This finding could have a remarkable clinical significance, considering that the prevalence of B-cell lymphopenia among HD patients is very high (3, 9–13, 41, 42): 57.7% of our patients had a CD19+ B cell count < 100 cells/μL, and this selective B-cell lymphopenia worsened after 12 months of follow-up. The gene discussed is CD19; the disease is Huntington disease.