Most individuals with osteogenesis imperfecta (OI) are heterozygous for dominant 
mutations in one of the genes that encode the chains of type I collagen. Each of 
the more than 30 mutations characterized to date has been unique to the affected 
member(s) of the family. We have determined that two individuals with a 
progressive deforming variety of OI, OI type III, have the same new dominant 
mutation [alpha 1(I)gly154 to arg] and that two unrelated infants with perinatal 
lethal OI, OI type II, share a second new dominant mutation [alpha 1(I)gly1003 
to ser]. These mutations occurred at CpG dinucleotides, in a manner consistent 
with deamination of a methylated cytosine residue, and raise the possibility 
that CpG dinucleotides are common sites of recurrent mutations in collagen 
genes. Further, these findings confirm that the OI type-III phenotype, 
previously thought to be inherited in an autosomal recessive manner, can result 
from new dominant mutations in the COL1A1 gene of type-I collagen.