Missing limbs or sensory organs appear at multiple spots in the rules!
There are two places where missing or defective limbs show up in the rules.
Flaw
The One Arm Flaw for 3 points, as identified by CatLord.
One Arm (3 pt. Flaw) You were either born with only one arm or lost your arm through an injury of some sort. You suffer no secondary-hand penalty, since you have adapted to using your one hand for most activities. When you need to use two hands, however, you lose two dice from your dice pool. Your running speed in Hispo and Lupus form is 1/2 of normal. Metis characters may take this Flaw (for no freebie points) as their inherent deformity.1
Battle Scar
There's also the Battlescar of Maimed Limb,
Maimed Limb: One of your limbs has been mauled
to the point of uselessness. If you lost a leg, you move at
half speed in all forms. If you lost an arm, your Hispo and
Lupus speed is reduced to three-quarters. You are not able to
use the damaged limb for any purpose. 2
Difference
There is a substantive difference between the two: The One Arm-Flaw costs 2 dice on twohanded things, and reduces speed by 50%. The Maimed Limb Battlescar reduces speed by 25% for arms (and 50% for legs), but does not specify a penalty for twohanded things specifically. That is still faster than Lame, which is a reduction of speed by 75% and bans running:
Lame (3 pt. Flaw)
Either from birth, an accident, or a major battle scar,
your legs are damaged, which prevents you from running
or walking easily. You have a pronounced limp and may
need assistance from a cane or walking stick. Your walking
speed is one-quarter that of a normal human, and running
is impossible. Metis characters may take this Flaw (for no
freebie points) as their metis disfigurement.1
Is it special?
No. One Arm & Lame are not the same result as Maimed Limb rules-wise. Very similar to the damaged limb, is damage to the eyes, which exists both as a Battle Scar and a Flaw, and they are not identically worded or reference one another.
One Eye (2 pt. Flaw)
You lack depth perception and have limited vision,
due to the fact that you only have one eye. Your blind
side has no peripheral vision. The difficulties of all Perception
rolls involving eyesight are increased by two, and
when depth perception is involved (such as during ranged
combat), the difficulty is increased by an additional +1.3
Missing Eye: One of your eyes was gouged out and
hasn’t grown back. The difficulties on all rolls involving
depth perception or weapon firing (including using thrown
weapons) increase by three. Any Perception rolls based
on sight take a +2 difficulty penalty.2
The difference here? Missing eye increases the difficulty for depth perception by 3, One eye only by 1.
1 - W20, p.474.
2 - W20, p.260.
3 - W20, p.473.