Does anyone have an idea as to how many people (worldwide) are effected by disorders resulting from a misfunction of the ribosomes?

None, if you have a mutated ribosome you are never born or the cell dies via apoptosis.

Don't know about the numbers mate, but a quick google came up with this:

 

http://www3.niddk.nih.gov/fund/other/ribosomes/index.htm

 

With the recent discovery of a ribosomal protein defect in some cases of Diamond-Blackfan Anemia, exploration into how the ribosomes could cause this disease, as well as others, needs to take place

 

Also:

http://www.jneurosci.org/cgi/content/abstract/25/40/9171

Ribosome Dysfunction Is an Early Event in Alzheimer's Disease

 

Qunxing Ding,1 William R. Markesbery,2,3 Qinghua Chen,3 Feng Li,3 and Jeffrey N. Keller1,3

 

Departments of 1Anatomy and Neurobiology and 2Pathology and Neurology and 3Sanders-Brown Center on Aging, University of Kentucky, Lexington, Kentucky 40536-0230

 

 

Alzheimer's disease (AD) is a progressive and devastating disorder that is often preceded by mild cognitive impairment (MCI). In the present study, we report that in multiple cortical areas of MCI and AD subjects, there is a significant impairment in ribosome function that is not observed in the cerebellum of the same subjects.

 

I take it, that is what you meant in your OP.

Thanks for the answer