This study aimed to semiquantitatively investigate the status of serotonin transporter (SERT) distribution in the brainstem of individuals with MSA-parkinsonian type (MSA-P) via <sup>123</sup>I-2β-carbomethoxy-3β-(4-iodophenyl)nortropane (<sup>123</sup>I-FP-CIT) SPECT and compare it with pathologic findings in some cases. The gene discussed is SLC6A4; the disease is multiple system atrophy.