Screening for the fragile X: how many cells should we analyse?
Since nationwide screening for the fragile X would involve the analysis of thousands of individuals within a short period of time, the number of cells, N, which should be analysed is of fundamental importance. When selecting N, the crucial parameter should be the degree of expression of the fragile site in the affected individuals in the population to be screened. However, this degree of expression is not known, and for routine diagnostic purposes, N = 100 has been accepted by many centers. By taking data from two large series of affected males/females with a known degree of expression (one series from New South Wales, one from Belgium), we have estimated the fraction of affected males/females which would have been missed if the two series were rescreened with the analysis of less than 100 cells. Assuming that the degree of expression within these two series is similar to the degree of expression in all affected individuals within the two populations, the results indicate that a reduction of N in a screening program, say from 100 to 50 cells, would reduce the detection rate between 1 and 5%. The reduction would be greater in females than in males, and greater in the Belgian than in the Australian population.
Tommerup
N
N
John F. Kennedy Institute, Glostrup, Denmark.
Laing
S
S
Christensen
I J
IJ
Turner
G
G
D002452:Cell Count; D005188:False Negative Reactions; D005260:Female; D005600:Fragile X Syndrome / Q000175:diagnosis / Q000235:genetics / Q000517:prevention & control*; D006801:Humans; D008214:Lymphocytes / Q000648:ultrastructure; D008297:Male; D008403:Mass Screening / Q000379:methods*; D012729:Sex Chromosome Aberrations / Q000517:prevention & control*