Osteogenesis Imperfecta



Pathophysiology of osteogenesis imperfecta

1) osteogenesis imperfecta is a congenital disorder of Type I collagen with expression chiefly as brittle bones
2) sometimes can affect joints, ligaments, sclerae, teeth, ears, and skin
3) four clinical types have been described

Signs and Symptoms

1) multiple fractures are hallmarks of the disease
2) highly variable clinically, even among family members

Type 1

3) normal-appearing newborn with multiple fractures apparent in first year of life, flat feet, joint laxity, and blue sclerae

4) hearing loss as middle ear bones fracture and fuse
5) bluish yellow teeth that have misshapen contours
6) fracture frequency decreases as child ages
7) patient can reach normal stature and have normal life span

Type 2

8) fatal in utero or neonatal period owing to respiratory failure

Type 3

9) short stature at birth owing to fractures occurring in utero, abnormal dentition, hearing loss, blue sclera at birth that later become white

Type 4

10) similar to Type 1 but with normal sclerae and more variable symptoms

Characteristic Test Findings

Radiology

bones in osteogenesis imperfecta are thin and curvy

osteogenesis imperfecta  Osteogenesis Imperfecta

arrow shows wavy porous bone in osteogenesis imperfecta

Histology and Gross Pathology

1) absence of collagen fibers in sclerae make them appear translucent and hency blue
2) type 1 fracture callous is so pronounced that it can appear tumor-like

Biochemistry

90% of patients with osteogenesis imperfecta have defective genes for pro-alpha1 (I) and pro-alpha (I)

Inheritance and Epidemiology

1) most cases have autosomal dominant inheritance
2) autosomal recessive inheritance has been reported (mostly Type 3)
3) gonadal mosaicism occurs when phenotypically normal parents have more than one offspring with the condition
4) affected genes are COL1A1 and COL1A2
5) Type 1 has th3 most common sporadic cases

Tips for USMLE

1) other diseases with blue sclerae are Cornelia de Lange’s syndrome and Ehlers-Danlos syndrome
2) in Type 1, fractures occur shortly after birth
3) Type 2 has the worst prognosis

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