Abstract
BackgroundDown syndrome is characterized by trisomy 21 or partial duplication of chromosome 21. Extensive studies have focused on the identification of the Down Syndrome Critical Region (DSCR). We aim to provide evidence that duplication of 21q21.1-q21.2 should not be included in the DSCR and it has no clinical consequences on the phenotype.Case presentationBecause serological screening was not performed at the appropriate gestational age, noninvasive prenatal testing (NIPT) analysis was performed for a pregnant woman with normal prenatal examinations at 22 weeks of gestation. The NIPT results revealed a 5.8 Mb maternally inherited duplication of 21q21.1-q21.2. To assess whether the fetus also carried this duplication, ultrasound-guided amniocentesis was conducted, and the result of chromosomal microarray analysis (CMA) with amniotic fluid showed a 6.7 Mb duplication of 21q21.1-q21.2 (ranging from position 18,981,715 to 25,707,009). This partial duplication of 21q21.1-q21.2 in the fetus was maternally inherited. After genetic counseling, the pregnant woman and her family decided to continue the pregnancy.ConclusionOur case clearly indicates that 21q21.1-q21.2 duplication is not included in the DSCR and most likely has no clinical consequences on phenotype.
Highlights
Down syndrome is characterized by trisomy 21 or partial duplication of chromosome 21
Our case clearly indicates that 21q21.1-q21.2 duplication is not included in the Down Syndrome Critical Region (DSCR) and most likely has no clinical consequences on phenotype
To delineate the genomic regions associated with a specific Down syndrome (DS) phenotype, several research groups have studied genotype–phenotype correlations by mapping partial duplication of 21 in cases with the DS phenotype, and the concept of DSCR is constantly being improved [4,5,6]
Summary
Down syndrome is characterized by trisomy 21 or partial duplication of chromosome 21. To assess whether the fetus carried this duplication, ultrasound-guided amniocentesis was conducted, and the result of chromosomal microarray analysis (CMA) with amniotic fluid showed a 6.7 Mb duplication of 21q21.1-q21.2 (ranging from position 18,981,715 to 25,707,009) This partial duplication of 21q21.1-q21.2 in the fetus was maternally inherited. The pregnant woman herself has an obviously normal phenotype, without any clinical abnormalities, as based on her medical history and physical examination results. Her prenatal examination results were normal, except for the discovery of the maternally inherited partial duplication 21q21.1-q21.2. After genetic counseling, she and her family decided to continue the pregnancy. The Apgar score of the child at birth was good, and there was no abnormality at the 6-month follow-up
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