Huntington's disease phenocopies are clinically and genetically heterogeneous.
Huntington's disease (HD) classically presents with movement disorder, cognitive dysfunction and behavioral problems but is phenotypically variable. One percent of patients with HD-like symptoms lack the causative mutation and are considered HD phenocopies. Genetic diseases known to cause HD phenocopies include HD-like syndromes HDL1, HDL2, and HDL4 (SCA17). HD has phenotypic overlap with dentatorubral-pallidoluysian atrophy, the spinocerebellar ataxias and neuroferritinopathy. Identifying the genetic basis of HD phenocopies is important for diagnosis and may inform the search for HD genetic modifiers. We sought to identify neurogenetic diagnoses in the largest reported cohort of HD phenocopy patients. Two hundred eighty-five patients with syndromes consistent with HD, who were HD expansion-negative, were screened for mutations in PRNP, JPH3, TBP, DRPLA, SCA1, SCA2, SCA3, FTL and FRDA. Genetic diagnoses were made in 8 subjects: we identified 5 cases of HDL4, 1 of HDL1 and 1 of HDL2. One patient had Friedreich's ataxia. There were no cases of DRPLA, SCA1, SCA2, SCA3, or neuroferritinopathy. HD phenocopies are clinically and genetically diverse and a definitive genetic diagnosis is currently possible in only a minority of cases. When undertaken, it should be clinically directed and patients and clinicians should be prepared for the low probability of reaching a genetic diagnosis in this group of patients.
Wild
Edward J
EJ
Department of Neurodegenerative Disease, UCL Institute of Neurology/National Hospital for Neurology and Neurosurgery, Queen Square, London, United Kingdom.
Mudanohwo
Ese E
EE
Sweeney
Mary G
MG
Schneider
Susanne A
SA
Beck
Jon
J
Bhatia
Kailash P
KP
Rossor
Martin N
MN
Davis
Mary B
MB
Tabrizi
Sarah J
SJ
D000328:Adult; D015331:Cohort Studies; D003937:Diagnosis, Differential; D005260:Female; D005621:Friedreich Ataxia / Q000175:diagnosis / Q000235:genetics; D006801:Humans; D006816:Huntington Disease / Q000175:diagnosis*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D008875:Middle Aged; D009069:Movement Disorders / Q000175:diagnosis* / Q000235:genetics*; D016254:Mutagenesis, Insertional; D010641:Phenotype; D017096:Prion Diseases / Q000175:diagnosis / Q000235:genetics; D000072002:Prion Proteins; D011328:Prions / Q000235:genetics; D013577:Syndrome; D035181:TATA-Box Binding Protein / Q000235:genetics
D008565:Membrane Proteins; C512656:PRNP protein, human; D000072002:Prion Proteins; D011328:Prions; D035181:TATA-Box Binding Protein; C509817:TBP protein, human; C412507:junctophilin