Role of MAPT mutations and haplotype in frontotemporal lobar degeneration in Northern Finland

<p>Abstract</p> <p>Background</p> <p>Frontotemporal lobar degeneration (FTLD) consists of a clinically and neuropathologically heterogeneous group of syndromes affecting the frontal and temporal lobes of the brain. Mutations in microtubule-associated protein tau (<it>MAPT</it>), progranulin (<it>PGRN</it>) and charged multi-vesicular body protein 2B (<it>CHMP2B</it>) are associated with familial forms of the disease. The prevalence of these mutations varies between populations. The H1 haplotype of <it>MAPT </it>has been found to be closely associated with tauopathies and with sporadic FTLD. Our aim was to investigate <it>MAPT </it>mutations and haplotype frequencies in a clinical series of patients with FTLD in Northern Finland.</p> <p>Methods</p> <p><it>MAPT </it>exons 1, 2 and 9–13 were sequenced in 59 patients with FTLD, and <it>MAPT </it>haplotypes were analysed in these patients, 122 patients with early onset Alzheimer's disease (eoAD) and 198 healthy controls.</p> <p>Results</p> <p>No pathogenic mutations were found. The H2 allele frequency was 11.0% (<it>P </it>= 0.028) in the FTLD patients, 9.8% (<it>P </it>= 0.029) in the eoAD patients and 5.3% in the controls. The H2 allele was especially clustered in patients with a positive family history (<it>P </it>= 0.011) but did not lower the age at onset of the disease. The ApoE4 allele frequency was significantly increased in the patients with eoAD and in those with FTLD.</p> <p>Conclusion</p> <p>We conclude that although pathogenic <it>MAPT </it>mutations are rare in Northern Finland, the <it>MAPT </it>H2 allele may be associated with increased risks of FTLD and eoAD in the Finnish population.</p

Frontotemporal lobar degeneration in Finland:molecular genetics and clinical aspects

Abstract Frontotemporal lobar degeneration (FTLD) is the second most common neurodegenerative disease leading to early-onset dementia (&#60;&#160;65 years), next to Alzheimer’s disease. FTLD is substantially a genetic disorder with up to 50% of cases having a positive family history. Mutations in the genes microtubule-associated protein tau (MAPT) and progranulin (PGRN) account for about 10–20% of all cases of FTLD. Hexanucleotide repeat expansion mutation within the gene C9ORF72 has recently been identified as the major cause of FTLD, FTLD with amyotrophic lateral sclerosis (ALS) and pure ALS. During this study, hexanucleotide repeat expansion within the C9ORF72 gene was shown to explain nearly 50% of familial and 30% of all FTLD cases in the Finnish population. Otherwise, the genetic background of Finnish FTLD is largely unknown. The object of the present work was to disentangle the genetic aetiology of FTLD in the Finnish population. We studied a cohort of patients with a clinical diagnosis of FTLD from the province of Northern Ostrobothnia, Finland. Sequencing analysis of the genes MAPT, charged multi-vesicular body protein 2B (CHMP2B) and TAR DNA binding protein (TARDBP) were performed and the MAPT haplotypes were analysed. Correlations between genotype and phenotype were studied in patients with C9ORF72 repeat expansion mutation. C9ORF72 expansion mutation explained nearly 30% of cases of FTLD in our cohort. Concomitant ALS and positive family history of the disease increased the possibility of carrying expanded C9ORF72. The clinical phenotype of C9ORF72 expansion carriers varied at presentation: both behavioural and language variants were detected with or without ALS. The behavioural presentations included prominent psychotic features, although psychiatric presentations were not overrepresented in expansion carriers. No pathogenic mutations were identified in the MAPT, CHMP2B and TARDBP genes in our series of FTLD patients. The H2 MAPT haplotype was associated with FTLD in the series. Our findings emphasise the importance of C9ORF72 expansion mutation in FTLD. While mutations in MAPT and PGRN cause a significant proportion of cases of FTLD worldwide, they seem to be rare causes of FTLD in the Finnish population. Besides being infrequent in other populations, mutations in CHMP2B and TARDBP are rare causes of FTLD in the Finnish population as well. Our findings have clinical implications for recognising phenotypic features characteristic of expanded C9ORF72 as well as for genetic counselling of Finnish patients with FTLD. Even though a considerable proportion of our cases of familial FTLD is caused by the C9ORF72 expansion, over 50&#160;% of our familial cases are without a molecular genetic diagnosis, suggesting that there are other unidentified causal genes to be found.Tiivistelmä Otsa-ohimolohkorappeumat on toiseksi yleisin työikäisten dementiaa aiheuttava etenevä aivojen rappeumasairaus. Toisinaan otsa-ohimolohkorappeumat esiintyvät yhdessä liikehermorappeuman, amyotrofisen lateraaliskleroosin (ALS), kanssa. Perinnöllisillä tekijöillä on todennäköisesti keskeinen merkitys taudin taustalla. Mutaatiot microtubule-associated protein tau (MAPT)- ja progranulin (PGRN) geeneissä aiheuttavat yhteensä 10–20&#160;% otsa-ohimolohkorappeumista maailmalla. C9ORF72-geenissä sijaitsevan toistojaksomonistuman on vastikään todettu olevan yleisin otsa-ohimolohkorappeumia ja ALS:a aiheuttava mutaatio. Mutaatio on erityisen yleinen suomalaisessa väestössä selittäen lähes 50&#160;% suvuittaisista ja 30&#160;% kaikista otsa-ohimolohkorappeumista. Oireyhtymän perinnöllisyys on muutoin huonosti tunnettu suomalaisessa väestössä. Tutkimuksen tavoitteena oli selvittää otsa-ohimolohkorappeumien geneettisiä syitä aineistossa, joka koostui vuosina 1999–2010 Oulun yliopistollisessa sairaalassa tutkituista potilaista. Tutkimuksessa selvitettiin MAPT-, charged multi-vesicular body protein 2B (CHMP2B)- ja TAR DNA-binding protein (TARDBP) geenien mutaatioiden esiintyvyyttä ja määritettiin MAPT-geenin haplotyypit. Lisäksi tutkittiin taudin kliinisiä erityispiirteitä C9ORF72-mutaation kantajilla. C9ORF72-mutaatio selitti lähes 30&#160;% otsa-ohimolohkorappeumista aineistossamme. Tutkimuksessa havaittiin, että suvuittain esiintyvä tautimuoto ja ALS yhdistyneenä otsa-ohimolohkorappeumaan liittyivät merkittävästi C9ORF72-mutaatioon. Monistuman kantajien fenotyyppi oli moninainen – ensioireina oli sekä käytösongelmia että kielellisiä vaikeuksia. Vaikka C9ORF72-mutaation kantajilla on kuvattu runsaasti psykoottisia oireita, psykoottiset oireet eivät olleet selvästi yliedustettuna mutaation kantajilla aineistossamme. Tutkimuksessa ei löydetty tautia aiheuttavia mutaatioita MAPT-, CHMP2B- tai TARDBP-geeneistä. Havaitsimme kuitenkin tilastollisesti merkittävän yhteyden MAPT-geenin H2-haplotyypin ja otsa-ohimolohkorappeumien välillä. Tuloksemme antavat uutta tietoa C9ORF72-mutaation kantajien kliinisistä erityispiirteistä. MAPT-geenin mutaatioiden merkitys otsa-ohimolohkorappeumien synnyssä ei näyttäisi olevan suomalaisessa väestössä niin merkittävä kuin muissa väestöissä. CHMP2B- ja TARDBP-mutaatiot ovat harvinainen oireyhtymän syy myös suomalaisessa väestössä. Tuloksiamme voidaan hyödyntää suomalaisten otsa-ohimolohkorappeumapotilaiden perinnöllisessä neuvonnassa. Huomattavista edistysaskelista huolimatta yli puolet suvuittain esiintyvistä tautitapauksistamme on vailla geneettistä diagnoosia, mikä antaa aihetta jatkotutkimuksille

Clinical Characteristics of C9ORF72-Linked Frontotemporal Lobar Degeneration

Background: The most common genetic cause of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) has been linked to a hexanucleotide repeat expansion in the C9ORF72 gene. The frequency of the C9ORF72 expansion in Finland is among the highest in the world. Methods: We assessed 73 Finnish patients with FTLD in order to examine the clinical characteristics associated with the expanded C9ORF72. Demographic and clinical features were evaluated. As a potential disease modifier, the apolipoprotein E (APOE) genotype was also assessed. Neuropathological analysis was available on 2 expansion carriers and 1 non-carrier. Results: The C9ORF72 expansion was present in 20 of 70 (29%) probands. Significant associations with the C9ORF72 expansion were observed for concomitant ALS and positive family history of dementia or ALS. Psychoses were detected in both carriers and non-carriers (21 vs. 10%, p = 0.25). The APOE ε4 allele did not cluster among expansion carriers. Numerous p62-positive neuronal inclusions were detected in the cerebellar cortex of the 2 expansion carriers. Conclusion: In line with the suggested C9ORF72 core phenotype, we also detected a high frequency of neuropsychiatric symptoms; however, these symptoms seem not be specific to C9ORF72-associated FTLD. FTLD should be considered in cases of middle-age-onset psychosis

A hexanucleotide repeat expansion in C9ORF72 is the cause of chromosome 9p21-linked ALS-FTD

The chromosome 9p21 amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD) locus contains one of the last major unidentified autosomal-dominant genes underlying these common neurodegenerative diseases. We have previously shown that a founder haplotype, covering the MOBKL2b, IFNK, and C9ORF72 genes, is present in the majority of cases linked to this region. Here we show that there is a large hexanucleotide (GGGGCC) repeat expansion in the first intron of C9ORF72 on the affected haplotype. This repeat expansion segregates perfectly with disease in the Finnish population, underlying 46.0% of familial ALS and 21.1% of sporadic ALS in that population. Taken together with the D90A SOD1 mutation, 87% of familial ALS in Finland is now explained by a simple monogenic cause. The repeat expansion is also present in one-third of familial ALS cases of outbred European descent, making it the most common genetic cause of these fatal neurodegenerative diseases identified to date