Folate sensitive site at 10q23 and its expression as a deletion.

A patient is reported for whom initial chromosome analysis indicated 45,X/46,XX/46,XX,10q- mosaicism. The clinical findings included hypothyroidism and a low red cell folate estimation. The deleted chromosome 10 was subsequently shown to be an extreme expression of the folate sensitive heritable fragile site at 10q23, and a possible association between this and the in vivo folate status of the patient is suggested.