How prevalent is the disease in the population (include statistics)?

About one in every 27 Ashkenazi Jewish people in the United States is a carrier of the mutated Tay Sachs gene.  The carrier rate in the general population is about one in 250 people.  In the Irish American population about one in every 50 people is a carrier of this disease.  About Sixteen cases of Tay Sachs disease are diagnosed in the United States each year.
  
http://www.who.int/genomics/public/geneticdiseases/en/index2.html#ts
http://kidshealth.org/parent/medical/genetic/tay_sachs.html