[Analysis of a child with Congenital leukemia and mosaicism trisomy 21 syndrome without GATA1 gene mutation].

Objective: To explore the genetic characteristics and pathogenesis for a child with mosaicism trisomy 21 and Congenital leukemia (CL).

Methods: A child who was admitted to Ningbo Women and Children's Hospital in March 2023 was selected as the study subject. A retrospective analysis was carried out on the clinical data, laboratory test results, immunophenotyping, and genetic characteristics of the child. This study was approved by the Medical Ethics Committee of the Hospital (Ethics No.: EC2024-063).

Results: Whole genome sequencing (WGS) revealed that the child has mosaicism trisomy of chromosome 21, with a ratio of approximately 74%. In addition, copy number variations involving multiple OMIM genes that could explain his clinical phenotype were detected and rated as pathogenic based on the guidelines from the American College of Medical Genetics and Genomics (ACMG). No pathogenic variant was detected with the GATA1 gene. Blood immune typing of the child conformed to the immunophenotype of acute myeloid leukemia.

Conclusion: For children with trisomy 21, even in the absence of GATA1 gene variants, the occurrence of CL should be monitored, and early diagnosis and treatment are of great significance for improving the prognosis.