Low Attributes already have built-in penalties, but there are two things to keep in mind before you start going crazy with additional hindrances.
First, a low Attribute may fail most of the time, but even a threshold: 1 test presents some modicum of difficulty. For ordinary things, someone with a low Attribute will be fine - in other words, someone with Charisma: 1 might not be good at picking up strangers in bars, but would be fine using a dating service or hiring an escort. Similarly, someone with Reaction: 1 might not ever be able to make a bootlegger turn without crashing, but driving down to the Stuffer Shack on Gridguide shouldn't present any problems. Someone who has problems doing everyday things needs to have an additional negative quality (uncouth, infirm, etc.).
Secondly, a low Attribute is ludicrously easy to improve. 25 Karma and five weeks of some type of training, and you can increase an Attribute from 1, the absolute lowest rating, to 3, comfortably average. That's why I tend to think of someone with Body and/or Strength of 1 as a couch potato, rather than an invalid; someone with a Charisma of 1 as socially awkward, rather than a smelly outcast; someone with Logic of 1 as someone who has vegged in front of the tridscreen and not used his brain that much, rather than developmentally disabled.