Cytogenetic and molecular studies of an X;21 translocation previously diagnosed as complete monosomy 21.
We studied a child with apparent monosomy of chromosome 21. Cytogenetic, FISH and microsatellite analyses revealed a 45,X,-21,+der(X)t(X;21)(q25;q21.1) karyotype resulting from a de novo, unbalanced, X;21 non-reciprocal translocation of paternal origin, with partial monosomy of chromosomes 21 and X. An extreme, skewed X-inactivation pattern of the der(X) chromosome was demonstrated. Skewed inactivation probably accounted for a mild phenotype with respect to Xq25-->qter deletion while propagation of inactivation to the adjacent 21q region may account for mild clinical features associated to distal 21q monosomy.
Cardoso
Leila C A
LC
Genetics Division, Instituto Nacional de Câncer, Rio de Janeiro, Brazil.
Moraes
Lúcia
L
Camilo
Maria Jesus E
MJ
Mulatinho
Milene V
MV
Ramos
Hilda
H
Almeida
José Carlos C
JC
Llerena
Juan C
JC
Seuánez
Héctor N
HN
Vargas
Fernando R
FR
D002675:Child, Preschool; D002891:Chromosomes, Human, Pair 21; D041321:Chromosomes, Human, X; D005260:Female; D018392:Genomic Imprinting; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D009006:Monosomy; D014178:Translocation, Genetic; D049951:X Chromosome Inactivation