title: CTG repeat number at the myotonic dystrophy locus in healthy Kuwaiti individuals: possible explanation of why myotonic dystrophy is rare in Kuwait.
abstract: BACKGROUND
  Myotonic dystrophy is caused by unstable (CTG)(n) repeat expansion. On normal chromosomes, this repeat is highly polymorphic, with a copy number ranging from 4 to 38. Myotonic dystrophy is considered more prevalent in Western European and Japanese populations but less prevalent, rare, or even absent in others. It has been proposed that the expanded (CTG)(n) alleles originated from the group of the large normal alleles.
  
  
  OBJECTIVE
  To determine whether there is a lower prevalence of the large alleles in the Kuwaiti population.
  
  
  METHODS
  We determined the size distribution of the CTG repeats by means of polymerase chain reaction in blood DNA derived from 185 healthy Kuwaiti individuals representing the 5 Kuwaiti provinces.
  
  
  RESULTS
  We found a total of 17 (CTG)(n) alleles, with a range of 5 to 37 repeats. The (CTG)(5) allele was the most frequent single allele (100/370 [27.0%]), whereas the (CTG)(10-13) was the most frequent class of alleles (161/370 [43.5%]). Using 18 repeats as the cutoff point, chi(2) analysis showed a statistically significant lower frequency of greater than 18 alleles in the Kuwaiti population compared with the European population (chi(2) = 12.7; P<.001).
  
  
  CONCLUSIONS
  These data may explain the rare occurrence of myotonic dystrophy in the Kuwaiti population. Further study of healthy families within the high-normal repeat range is in progress to investigate the possible instability of the (CTG)(>18) alleles in our area.
authors.affiliation: Department of Medical Laboratory Sciences, Faculty of Allied Health Sciences and Nursing, Kuwait University, Sulaibekhat, Kuwait. s.alfadhli@hsc.kuniv.edu.kw
authors.forename: Suad
authors.initials: S
authors.lastname: Alfadhli
authors.forename: Alaa E
authors.initials: AE
authors.lastname: Elshafey
authors.forename: Lailá
authors.initials: L
authors.lastname: Bastaki
authors.forename: Sadeqa
authors.initials: S
authors.lastname: Al-Awadi
mesh_terms: D016009:Chi-Square Distribution; D005787:Gene Frequency / Q000235:genetics; D006801:Humans; D007730:Kuwait; D009223:Myotonic Dystrophy / Q000235:genetics*; D040641:Quantitative Trait Loci / Q000235:genetics*; D019680:Trinucleotide Repeat Expansion / Q000235:genetics*