A Fetus with Hb Bart's Disease Due to Maternal Uniparental Disomy for Chromosome 16

We here report an unusual case of Hb Barts (γ4) disease. Thalassemia screening of a couple showed that the wife was an α0-thalassemia (α0-thal) carrier and her husbands mean corpuscular volume (MCV) was normal. Chorionic villus sampling (CVS) was performed at 13 weeks gestation for positive Down syndrome screening and chromosomal study of the cultured CVS showed a normal karyotype. Ultrasound examination at 22 weeks gestation showed fetal cardiomegaly and raised middle cerebral artery peak systolic velocity. Cordocentesis confirmed fetal anemia and showed Hb Barts disease. Multiplex gap-polymerase chain reaction (gap-PCR) for α-thal deletions on DNA extracted from the CVS showed the presence of a homozygous α0-thal - -SEA (Southeast Asian) deletion. The husband was found to be a carrier of the α+-thal -α3.7 (rightward) deletion. Non paternity was excluded by fluorescent PCR using short tandem repeat (STR) markers on chromosomes 13, 18 and 21. A de novo terminal deletion of chromosome 16 was excluded by array comparative genomic hybridization (aCGH). Detection of uniparental disomy (UPD), using STR markers on chromosome 16 showed maternal uniparental isodisomy from 16pter to 16p13.2, and uniparental heterodisomy from 16p13.13 to 16qter.