Clinical Description
Most individuals with TARDBP-related amyotrophic lateral sclerosis-frontotemporal dementia (TARDBP-ALS-FTD) present with manifestations of amyotrophic lateral sclerosis (ALS) with upper and lower motor neuron disease (MND). Rarely, affected individuals present with pure (i.e., without other neurologic findings) frontotemporal dementia (FTD), a combination of ALS and FTD, or an atypical neurologic phenotype such as FTD with supranuclear palsy. Additional manifestations within the TARDBP-ALS-FTD phenotypic spectrum may appear during the disease course [Van Deerlin et al 2008, Yokoseki et al 2008] (see Table 2).
Of note, the clinical presentation of TARDBP-ALS-FTD may differ between and within families, causing an unpredictable pattern and age of onset of clinical manifestations.
ALS. The entire clinical spectrum of ALS (which includes abnormal muscle tone and tendon reflexes, fasciculations, muscle cramps, and gait disturbances) may be present. In one study, spinal onset (involving limb muscles) occurred in 62.5% of affected individuals, bulbar onset (including involvement of swallowing and speech) in 10%, and both bulbar and spinal onset in ~27% [Lattante et al 2013]. Some early cognitive impairment may be present even in individuals previously diagnosed with pure ALS [Gregory et al 2020].
FTD. The three main FTD clinical syndromes are behavioral variant FTD (bvFTD), semantic variant primary progressive aphasia (svPPA), and nonfluent/agrammatic variant primary progressive aphasia (nfvPPA). Studies of the rare instances of pure TARDBP-FTD show that affected individuals usually present with bvFTD with common behavioral features such as irritability, repetitive behavior, aggressiveness, and delusions that worsen progressively. These behavioral features can overlap with executive dysfunction, memory deficits, and changes in eating habits. Some individuals also manifest primary progressive aphasia (PPA) with language impairment resembling semantic dementia [Floris et al 2015].
Parkinsonism. Heterozygous TARDBP pathogenic variants have also been associated with parkinsonism. The manifestations include Parkinson-like weakness in the legs, overlapping with bvFTD, hallucinations, REM sleep behavior disorder, and mild cognitive impairment [Rayaprolu et al 2013].
Life expectancy for TARDBP-ALS is highly variable and mainly associated with an individual's clinical features. Overall disease duration averages three to five years from onset with a steady rate of decline.
For TARDBP-FTD, disease duration averages one to 16 years from onset, depending on the cohort [Floris et al 2015]. As expected, survival in FTD is markedly compromised when ALS manifestations become apparent [Geser et al 2009].