Extreme variant of enlarged heterochromatin region on chromosome 9Q in a normal child and multiple family members.

Heteromorphisms of chromosome 9 are among the most common variations in the human karyotype. The pericentromeric polymorphisms of chromosome 9 include variations in the size of q-arm heterochromatin, pericentric inversions, and rarely, additional C-band-negative, G-band-positive material. The finding of a polymorphic variant, either in prenatal screening or in chromosomal analysis for phenotypic abnormalities, may cause parental anxiety and initiate genetic counselling. We report a case of a 39-year-old primigravida with unremarkable pregnancy, who had amniocentesis due to advanced maternal age. Chromosomal analysis demonstrated a long arm (q) variant of chromosome 9 with an enlarged heteromorphic area, approximately three times longer than known reported variants. Prenatal analysis demonstated an identical variant in the probands phenotypically normal father, uncle, and paternal grandmother, confirming an apparently "normal" variant.