Survey of Anti‐human T‐Cell Leukemia Virus Type I Antibody in Family Members of Patients with Adult T‐Cell Leukemia

To evaluate the intrafamilial clustering of HTLV‐I, we examined the sera or plasma of 296 healthy family members of patients with adult T‐cell leukemia (ATL) for anti‐HTLV‐I antibodies. Of 296 subjects, 132 (44.6%) had anti‐HTLV‐I antibodies. Fifty‐nine (41.0%) out of 144 males and 73 (48.0%) out of 152 females were seropositive. The positive rates of antibody to HTLV‐I increased with age, especially between the 30–39 and the 40–49 age groups. Five out of 6 fathers, 3 out of 4 mothers, 31 (60.8%) out of 51 spouses, 40 (63.5%) out of 63 siblings and 46 (33.8%) out of 136 children of patients with ATL had anti‐HTLV‐I antibodies. Of 74 children with an ATL father, 14 (18.9%) were seropositive, while 32 (51.6%) out ot 63 children with an ATL mother were seropositive. This difference was statistically significant (P<0.001). Of those children with an ATL father, 12 (26.1%) out of 46 whose mothers were HTLV‐I carriers had antibodies to HTLV‐I. In contrast, none of the 13 children whose mothers were not carriers were seropositive. These results supported the hypothesis that the mother‐to‐child transmission is one of the most important modes of HTLV‐I transmission. In wives of male patients with ATL, the positive rate of antibody to HTLV‐I was 65.6% (21/32), and in husbands of female patients, it was 52.6% (10/19). The high positive rate of antibody to HTLV‐I not only in wives of male patients but also in husbands of female patients suggests that either HTLV‐I is more frequently transmitted from wives to their husbands than we had originally expected, or that ATL may develop even in wives who acquire HTLV‐I from their husbands after marriage.