Constitutional t(11;22)(q23;q11) is the most frequent recurrent non-Robertsonian 
translocation in humans. Balanced carriers of t(11;22) usually manifest no 
clinical symptoms, and are often identified after the birth of offspring with an 
unbalanced form of this translocation, known as Emanuel syndrome. To determine 
the prevalence of the disorder, we sent surveillance questionnaires to 735 core 
hospitals in Japan. The observed number of Emanuel syndrome cases was 36 and 
that of t(11;22) balanced translocation carriers, 40. On the basis of the de 
novo t(11;22) translocation frequency in sperm from healthy men, we calculated 
the frequency of the translocations in the general population. Accordingly, the 
prevalence of Emanuel syndrome was estimated at 1 in 110,000. Based on this 
calculation, the estimated number of Emanuel syndrome cases in Japan is 1063 and 
of t(11;22) balanced translocation carriers, 16,604, which are much higher than 
the numbers calculated from the questionnaire responses. It is possible that 
this discordance is partly attributable to a lack of disease identification. 
Further efforts should be made to increase the awareness of Emanuel syndrome to 
ensure a better quality of life for affected patients and their families.