The three most distally located HI-genes that could contribute to this common 6q terminal deletion phenotype are TBP (Tata Box-Binding Protein, MIM*600,075), PSMB1 (Proteasome Subunit Beta-Type 1, MIM*602,017) and DLL1. TBP is known to cause late-onset neurological disorders such as spinocerebellar ataxia (MIM#607136) and Parkinson’s disease (MIM#168600) through expansion of a CAG repeat [39], but it is unclear whether loss of function of one allele has a phenotypic affect. This evidence concerns the gene PSMB1 and cerebellar ataxia.