Osteogenesis Imperfecta (OI)

Pathophysiology
1. OI is an inherited connective tissue disorder that primarily affects bone (Martin & Shapiro, 2007). It is caused by mutations in various collagen producing genes (Rush, 2016). There are currently 8 known types.
  1. Mutations in COL1A1, COL1A2, CRTAP, and P3H1 genes cause OI (GHR, 2018)
    1. COL1A1 and COL1A2 genes, cause more then 90% of all cases of OI, and are inherited via an autosomal dominant pattern (GHR, 2018).
      1. COL1A1 and COL1A2 provide instructions for making proteins that are used to assemble type I collagen (GHR, 2018).
    2. OI can also have an autosomal recessive pattern of inheritance, especially when it is caused by mutations in the CRTAP or P3H1 gene, which cause rarer, severe forms of OI (GHR, 2018).
      1. Proteins produced from CRTAP or P3H1 genes process collagen into its mature form, therefore mutations in them disrupt the normal folding, assembly, and secretion of collagen molecules, thus weakening connective tissues (GHR, 2018).
  2. Infants with more severe forms of OI, including type II and III, have no family history of OI. In these infants, the condition is caused sporadic mutations in the COL1A1 or COL1A2 gene (GHR, 2018).
  3. The etiology of OI type V and OI type VI is unknown, as there are currently no identified mutations causing them (GHR, 2018).
Epidemiology
Nursing Considerations
1. Psychosocial Support
  1. Reassure parents not to feel guilty regarding child’s diagnosis & refer to genetic counsellor
  2. Educate parents on how OI does not affect a child’s ability to think and learn
  3. Offer various resources such as: Osteogenesis Imperfecta Foundation website (www.oif.org) and phone number: 1-800-981-2663 - Referrals to local OI support group, pediatrician, pediatric orthopedist, physical therapist should be provided
2. Handling
  1. - Educate parents with demonstration and explanation of proper holding, lifting, feeding and general infant care procedures - Get to parents to do a return demonstration to ensure learning has occurred - Provide reading material and educational resources such as brochures from OI foundation etc. - Provide teaching regarding recognizing new fractures and protecting the injured body part while travelling to the hospital or clinic - Advise parent regarding choosing clothing with wide openings since it’d allow for the garment to slide over the infant’s arms or legs without pulling the limbs
3. Bedding and positioning
  1. Waterbeds and soft bedding should never be used - Regular crib mattress is recommended for a baby with OI - Position the infant to prevent plagiocephaly: use rolled blankets/sheets or soft foam to support side lying position
4. Parent teaching
  1. - Educate parents with demonstration and explanation of proper holding, lifting, feeding and general infant care procedures - Get to parents to do a return demonstration to ensure learning has occurred - Provide reading material and educational resources such as brochures from OI foundation etc. - Provide teaching regarding recognizing new fractures and protecting the injured body part while travelling to the hospital or clinic - Advise parent regarding choosing clothing with wide openings since it’d allow for the garment to slide over the infant’s arms or legs without pulling the limbs
5. Feeding
  1. - Small, frequent feeds: babies may be poor feeders and may have weak sucking reflex - Breast milk recommended: excellent source of nutrition • Fosters special bond between mother and child • If infant unable to breastfeed due to inability to suck or risk of aspiration due to rapid respirations: offer mom to pump breast milk and feed the child from a bottle - Burp the baby cautiously: gently lift the baby and soft taps with padding over hands are recommended
Clinical Manifestations (OI, n.d.)
1. Type I: Most common/ mildest form
  1. Bones break easily, usually before puberty, but minimal bone deformity
  2. Sclera have a grey, blue, or purple tint
  3. Brittle teeth
  4. Decreased amount of collagen, but normal structure
  5. Muscle weakness
  6. Spinal curvature
  7. Hearing loss, starting in the 20s-30s
  8. Triangular shaped face
2. Type II: Most severe
  1. Death at birth, or soon after birth, as a result of respiratory compromise due to under developed lungs
  2. Small stature
  3. Many fractures & severe bone deformity
  4. Abnormally structured collagen
  5. Tinted sclera
3. Type IV
  1. Similar to Type I & III, with whiter sclera
4. Type III
  1. Similar to Type I
    1. Bones fracture easily, with fractures present at birth
    2. Possible respiratory issues
    3. Barrel-shaped rib cage
    4. Improperly formed collagen
5. Type V
  1. Similar to Type IV, with normal teeth
    1. Bone has mesh-like appearance under microscope
    2. Restricted forearm rotation due to calcification of the interosseous membrane
    3. Abnormally large hypertrophic calluses at fracture sites
    4. Radio-opaque band seen on growth plate of long bones
6. Type VI
  1. Similar to Type IV
    1. Bone has a fish scale appearance under microscope
7. Type VII
  1. Similar to Type IV, but results from recessive inheritance of a mutation to the CRTAP gene (Ward et al., 2002)
8. Type VIII
  1. Similar to Type I or II
    1. White sclera
    2. Extreme skeletal under mineralization.
    3. Severe growth deficiency
Treatment
Diagnosis: (NIH, n.d.)
1. OI diagnosed prenatally, at birth or at a young age, unless the condition is a milder form, in which diagnosis can take place in the teenage or adult years (OIF, 2015)
  1. Family history
  2. Clinical presentation (Frequent fractures, sclera colour change, teeth deformities, hearing loss, etc.)
  3. X-rays: fractures that are at different stages of healing; Wormian bones of the skull; "codfish vertebrae" of the spine
  4. Biochemical testing: collagens taken from a small skin biopsy, where changes in type I collagen are an indication of OI
  5. DNA sequencing: COL1A1 and COL1A2 is used to identify the type I collagen gene mutation responsible for the altered collagen protein Children need additional testing of less common collagen genes (CRTAP and P3H (LEPRE1)) responsible for some of the rare recessive forms of OI

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Osteogenesis Imperfecta (OI)

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