Síndrome de Down por trisomía 21 regular asociado a traslocación robertsoniana 13;14 de origen materno en el producto de un embarazo gemelar biamniótico

background. robertsonian translocations involve the long arm of acrocentric chromosomes with chromosomes13q;4q being predominantly involved. this defect can be transmitted along several generations, giving rise to chromosomally abnormal products with complete aneuploidy. it is unusual to observe this type of mutation associated with another chromosomal anomaly involving chromosome 21. the objective of this study was to describe the case of a newborn with down's syndrome (regular trisomy 21) associated with a 13q;14q robertsonian translocation. case report. we report the case of a newborn male who was the product of a twin pregnancy. at birth, the newborn demonstrated the following: absent moro's reflex, brachicephaly, slating ocular fissures, depressed nasal bridge, low-set ears, short neck, transverse palmar crease, clinodactyly of the fifth finger, right testicle undescended, and a heart murmur. chromosomal study revealed 46.xy, t(13;14) (q10;q10), +21. cytogenetic analysis of the family revealed in the mother (ii-1) 45,xx, t(13;14) (q10;q10), the father (ii-2) 46,xy; the mother's brother (ii-3) 46,xy; the newborn's older sister (iii-1) 46,xx; twin brother 45,xy, t(13;14) (q10;q10). conclusions. this was an unusual case of the association of down's syndrome with a balanced robertsonian translocation of chromosome 13;14 maternally transmitted.