(CAG)/Q expansion disorders

A method of measuring progression of a (CAG)n/Qn-expansion disorder, said method comprising:

• obtaining a first sample from an individual;
• combining the first sample with o-phthaldialdehyde under conditions effective to form a first test solution comprising an o-phthaldialdehyde derivative of Nε-(L-γ-glutamyl)-L-lysine;
• determining a first concentration of the o-phthaldialdehyde derivative of Nε-(L-γ-glutamyl)-L-lysine in the first test solution;
• obtaining a second sample from the individual at a time after the first sample is obtained;
• combining the second sample with o-phthaldialdehyde under conditions effective to form a second test solution comprising the o-phthaldialdehyde derivative of Nε-(L-γ-glutamyl)-L-lysine;
• and
• determining a second concentration of the o-phthaldialdehyde derivative of Nε-(L-γ-glutamyl)-L-lysine in the second test solution;
• wherein progression of a (CAG)n/Qn-expansion disorder is indicated by the second concentration being higher than the first concentration.

A method of measuring therapeutic efficacy of a treatment for a (CAG)n/Qn-expansion disorder, said method comprising:

• obtaining a first sample from an individual;
• combining the first sample with o-phthaldialdehyde under conditions effective to form a first test solution comprising an o-phthaldialdehyde derivative of Nε-(L-γ-glutamyl)-L-lysine;
• determining a first concentration of the o-phthaldialdehyde derivative of Nε-(L-γ-glutamyl)-L-lysine in the first test solution;
• providing the individual with a treatment for a (CAG)n/Qn-expansion disorder;
• obtaining a second sample from the individual after said providing the individual with a treatment;
• combining the second sample with o-phthaldialdehyde under conditions effective to form a second test solution comprising the o-phthaldialdehyde derivative of Nε-(L-γ-glutamyl)-L-lysine;
• and
• determining a second concentration of the o-phthaldialdehyde derivative of Nε-(L-γ-glutamyl)-L-lysine in the second test solution;
• and
• comparing the second concentration to the first concentration to measure the therapeutic efficacy of the treatment for a (CAG)n/Qn-expansion disorder, wherein an effective treatment is indicated by the second concentration being lower than the first concentration.