Osteogenesis imperfecta type IV. Detection of a point mutation in one alpha 1(I) collagen allele (COL1A1) by RNA/RNA hybrid analysis.
We have identified a point mutation in one alpha 1(I) collagen allele (COL1A1) of a child with the type IV osteogenesis imperfecta phenotype. When compared to parental and control samples, skin fibroblasts of the proband synthesized two populations of type I collagen molecules. One population was normal; the other was delayed in secretion and electrophoretic migration due to post-translational overmodification. Two-dimensional gel electrophoresis of the CNBr peptides demonstrated a gradient of overmodification beginning near the carboxyl-terminal CB peptides. This predicts that the mutation delaying helix formation is near the carboxyl-terminal end of one of the component chains of type I collagen. The mRNA of the patient was probed with overlapping antisense riboprobes to type I collagen cDNA. Cleavage of a mismatch in RNA/RNA hybrids of RNase A allowed the location of the mutation to a 225-base pair region of alpha 1(I) cDNA. The mismatch was not present in RNA/RNA hybrids from either parent. This region of both alpha 1(I) alleles of the patient was isolated by screening a lambda ZAP cDNA library. Sequence determination of both alleles demonstrated a single nucleotide change, G----A, resulting in the substitution of a serine for a glycine at amino acid residue 832. This point mutation occurs in the coding region for alpha 1(I) CB6 and is concordant with the protein data. The finding of a glycine substitution in an alpha 1(I) chain of a patient with the milder type IV osteogenesis imperfecta phenotype requires modification of current molecular models for types II and IV osteogenesis imperfecta.
Marini
J C
JC
Unit on Connective Tissue Disorders, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
Grange
D K
DK
Gottesman
G S
GS
Lewis
M B
MB
Koeplin
D A
DA
D000483:Alleles; D000595:Amino Acid Sequence; D001345:Autoradiography; D001483:Base Sequence; D003094:Collagen / Q000235:genetics*; D015180:Electrophoresis, Gel, Two-Dimensional; D005260:Female; D006801:Humans; D007223:Infant; D008969:Molecular Sequence Data; D009154:Mutation; D009693:Nucleic Acid Hybridization; D010013:Osteogenesis Imperfecta / Q000235:genetics*
D003094:Collagen