In any of these types of spinocerebellar ataxias (SCA), a different protein with an expanded glutamine repeat undergoes abnormal aggregation and deposition in susceptible neurons. (Refer to Wikipedia's page about Trinucleotide Repeat Disorder). These proteins include ataxin 1, ataxin 2, ataxin 3, which is responsible for Machado–Joseph disease, the Cav2.1 P/Q voltage-dependent calcium channel, ataxin 7, and TATA-binding protein. SCA is difficult to diagnose as there are over 60 different types of this disease. It is a group of genetic diseases characterized by slowly progressive incoordination of gait and often poor coordination of hands, speech, and eye movements.