Background and objective:  Huntington's disease (HD) is an autosomal dominant disorder that mainly affects adults. Although mutations in the IT15 gene have been known as the main cause of the disease, patients with HD like (HDL) syndrome have mutations in genes other than the IT15 gene.  In this study, we investigate the frequency of mutations in SCA17/TBP, JPH3 and PRNP genes in patients with HDL syndrome.
 
      Methods: The frequency of mutations in SCA17/TBP, JPH3 and PRNP genes was studied in 56 patients with HDL phenotype but without trinucleotide expansion in the IT15 gene. DNA was extracted from peripheral whole blood by the salting out method. PCR was performed using specific primers for each gene. PCR products were separated on polyacrylamide gel. Sequencing was performed on some samples to confirm the PCR results.
 
      Results: We found neither trinucleotide expansion in the JPH3 and SCA17, nor octapeptide insertion in the PRNP gene.
 
      Conclusion: Based on the results, Iranian patients with HDL syndrome do not have mutation in the TBP, JPH3 and PRNP genes. However, this result may be due to population differences, rarity of the mutations in the studied genes and the small number of study subjects. Therefore, studies with a larger study population that investigate other mutations, such as point mutations in the mentioned genes may help clarify the exact cause of HDL phenotype in Iranian patients.