12.05 Mental retardation: Mental retardation refers to significantly sub-average general intellectual functioning with deficits in adaptive functioning initially manifested during the developmental period; i.e., the evidence demonstrates or supports onset of the impairment before age 22.

The required level of severity for this disorder is met when the requirements in A, B, C, or D are satisfied.

A. Mental incapacity evidenced by dependence upon others for personal needs (e.g., toileting, eating, dressing, or bathing) and inability to follow directions, such that the use of standardized measures of intellectual functioning is precluded;

OR

B. A valid verbal, performance, or full scale IQ of 59 or less;

OR

C. A valid verbal, performance, or full scale IQ of 60 through 70 and a physical or other mental impairment imposing an additional and significant work-related limitation of function;

OR

D. A valid verbal, performance, or full scale IQ of 60 through 70, resulting in at least two of the following:

1. Marked restriction of activities of daily living; or

2. Marked difficulties in maintaining social functioning; or

3. Marked difficulties in maintaining concentration, persistence, or pace; or

4. Repeated episodes of decompensation, each of extended duration.

There are a few things I should point out about the above listing.  If you are going to meet this listing you must have had your mental retardation before age 22.  So this listing does not address those issues of a low IQ acquired later in life.  Like from dementia or a head injury that happened after age 22.  So even if you meet all the other requirements of the listing you will still have to show you were mentally retarded before age 22.  This can be very difficult for those who are older since they will have to find some proof of there condition from many years ago.  The best evidence you can get is IQ exams from when you were young or school records showing special education or learning disability.  I have tried many times to make the argument that someone who meets this listing but does not have proof of onset before age 22 is just as functionally disabled as someone who does have the proof of onset before age 22.  This argument is saying that the individual may not meet but does equal the listing.  This argument is not often successful however because it is the opinion of most at SSA that the listing clearly requires onset age test.  Keep in mind this is just one of the listings that refers to mental disability you should check the rest of the listings under mental disorders to see if your mental condition may meet or equal a different listing. 

Even if you can't prove you meet the above listing, mental retardation when combined with other medical conditions can result in limitations that would show an individual could not work.  Depending on how low the IQ is someone with mental retardation mayhave difficulties with things like complex and maybe even simple tasks.  They may also have difficulty remembering things or working independently.  There are numerous possible mental limitations that could decrease one's ability to work.  When combined with a back condition for example which may limit an individual physically the combination of the physical and mental limitations may show the individual is disabled.