De novo partial trisomy distal 4q: a case report: We present a case of de novo distal partial trisomy 4q with firstly described chronic cholecystitis, rarely seen hypothyroidism, and bilateral membranous choanal atresia. The patient, a 10-month-old baby girl had dysmorphic facial features as well as neuromotor retardation, congenital hypothyroidism, atrial septal defect (ASD), white matter atrophy in cranial MRI, grade 2 dilatation in pelvicalyceal system of the left kidney, and bilateral ureteral reflux. In peripheral blood chromosome analysis 46, XX, dup(4) (q21q35) karyotype was detected. In FISH analysis using 4p/4q subtelomeric probe; 3 signals for 4 q region and 2 signals for 4p region were observed. In chromosome analyses of her healthy parents, no anomaly was detected. Herein we present a case of de novo partial distal trisomy 4q syndrome to contribute to the literature since it is rarely seen and this is the first patient with partial trisomy distal 4q syndrome presented with chronic cholecystitis and the second patient with hypothyroidism.