The authors analyzed the concordance of sib pairs of HLA typing in cases
where both sibs had affective illness and where the sibs were discordant.
They detected an excess of HLA similarities in doubly affected sibs and a
lack of similarities in discordant sibs. Therefore, the authors hypothesize
that HLA may be linked with a primary affective disorder susceptibility
locus or it may be associated with such a locus in some other way.