Novel presenilin 1 variant (P117A) causing Alzheimer's disease in the fourth decade of life

Genetics of dementia: insights from Latin America

Alzheimer’s disease (AD) and frontotemporal dementia (FTD) are neurodegenerative disorders that result in a significant burden to both patients and caregivers. By 2050, the number of people with dementia in Latin America will increase 4-fold. A deep understanding of the relevant genetic factors of AD and FTD is fundamental to tackle this reality through prevention. A review of different genetic variants that cause AD or FTD in Latin America was conducted. We searched Medline and PubMed databases using the keywords “Alzheimer’s disease,” “frontotemporal dementia,” “mutation,” “America,” and “Latin America,” besides specific Latin American countries. Forty-five items were chosen and analyzed. PSEN1 mutations are the commonest cause of genetic early-onset Alzheimer’s disease (EOAD), followed by PSEN2 and APP mutations. Genetic FTD can be mainly explained by GRN and MAPT mutations, as well as C9orf72 G4C2 repeat expansion. APOE ε4 can modify the prevalence and incidence of late-onset Alzheimer’s disease (LOAD), in addition to the cognitive performance in affected carriers.

Difficult case of a rare form of familial Alzheimer’s disease with PSEN1 P117L mutation

Less than 10% of Alzheimer’s disease (AD) cases are familial. Presenilin-1 (PSEN1) mutations are the most frequent aetiology and may be associated to atypical neurological manifestations. We report the case of a 27-year-old right-handed man, ensuing with mild cognitive impairment, motor discoordination and axial myoclonus after a parachute accident. At age 32 he was referred to our neurology clinic, presenting cognitive impairment, cerebellar syndrome, axial myoclonus and hypomimia, without other signs of parkinsonism. Because of absence of family history, he was worked up along the line of spinal ataxic disorders. Later, he developed pseudobulbar affect, cognitive deterioration, right upper limb paresis and spastic paraparesis. Subsequent investigation identified a PSEN1 P117L mutation and the diagnosis of autosomal dominant AD was made. This case illustrates the diagnostic challenge imposed by atypical presentation of de novo PSEN1 mutation, leading to unnecessary investigation. Genetic study might be essential for defining the diagnosis.

Genetic screening in two Iranian families with early-onset Alzheimer's disease identified a novel PSEN1 mutation

A subset of early-onset Alzheimer's disease is inherited as an autosomal-dominant trait and is associated with mutations in the genes encoding β-amyloid precursor protein, presenilin 1, or presenilin 2. In this study, we identified 2 PSEN1 mutations (1 novel and 1 known) in 2 unrelated Iranian families with autosomal-dominant Alzheimer's disease. The disease progressed rapidly with a mean age at onset of 33 and 42 years and an age at death ranging from 43 to 48 years.

The rare DAT coding variant Val559 perturbs DA neuron function, changes behavior, and alters in vivo responses to psychostimulants

Despite the critical role of the presynaptic dopamine (DA) transporter (DAT, SLC6A3) in DA clearance and psychostimulant responses, evidence that DAT dysfunction supports risk for mental illness is indirect. Recently, we identified a rare, nonsynonymous Slc6a3 variant that produces the DAT substitution Ala559Val in two male siblings who share a diagnosis of attention-deficit hyperactivity disorder (ADHD), with other studies identifying the variant in subjects with bipolar disorder (BPD) and autism spectrum disorder (ASD). Previously, using transfected cell studies, we observed that although DAT Val559 displays normal total and surface DAT protein levels, and normal DA recognition and uptake, the variant transporter exhibits anomalous DA efflux (ADE) and lacks capacity for amphetamine (AMPH)-stimulated DA release. To pursue the significance of these findings in vivo, we engineered DAT Val559 knock-in mice, and here we demonstrate in this model the presence of elevated extracellular DA levels, altered somatodendritic and presynaptic D2 DA receptor (D2R) function, a blunted ability of DA terminals to support depolarization and AMPH-evoked DA release, and disruptions in basal and psychostimulant-evoked locomotor behavior. Together, our studies demonstrate an in vivo functional impact of the DAT Val559 variant, providing support for the ability of DAT dysfunction to impact risk for mental illness.