Modeling Osteogenesis Imperfecta in GURPS

Osteogenesis imperfecta (OI) is a congenital disease where the body doesn't produce collagen in sufficient quantity or quality, depending on the specific type the subject has. Due to this, people with the disease break bones very easily. It's more commonly referred to as Brittle Bone Disease.

OI Can generally be split into 3 Types:

• OI Type 1- the mildest form of the disease.
• OI Type 2- normally fatal within the first year of life
• OI Types 3+- Moderate to severe types of the disease with differing clinical presentations

My friend has OI Type 4, which is a moderate to severe type. They broke her foot attempting to walk across concrete in socks. Accidentally kicking the leg of their bedframe broke their toe. A fall in the kitchen broke their elbow. They've cracked ribs, herniated a disk in their back, and had a metal plate in their elbow to correct a break from before I met them. To say that OI doesn't seem like an appealing Player Character trait is entirely accurate, as I'll illustrate below.

OI leads to numerous effects that could be relevant to a GURPS character, which I'd consider core to the trait:

• Propensity for bone breaks
• Hypermobility (A propensity for dislocated joints)
• Chronic pain
• Distinctive Blue Sclera

Let's start by modeling the bone breaks. Let's flip Injury Tolerance (Unbreakable Bones) on its head, and then address the duration of crippling injury.

Injury Vulnerability (Easily Broken Bones) [-10 or -20]: Your body is especially vulnerable to crippling injury.
Mild: Your limbs become crippled when they take damage over HP/4. Your extremities become crippled when they take damage over HP/6. -10 Points.

Severe: Your limbs and extremities become crippled when they take damage over HP/10. -20 points.

Injury Vulnerability (Long-lasting Crippling) [-10]: When you roll HT to see if a crippling Injury is Temporary or Lasting, you roll at HT-4.

Now for modeling the frequent dislocations, I suggest using the rules for Bad Back- the rules fit suffering painful dislocations very well.  

Likewise, Chronic Pain also works right out of the basic set. I could see mixing the triggers of Bad Back and the effects of Chronic Pain to simulate bouts of pain triggered by unwise physical activity, which is true to my experiences with my friend.

Distinctive Features covers the Blue Sclera as a Quirk.

Now in real life, OI can lead to additional effects, some of which will come down to a case-by-case basis:

• Hunchback, per basic set, in the case of deforming types of OI
• Lame (Crippled Legs or Paraplegic), or One Arm, or No Manipulators in the case where OI leads to compression of the spine, resulting in nerve damage that causes one to use the use of their arms/legs.
• Loss of Basic Move

And for Cinematic Icing:

• Flexibility (Double-Jointed), if the Hypermobility has beneficial uses, although people with Ehlers' Danlos Syndrome are better fits for it.
• Bonuses to Weather Sense, or Detect (Low Pressure Atmospheric Conditions) since we all know bone breaks react to atmospheric pressure.