Table 3.

Inherited Conditions to Consider in the Differential Diagnosis of Spinocerebellar Ataxia Type 17 (SCA17)

DiffDx DisorderGene(s)MOIClinical Features of the DiffDx Disorder
Overlapping w/SCA17Distinguishing from SCA17
Hereditary cerebellar ataxia (See Hereditary Ataxia Overview.)ManyAD
AR
XL		Cerebellar ataxiaHereditary cerebellar ataxia assoc w/prominent cerebellar & long tract signs
DRPLA (dentatorubral-pallidoluysian atrophy) ATN1 ADProgressive ataxia & dementia; psychiatric disturbancesAtaxia & myoclonus are prominent mvmt disorders.
Huntington disease (HD) HTT ADProgressive movement disorders & dementia; psychiatric disturbancesProgressive chorea is prominent.
C9orf72-related amyotrophic lateral sclerosis and frontotemporal dementia C9orf72 ADMvmt disorders, dementia, psychiatric disturbancesMyoclonus, tremor, torticollis
Huntington disease-like 1 (OMIM 603218) 1 PRNP ADRange of clinical features that overlap w/HDEarly onset, slowly progressive
Huntington disease-like 2 JPH3 ADClinically indistinguishable from HDPrevalence highest in (& perhaps exclusive to) persons of African descent
Chorea-acanthocytosis VPS13A ARProgressive mvmt disorder, cognitive & behavior changesMyopathy, ↑ serum CK, acanthocytosis; seizures common; mean onset age ~30 yrs
McLeod neuroacanthocytosis syndrome XK XLCognitive impairment, psychiatric symptomsAcanthocytosis, compensated hemolysis, McLeod blood group phenotype
Benign hereditary chorea (OMIM 118700) NKX2-1 ADChoreaChorea is non-progressive & not assoc w/dementia.
Familial Creutzfeld-Jakob disease (fCJD) (See Genetic Prion Disease.) PRNP ADTypically late onset; progressive dementia; mvmt disorders, behavior changes, & psychiatric symptomsfCJD progresses more rapidly; myoclonus is a prominent involuntary mvmt.
Early-onset familial Alzheimer disease APP
PSEN1
PSEN2 		ADDementiaNo mvmt disorders
Familial frontotemporal dementia w/parkinsonism-17 (FTDP-17) MAPT ADLate onset; progressive movement disorders, dementia, behavior changes; psychiatric disturbancesNo chorea

AD = autosomal dominant; AR = autosomal recessive; CK = creatine kinase; DiffDx = differential diagnosis; MOI = mode of inheritance; XL = X-linked

1.

Huntington disease-like 1 is caused by a specific pathogenic variant (8 extra octapeptide repeats) in the prion protein gene, PRNP, on chromosome 20p [Laplanche et al 1999, Moore et al 2001]. Similar pathogenic variants at this locus also result in other forms of prion disease, such as familial Creutzfeldt-Jakob disease (see Genetic Prion Disease).

From: Spinocerebellar Ataxia Type 17

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