Case Report: Rare triple-line chromosome 9 mosaicism (47,XX,+del(9)(q13)/47,XX,+9/46,XX) associated with severe neurodevelopmental impairment and congenital anomalies

Background Chromosome 9 abnormalities are rare. Full trisomy 9 is mostly incompatible with postnatal survival, whereas mosaic trisomy 9 permits survival with highly variable clinical manifestations. Triple-line mosaicism involving both full trisomy 9 and structural chromosome 9 abnormalities is exceptionally rare. Case Presentation A 1-year-old girl, conceived via IVF, had normal nuchal translucency and NIPT. Prenatal ultrasound showed a single umbilical artery, lower abdominal cyst, borderline ventriculomegaly at 28 weeks, and late polyhydramnios. She was born at 40 weeks, 3,430 g, 49 cm, head circumference 36 cm, Apgar 8/9/9, requiring mild oxygen supplementation. At age 1 year, she exhibited dysmorphic facial features (prominent forehead, hypertelorism, upslanting palpebral fissures, short philtrum, low-set mildly dysplastic ears, retrognathia), bilateral ovarian cysts, minimal clinodactyly of the right fifth finger, palmar and plantar crease abnormalities, hemodynamically significant patent ductus arteriosus (PDA), patent foramen ovale (PFO), previously closed muscular ventricular septal defect (VSD), severe hypotonia, global developmental delay, convergent strabismus, and feeding difficulties requiring gastrostomy. Cranial ultrasound revealed ventriculomegaly, grade II intraventricular hemorrhage, slightly thin corpus callosum, and altered posterior cranial fossa. Postnatal genetic evaluation, including array CGH (comparative genomic hybridization), conventional karyotyping, FISH (fluorescent in situ hybridization), and QF-PCR (Quantitative Fluorescence Polymerase Chain Reaction), identified a complex mosaicism comprising three cell lines: 47,XX,+del(9)(q13)60%/47,XX,+920%/46,XX20%. Conclusion This case expands the phenotypic spectrum of chromosome 9 mosaicism and highlights the diagnostic value of multimodal genomic analysis for accurate detection and counselling.