A Normal Phenotype Case of a Small Supernumerary Marker Chromosome Chimeric Carrier with 12p11.21p11.21 Duplication

sSMC refers to an additional chromosome added to the karyotype of normal human chromosomes, which can be identified by cytogenetic techniques, but its source and structure cannot be determined, and its size is generally ≤ chromosome 20 during metaphase. The clinical phenotype of patients with sSMC can be normal, or they can show severe clinical manifestations such as growth retardation, intellectual disability, and organic dis-eases.

Draw 3 mL of peripheral blood using a heparin anticoagulant tube. Peripheral blood lymphocytes were cultured for 72 hours and then used to prepare sample slides, perform G-banding, and conduct chromosomal karyotype counting and analysis. Draw 2 mL of peripheral blood using an EDTA anticoagulant tube. DNA was extracted by magnetic bead method, and chromosome copy number variation sequencing (CNV-seq) was performed by MGISEQ-2000 sequencer to analyze chromosomal aneuploidy and chromosome copy number variations above 100 kb.

The karyotype result of peripheral blood chromosomes in the case was 47,XX,+mar[38]/46,XX[17]. CNV-seq detected approximately 1.47 Mb duplications in 12p11.21p11.21 regions with a copy number of 3.

CNV-seq can accurately locate sSMC whose sources and characteristics cannot be identified by traditional chromosomal G-banding technology, which is helpful in determining whether the sSMC of carriers have clinical phenotypic correlation.