ABSTRACT
Dominantly inherited GAA repeat expansions in FGF14 are a common cause of spinocerebellar ataxia (GAA-FGF14 ataxia; spinocerebellar ataxia 27B). Molecular confirmation of FGF14 GAA repeat expansions has thus far mostly relied on long-read sequencing, a technology that is not yet widely available in clinical laboratories. We developed and validated a strategy to detect FGF14 GAA repeat expansions using long-range PCR, bidirectional repeat-primed PCRs, and Sanger sequencing. We compared this strategy to targeted nanopore sequencing in a cohort of 22 French Canadian patients and next validated it in a cohort of 53 French index patients with unsolved ataxia. Method comparison showed that capillary electrophoresis of long-range PCR amplification products significantly underestimated expansion sizes compared to nanopore sequencing (slope, 0.87 [95% CI, 0.81 to 0.93]; intercept, 14.58 [95% CI, - 2.48 to 31.12]) and gel electrophoresis (slope, 0.84 [95% CI, 0.78 to 0.97]; intercept, 21.34 [95% CI, - 27.66 to 40.22]). The latter techniques yielded similar size estimates. Following calibration with internal controls, expansion size estimates were similar between capillary electrophoresis and nanopore sequencing (slope: 0.98 [95% CI, 0.92 to 1.04]; intercept: 10.62 [95% CI, - 7.49 to 27.71]), and gel electrophoresis (slope: 0.94 [95% CI, 0.88 to 1.09]; intercept: 18.81 [95% CI, - 41.93 to 39.15]). Diagnosis was accurately confirmed for all 22 French Canadian patients using this strategy. We also identified 9 French patients (9/53; 17%) and 2 of their relatives who carried an FGF14 (GAA)≥250 expansion. This novel strategy reliably detected and sized FGF14 GAA expansions, and compared favorably to long-read sequencing.
Subject(s)
Friedreich Ataxia , Spinocerebellar Ataxias , Humans , Canada , Friedreich Ataxia/genetics , Spinocerebellar Ataxias/genetics , Trinucleotide Repeat ExpansionSubject(s)
Dystonic Disorders , GTP Cyclohydrolase , Humans , Mutation , Heterozygote , GTP Cyclohydrolase/genetics , PedigreeABSTRACT
BACKGROUND: Epilepsy seems to be an important comorbidity in patients with early onset Alzheimer's disease (EOAD). Currently, seizures are still underestimated in this population. However, seizures may interact with AD evolution with possible acceleration of cognitive decline. OBJECTIVE: To better define the epileptic disorders observed in patients with EOAD. METHODS: All patients diagnosed as EOAD in our hospital between 2013 and 2019 with positive CSF biomarkers for AD were selected. The usual follow-up was extended with a 3-h EEG and a consultation with an epilepsy expert. Information on epilepsy and AD were collected and analyzed. RESULTS: Among the 25 included patients, 10 (40%) were classified as epileptic. Seizure types were tonic-clonic (25%), typical temporal seizures (25%), myoclonus (25%), focal extra-temporal seizures (8%), and other seizure types (17%). AD-E patients had a significant lower MMSE (15.3±8.4 AD-E versus 22.1±5.1 AD-NE, pâ=â0.036) and a lower autonomy (IADL 4.1±2.7 AD-E versus 6.4±1.9 AD-NE, pâ=â0.046) at AD diagnosis with comparable ages between AD-E and AD-NE. Epileptic patients seemed to present a faster cognitive decline ([ΔMMSE per year 1.7±1.3 AD-E versus 0.9±1.4 AD-NE; pâ=â0.09). All patients with severe cognitive impairment (MMSE ≤ 10) had an epileptic comorbidity. CONCLUSION: Epilepsy is a frequent comorbidity in EOAD patients, with a percentage of 40%in our study. This comorbidity may be associated with a severe form of EOAD. The role of epilepsy in the acceleration of cognitive decline and the positive impact of antiepileptic drugs on cognition need further research.
