[Fragile site Xq27 and metabolism of monocarbons. Significant decrease of the frequency of chromosomal gaps by...

A decrease of frequency of a gap at the extremity of the long arm of the X chromosome (fragile site Xq27) is obtained by adjonction of monocarbons precursors to lymphocytes cultures. The efficacity of the treatments is precised by the analysis of 44 629 mitoses. For the first time, in one patient, parenteral administration of 5-formyl-tetrahydrofolate lead to a clinical improvement with concomitant disappearance of the gap.