The spectrum of GRN frontotemporal dementia (GRN-FTD) includes the behavioral variant (bvFTD), primary progressive aphasia (PPA; further subcategorized as progressive nonfluent aphasia [PNFA] and semantic dementia [SD]), and movement disorders with extrapyramidal features such as parkinsonism and corticobasal syndrome (CBS). A broad range of clinical features both within and between families is observed. The age of onset ranges from 35 to 87 years. Behavioral disturbances are the most common early feature, followed by progressive aphasia. Impairment in executive function manifests as loss of judgment and insight. In early stages, PPA often manifests as deficits in naming, word finding, or word comprehension. In late stages, affected individuals often become mute and lose their ability to communicate. Early findings of parkinsonism include rigidity, bradykinesia or akinesia (slowing or absence of movements), limb dystonia, apraxia (loss of ability to carry out learned purposeful movements), and disequilibrium. Late motor findings may include myoclonus, dysarthria, and dysphagia. Most affected individuals eventually lose the ability to walk. Disease duration is three to 12 years.

Congenital hypertryptophanemia, which is accompanied by hyperserotonemia, does not appear to have significant clinical consequences (Ferreira et al., 2017).

Neurodevelopmental disorder with early-onset parkinsonism and behavioral abnormalities (NEDPBA) is an autosomal recessive disorder characterized by delayed developmental milestones apparent in late infancy or early childhood, impaired intellectual development with learning difficulties, and behavioral abnormalities. Motor abnormalities, including parkinsonism and spasticity, usually develop in the third or fourth decades, although earlier onset has been reported. Some patients have seizures. There is inter- and intrafamilial variability (Kuipers et al., 2018; Al-Kasbi et al., 2021).