A Rare Double Aneuploidy Case (Down-Klinefelter).

Area of Science:

• Genetics
• Pediatrics
• Endocrinology

Background:

• Down syndrome (47,+21) is characterized by specific dysmorphic features, intellectual disability, and hypotonia.
• Klinefelter syndrome (49,XXY) is a numerical chromosomal abnormality impacting male development.
• Co-occurrence of these syndromes presents unique diagnostic and clinical challenges.

Observation:

• A 4-month-old male infant presented with classic Down syndrome phenotypes.
• The patient exhibited hypothyroidism and multiple congenital heart defects: atrial septal defect, ventricular septal defect, and patent ductus arteriosus.
• No apparent phenotypic manifestations of Klinefelter syndrome were observed.

Findings:

• Karyotype analysis revealed a rare 48,XXY,+21 chromosomal complement.
• This genetic finding represents a unique co-occurrence of Down syndrome and Klinefelter syndrome.
• The absence of Klinefelter phenotypic signs in the presence of the XXY karyotype is noteworthy.

Implications:

• Highlights the variability in phenotypic expression for combined chromosomal abnormalities.
• Emphasizes the importance of genetic testing for accurate diagnosis in complex pediatric cases.
• Contributes to the understanding of genotype-phenotype correlations in Down and Klinefelter syndromes.