based on the analysis of SNP data indicate that previous hypotheses postulating that the D178N mutation had independent origins for each family and that its global distribution was determined by recurrent mutational events must be regarded with caution.

Coexistence of protease sensitive and resistant prion protein in 129VV homozygous sporadic Creutzfeldt–Jakob disease: a case report

IntroductionThe coexistence of different molecular types of classical protease-resistant prion protein in the same individual have been described, however, the simultaneous finding of these with the recently described protease-sensitive variant or variably protease-sensitive prionopathy has, to the best of our knowledge, not yet been reported.Case presentationA 74-year-old Caucasian woman showed a sporadic Creutzfeldt–Jakob disease clinical phenotype with reactive depression, followed by cognitive impairment, akinetic-rigid Parkinsonism with pseudobulbar syndrome and gait impairment with motor apraxia, visuospatial disorientation, and evident frontal dysfunction features such as grasping, palmomental reflex and brisk perioral reflexes. She died at age 77.Neuropathological findings showed: spongiform change in the patient’s cerebral cortex, striatum, thalamus and molecular layer of the cerebellum with proteinase K-sensitive synaptic-like, dot-like or target-like prion protein deposition in the cortex, thalamus and striatum; proteinase K-resistant prion protein in the same regions; and elongated plaque-like proteinase K-resistant prion protein in the molecular layer of the cerebellum. Molecular analysis of prion protein after proteinase K digestion revealed decreased signal intensity in immunoblot, a ladder-like protein pattern, and a 71% reduction of PrPSc signal relative to non-digested material. Her cerebellum showed a 2A prion protein type largely resistant to proteinase K. Genotype of polymorphism at codon 129 was valine homozygous.ConclusionMolecular typing of prion protein along with clinical and neuropathological data revealed, to the best of our knowledge, the first case of the coexistence of different protease-sensitive prion proteins in the same patient in a rare case that did not fulfill the current clinical diagnostic criteria for either probable or possible sporadic Creutzfeldt–Jakob disease. This highlights the importance of molecular analyses of several brain regions in order to correctly diagnose rare and atypical prionopathies.

Atypical/Nor98 scrapie in the Basque Country: a case report of eight outbreaks

BackgroundSince 2002, an active surveillance program for transmissible spongiform encephalopathy in small ruminants in European Union countries allowed identification of a considerable number of atypical cases with similarities to the previously identified atypical scrapie cases termed Nor98.Case presentationHere we report molecular and neuropathological features of eight atypical/Nor98 scrapie cases detected between 2002 and 2009. Significant features of the affected sheep included: their relatively high ages (mean age 7.9 years, range between 4.3 and 12.8), their breed (all Latxa) and their PRNP genotypes (AFRQ/ALRQ, ALRR/ALRQ, AFRQ/AFRQ, AFRQ/AHQ, ALRQ/ALRH, ALRQ/ALRQ). All the sheep were confirmed as atypical scrapie by immunohistochemistry and immunoblotting. Two cases presented more PrP immunolabelling in cerebral cortex than in cerebellum.ConclusionsThis work indicates that atypical scrapie constitutes the most common small ruminant transmissible spongiform encephalopathy form in Latxa sheep in the Spanish Basque Country. Moreover, a new genotype (ALRQ/ALRH) was found associated to atypical scrapie.

Geographical analysis of the sporadic Creutzfeldt-Jakob disease distribution in the autonomous community of the Basque Country for the period 1995-2008.

Background: The Basque Country, in Spain, shows one of the highest sporadic Creutzfeldt-Jakob disease (sCJD) incidence rates in Europe. The purpose is to analyse a possible focus of unidentified external or environmental factors which could trigger the high incidence rates of sCJD in the Basque Country. Methods: We estimated the relative risk and the posterior relative risk distribution of sCJD cases for each town of the Basque Country and for the period 1995-2008. Results: 58 sCJD cases (44 definite and 14 probable) were selected for the geographic cluster analysis. In a first approach, referring to the relative risk, several municipalities in the Autonomous Community of the Basque Country showed more sCJD cases than expected. However, the posterior relative risk distribution showed no excess risk areas. Conclusions: Results from this survey indicate that a possible common source of development of the disease does not seem to be the reason of the high sCJD incidence.

Founder effect and recurrent mutational events in fatal familial insomnia

The origin and distribution of the D178N-129M mutationcausing fatal familial insomnia (FFI) are controversial.Some authors have found evidence of founder effects whileworking with genealogical data [1, 2], whereas otherspropose recurrent mutations based on STR data [3]. Arecent study on SNP haplotypes close to D178N [4]conflicts with findings derived from STRs and seems tosupport the notion of founder effect. However, a commentappearing in the present issue of Neurogenetics questionssuch results. The main points in Lee and Goldfarb’s critique[5] concern the use of G-test and the SNPs selected for theanalysis, concluding that we failed to provide conclusiveevidence that only two founder haplotypes are associatedwith all known European FFI cases.A thorough reading of the discussion section permits toperceive clearly that results are not presented as conclusiveevidence but rather pointing to a certain direction. Specif-ically, in the last paragraph, we consider several uncertain-ties that leave the debate as for the origin of FFI open [4]:(1) “the results presented herein do not exclude thepossibility that other less successful mutational eventsmight have occurred” and (2) “probably, the true numberof founding events will be greater than two (minimalnumber estimated from SNPs)”.As Lee and Goldfarb indicate, G-test was employed toevaluate whether there were significant differences infrequencies of SNP haplotypes between patients andcontrol group from Spain. Nevertheless, conclusion aboutminimal number of founder mutations does not stem fromG-test results but essentially from the meticulous examina-tion of haplotypic and genealogical data. The notion offounding events for the D178N mutation is not new. Basedon demographic records, Harder et al. [1] reconstructed alarge German FFI kindred and assigned nine patients tothree related pedigrees comprising more than 800 individ-uals, whose common ancestors were traced to the 17thCentury. Likewise, a recent survey demonstrated that 12FFI cases from the Basque Country belonged to threeprobably related pedigrees traced back to the 16th and 17thCenturies [2].The SNPs used to construct haplotypes were selectedaccording to proximity to the D178N mutation to avoidoverestimation of haplotypic diversity by recombination.Lee and Goldfarb consider “especially troubling” that thehaplotypes identified as cosegregating with D178N-129Mare common in the background population. This finding isneither surprising nor unexpected. Owing to elementaryprobabilistic reasons, the opportunity that a deleteriousmutation occurs in a chromosome harboring a relativelycommon haplotype in the population is conspicuously high.Last but not least, an evolutionary genetics consideration—bearing in mind that onset of FFI usually occurs after themutated individuals have had offspring, intensity of naturalselection against the autosomal dominant mutation shouldnot be too high, as deduced from published genealogies [1,2]. It seems, thereby, little probable that this neurodegen-erative disorder appears by recurrent mutations in different