An analphoid marker chromosome inv dup(15)(q26.1qter), detected during prenatal diagnosis and characterized via chromosome microdissection.

ABSTRACT

A small, mosaic, C-band negative marker chromosome was detected in amniocyte cultures during prenatal diagnosis due to advanced maternal age. Following spontaneous premature labor at 29 weeks gestation, a dysmorphic infant was delivered, with flat nasal bridge, short palpebral fissures, micrognathia, high forehead, low-set ears, telecanthus and corneal dystrophy. Additional folds of skin were present behind the neck, and feet, fingers and toes were abnormally long. The child died at age five days, after two days of renal failure. The origin of the marker chromosome was subsequently identified from a cord blood sample, via chromosome microdissection. Through reverse FISH, we found the marker to be an inverted duplication of the region 15q26.1-->qter. FISH with alphoid satellite probe was negative, while whole chromosome 15 paint was positive. Both ends of the marker chromosome were positive for the telomeric TTAGGG probe. These data, plus the G-banding pattern, identified the marker as an analphoid, inverted duplicated chromosome, lacking any conventional centromere. We discuss the etiology and clinical effects of this marker chromosome, comparing it to the few reported cases of "tetrasomy 15q" syndrome. We also discuss the possible mechanisms that are likely responsible for this neocentromere formation.