Mice wi th alleles a t the X-chromosomal locus, Mottled, have connective tissue abnormali t ies tha t are, in m a n y respects, similar to those found in la thyr i t ic animals. Like animals raised on lathyrogens, these mice have aort ic aneurysms, reduced tensile s t rength of the skin, and bone abnormali t ies (1). D a t a is presented to indicate tha t the low tensile s t rength is due to im...