The benefits of a Neurogenetics clinic in an adult Academic Teaching Hospital.

Genetics is the backbone of Neurology, where a number of disorders have a genetic aetiology and are complex, requiring a dedicated Neurogenetics clinic. Genetics in the Republic of Ireland is under-resourced, with the lowest number of consultants per million of population in Europe. In November 2014, we established the monthly adult Neurogenetics clinic in Ireland, staffed by 2 consultants and 2 registrars from each speciality. We see patients with complex rare neurological conditions that may potentially have an underlying genetic basis, in the presence or absence of a family history. We performed a retrospective cohort analysis, reviewing symptoms and work-up data. Twenty-seven patients attended a pilot clinic over 12 months. Conditions encountered included Parkin-related PD, leucodystrophy, ataxia, fronto-temporal lobar degeneration, spinocerebellar ataxia type 6 (SCA6) and ataxia-telangiectasia. Identification of pathogenic mutations directed screening, treatment and facilitated onward genetic counselling (n = 10, 33%). A number of novel mutations were identified in MAPT gene ("missing tau mutation" McCarthy et al., Brain, 2015), SLCA1 gene and GRN (progranulin). Phenotypic features not previously reported were seen; e.g. writer's cramp in SCA6; paroxysmal myoclonus in the glucose transporter protein type 1 (GLUT1) deficiency. Breast cancer screening for ATM mutations carriers and referral to international experts in two undiagnosed patients were arranged. The establishment of a Neurogenetics clinic has addressed a gap in service and allowed identification of rare and atypical diagnoses.

Genetics of Frontotemporal Dementia.

Frontotemporal dementia (FTD) is the second most common cause of dementia following Alzheimer's disease (AD). Between 20 and 50% of cases are familial. Mutations in MAPT, GRN and C9orf72 are found in 60% of familial FTD cases. C9orf72 mutations are the most common and account for 25%. Rarer mutations (<5%) occur in other genes such as VPC, CHMP2B, TARDP, FUS, ITM2B, TBK1 and TBP. The diagnosis is often challenging due to symptom overlap with AD and other conditions. We review the genetics, clinical presentations, neuroimaging, neuropathology, animal studies and therapeutic trials in FTD. We describe clinical scenarios including the original family with the tau stem loop mutation (+14) and also the recently discovered 'missing tau' mutation +15 that 'closed the loop' in 2015.

Closing the tau loop: the missing tau mutation.

Frontotemporal lobar degeneration comprises a group of disorders characterized by behavioural, executive, language impairment and sometimes features of parkinsonism and motor neuron disease. In 1994 we described an Irish-American family with frontotemporal dementia linked to chromosome 17 associated with extensive tau pathology. We named this disinhibition-dementia-parkinsonism-amyotrophy complex. We subsequently identified mutations in the MAPT gene. Eleven MAPT gene splice site stem loop mutations were identified over time except for 5' splice site of exon 10. We recently identified another Irish family with autosomal dominant early amnesia and behavioural change or parkinsonism associated with the 'missing' +15 mutation at the intronic boundary of exon 10. We performed a clinical, neuropsychological and neuroimaging study on the proband and four siblings, including two affected siblings. We sequenced MAPT and performed segregation analysis. We looked for a biological effect of the tau variant by performing real-time polymerase chain reaction analysis of RNA extracted from human embryonic kidney cells transfected with exon trapping constructs. We found a c.915+15A>C exon 10/intron 10 stem loop mutation in all affected subjects but not in the unaffected. The c.915+15A>C variant caused a shift in tau splicing pattern to a predominantly exon 10+ pattern presumably resulting in predominant 4 repeat tau and little 3 repeat tau. This strongly suggests that the c.915+15A>C variant is a mutation and that it causes frontotemporal dementia linked to chromosome 17 in this pedigree by shifting tau transcription and translation to +4 repeat tau. Tau (MAPT) screening should be considered in families where amnesia or atypical parkinsonism coexists with behavioural disturbance early in the disease process. We describe the final missing stem loop tau mutation predicted 15 years ago. Mutations have now been identified at all predicted sites within the 'stem' when the stem-loop model was first proposed and no mutations have been found within the 'loop' region as expected. Therefore we 'close the tau loop' having 'opened the loop' 21 years ago.