[Genetic analysis of a case with a supernumerary marker derived from chromosome 9]

To delineate a small supernumerary marker chromosome (sSMC) derived from chromosome 9 with combined cytogenetic and molecular methods.

For a pregnant woman with fetal ultrasound revealing left ventricular punctate hyperechoic echo, and a high risk for monosomy or partial deletion of chromosome 8, chromosome 9 trisomy, monosomy or partial deletion of chromosome 11 by non-invasive prenatal testing, and an abnormal MOM value revealed by mid-term serum screening, amniocentesis was performed for G banded chromosomal analysis and single nucleotide polymorphism array (SNP-array) assay. Peripheral blood samples of the woman and her spouse were also collected for the above tests. In addition, the woman was further subjected to C banding karyotyping analysis and fluorescence in situ hybridization (FISH) assay.

The G-banded karyotype of the pregnant women was 47,XX,+mar[20]/46,XX[80], whilst C-banding analysis showed a deep stain in the middle of the sSMC (suggestive of centromeric region) and light stain at both ends (suggestive of euchromatism). FISH combined with DAPI banding analysis using 9pter/9qter probes revealed a karyotype of 47,XX,+mar.ish i(9)(9p10)(9p++)[2]/46,XX[18], whilst SNP-array has revealed a 68.1 Mb duplication in the 9p24.3q13 region. A database search has suggested the duplication to be likely pathogenic. No abnormality was found in her fetus and spouse by karyotyping and SNP-array analysis.

Through combined cytogenetic and molecular genetic analysis, a sSMC derived from chromosome 9 was delineated, which has enabled genetic counseling for the couple.