Classification of Sillence et al for Osteogenesis Imperfecta

Description

Osteogenesis Imperfecta (OI, "brittle bone disease") is an inherited defect in Type I collagen that results in increased bone fragility. Sillence et al used clinical and radiographic findings to identify different types of the condition.

Group characteristic: bone fragility with fracture after relatively mild trauma

Other findings associated with the defective collagen: blue sclerae, dentinogenesis imperfecta, hearing loss, cardiopulmonary abnormalities, easy bruisability, and loose joints.

Findings	OI Type I	OI Type II
term		perinatal lethal
inheritance	autosomal dominant	autosomal dominant or recessive, new mutations
bone fragility	generally mild, minimal to moderate	very severe
sclerae	distinctive blue at all ages	blue-gray in infancy
deformity	usually absent	develop if survive
other findings	presenile hearing loss, easy bruisability	often stillbirth or neonatal death; with optimal care may survive into childhood; small hands and feet (micromelia)

Findings	OI Type III	OI Type IV
term	progressive deforming
inheritance	autosomal dominant or recessive	autosomal dominant
bone fragility	moderate to severe	moderate to severe, may have prenatal fractures, decreases during puberty
sclerae	may be blue in infancy, normal later	blue or grayish in infancy, may be normal later
deformity	variable but usually severe of long bones and spine; stunted stature	variable in spine and long bones
other findings	stunted stature; may die in childhood from respiratory complications	moderately short stature, hearing loss

Findings	OI Type I Subgroup A	OI Type I Subgroup B
dentinogenesis imperfecta	absent	present

Findings	OI Type II Subgroup A	OI Type II Subgroup B	OI Type II Subgroup C
inheritance	autosomal dominant	(?) autosomal recessive	(?) autosomal recessive
long bones	crumpled	broad and crumpled	thin and fractured
ribs	broad with continuous beading	beading absent or discontinuous	thin and beaded

Findings	OI Type IV Subgroup A	OI Type IV Subgroup B
dentinogenesis imperfecta	absent	present

Genetic findings (Table 205-4, Byers):

(1) Type I: pro-alpha 1(1) (COL1A1) null

(2) Type II: pro-alpha 1(1) (COL1A1) and pro-alpha 2(1) (COLIA2) substitutions for glycine exon-skipping partial gene deletions; C-terminal propeptide mutations that interfere with chain association

(3) Type III: pro-alpha 1(1) (COL1A1) and pro-alpha 2(1) (COLIA2) substitutions for glycine exon-skipping; pro-alpha 1(1) (COL1A1) mutations that prohibit gene associations

(4) Type IV: pro-alpha 1(1) (COL1A1) and pro-alpha 2(1) (COLIA2) substitutions for glycine exon-skipping partial gene deletions

Limitations:

• The Sillence classification scheme is not adequate to describe many cases.

• The osteogenesis imperfecta phenotype is essentially continuous, with substitution for any glycine in the triple helix and skipping of any exon.

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Description

Specialty

Objective

ICD-10