We report a group of 252 patients with a Huntington's disease-like (HDL) 
phenotype, including 60 with typical Huntington's disease, who had tested 
negative for pathological expansions in the IT15 gene, the major mutation in 
Huntington's disease. They were screened for repeat expansions in two other 
genes involved in HDL phenotypes: those encoding the junctophilin-3 (JPH3/HDL2) 
and prion (PRNP/HDL1) proteins. In addition, because of the clinical overlap 
between patients with HDL disease and autosomal dominant cerebellar ataxia or 
dentatorubral and pallidoluysian atrophy (DRPLA), we investigated trinucleotide 
repeat expansions in genes encoding the TATA-binding protein (TBP/SCA17) and 
atrophin-1 (DRPLA). Two patients carried 43 and 50 uninterrupted CTG repeats in 
the JPH3 gene. Two other patients had 44 and 46 CAA/CAG repeats in the TBP gene. 
Patients with expansions in the TBP or JPH3 genes had HDL phenotypes 
indistinguishable from Huntington's disease. Taking into account patients with 
typical Huntington's disease, their frequencies were evaluated as 3% each in our 
series of typical HDL patients. Interestingly, incomplete penetrance of the 46 
CAA/CAG repeat in the TBP gene was observed in a 59-year-old transmitting, but 
healthy, parent. Furthermore, we report a new configuration of the expanded TBP 
allele, with 11 repeats on the first polymorphic stretch of CAGs. Expansions in 
the DRPLA gene and insertions in the PRNP gene were not found in our group of 
patients. Further genetic heterogeneity of the HDL phenotype therefore exists.