Type I (insulin dependent) diabetes mellitus. Is there strong evidence for a non-HLA linked gene?

A recent investigation of families containing two and three consecutive generations affected with Type I (insulin dependent) diabetes mellitus has led to speculation that there is a second susceptibility gene, not linked to the major histocompatibility complex. These families differ in important respects from families which have provided the strongest evidence for HLA linkage, namely, families with two or more affected siblings. Computer simulations were designed to test the hypothesis that these two types of families were drawn from the same population of insulin dependent patients. The results indicate that this hypothesis is tenable and that the consecutive generation families probably failed to yield strong evidence for an HLA linked susceptibility gene because of ascertainment bias combined with probable incorrect specifications of the mode of inheritance of insulin dependent diabetes.