Prenatal diagnosis of interstitially satellited 6p.

OBJECTIVES

To present the prenatal diagnosis of de novo interstitially satellited 6p and a review of the literature.

CASE: An amniocentesis was performed at 18 weeks' gestation because of paternal balanced translocation, t(6;14)(p22;p12). Family history of the father showed the derivative chromosomes to be transmitted through at least two generations with three members affected with partial trisomy 6p (6p22 --> 6pter).

RESULTS

Cytogenetic analysis of the cultured amniocytes revealed an interstitial insertion of a nucleolar organizer region (NOR) in 6p22 and a karyotype of 46,XX, rec(6)ins(6;14)t(6;14)(6pter --> 6p22::14p12 -->14p12::6p22 --> 6qter). Level II ultrasound examinations revealed normal findings. The parents opted to terminate the pregnancy. A 650-g fetus was delivered at 23 weeks' gestation without any gross abnormalities. Cytogenetic analysis of the cord blood lymphocytes confirmed the prenatal diagnosis.

CONCLUSIONS

The present case provides evidence that a de novo interstitial insertion of a NOR into a nonacrocentric chromosome can be derived from a parental balanced reciprocal translocation involving the satellite stalk region of an acrocentric chromosome. The NOR-inserted chromosome seems to be a harmless variant. However, a de novo interstitial NOR translocation can be pathogenic if there is genomic disruption at the site of translocation, which should be included in genetic counseling and perinatal investigation.