Investigation of three patients with the "ring syndrome", including familial transmission of ring 5, and estimation of reproductive risks.

We report three cases of ring chromosome 5 [r(5)], two familial (mother and daughter) and one sporadic. The phenotype resembled that of the "ring syndrome" with prenatal onset of short stature, growth retardation, mild facial dysmorphism and normal psychomotor development. Extended metaphase and prometaphase chromosome preparations using G-, R- and Q-banding and scanning electron microscopy (SEM) failed to demonstrate deletion in the ring 5. Flow karyotype using the FACS cell sorter and peak area analysis showed the r(5) to be in the same position as the normal chromosome 5. The deletion that is presumably associated with ring formation appears to involve less that one megabase of DNA. In the "complex" rings, high resolution SEM showed fragile sites at the 5q34 and 5q35 region with frequent deletions at that site. A literature survey suggests that when a parent carries a ring chromosome about 80% of recognised pregnancies result in live birth. Of these, about half have a normal phenotype and karyotype, and half inherit the parental ring; about half of those acquiring the ring (20%) show significant mental retardation.