Table 4.

Genetic loci for common neurodegenerative disorders

	Gene	Locus	Clinical feature
Alzheimer's disease	PSEN1	14q24	Often resembles sporadic AD, however behavior presentation (agitation, depression, delusions and hallucinations) and motor symptoms (myoclonus, spastic paresis, parkinsonism, seizures are prominent in some cases.
	PSEN 2	1q31	Very rare (typically Volga German ancestry). Most commonly presents with amnesia. There is a high degree of phenotypic variation, 33% presenting with hallucinations and delusions, and 31% with seizures. Disease progression is slow, with rigidity, mutism and a bedridden state in the end stages.
	APP	21q21	Amnesic dementia associated with seizures commonly developing within 1-9 years after onset of dementia. Intracerebral hemorrhage is not uncommon.
Frontotemporal dementia	C9ORF72	9p21	Behavioral dementia (FTD) with amyotrophic lateral sclerosis
	MAPT	17q21	Behavioral dementia with Parkinsonism
	GRN	17q21	Behavioral dementia, with aphasia, apraxia, parkinsonism, dystonia
	VCP	9p13	Inclusion body myopathy with osteolytic bone disease (Paget's disease) and behavioral dementia.
	CHMP2B	3p11.2	Very rare, seen in Danish kindred; behavioral dementia, parkinsonism and progressive spastic paresis are often seen.
Huntington disease	Huntingtin	4p16	Choreoathetosis early in the course, with dystonia and akinetic rigidity in later stages. Neuropsychiatric features include executive dysfunction, depression, irritability, impulsivity, compulsive behaviors, anger and hostility, and depression.
Prion disease	PRNP	20p13	Accounts for 15% of human prion disease. Several types are recognized: fCJD, which in rare instances mimics amnesic AD, typically features myoclonic jerks, cerebellar signs, and akinetic mutism; FFI (progressive insomnia, dysautonomia, selective thalamic degeneration); GSS (a hereditary form with chronic cerebellar ataxia, pyramidal features, dysathria, oculodysmetria, and hyporeflexia, with dementia in later stages.

PSEN=Presenilin, APP=Amyloid precursor protein, C9ORF72 = Chromosome 9 open reading frame 72, MAPT=Microtubule-associated protein tau, GRN=Progranulin, VCP= Valosin-containing protein, CHMP2B=Chromatin-modifying protein 2B, PRNP=prion protein; f CJD=familial CJD, FFI=Familial fatal insomnia, GSS= Gerstmann-Straussler-Sheinker Syndrome