Unusual chromosome 9 variant with an extra G-dark and C-negative segment in the short arm, proximal to the centromere: a case study.

: Polymorphic variation of constitutive heterochromatin in human chromosomes is commonly seen in clinical cytogenetic analyses. Normal variant can be confirmed with C-banding and are generally considered clinically insignificant. However, it may be a concern if an unusual variant chromosome is detected in a prenatal specimen. We report an unusual chromosome 9 variant with an extra G-dark and C-negative segment in the short arm, proximal to the centromere. This chromosome 9 variant has been previously reported in only nine independent families. Whether this is a rare variant or an underestimation requires further evaluation. Of note is that all probands so far reported in the literature are clinically normal.