Cytogenetic and molecular evaluation of 241 small supernumerary marker chromosomes: cooperative study of 19 Italian laboratories.
OBJECTIVE
We evaluated the experiences of 19 Italian laboratories concerning 241 small supernumerary marker chromosomes (sSMCs) with the aim of answering questions arising from their origin from any chromosome, their variable size and genetic content, and their impact on the carrier's phenotype.


METHODS
Conventional protocols were used to set up the cultures and chromosome preparations. Both commercial and homemade probes were used for the fluorescent in situ hybridization analyses.


RESULTS
A total of 113 of the 241 sSMCs were detected antenatally, and 128 were detected postnatally. There were 52 inherited and 172 de novo cases. Abnormal phenotype was present in 137 cases (57%), 38 of which were antenatally diagnosed. A mosaic condition was observed in 87 cases (36%). In terms of morphology, monocentric and dicentric bisatellited marker chromosomes were the most common, followed by monocentric rings and short-arm isochromosomes. The chromosomes generating the sSMCs were acrocentric in 132 cases (69%) and non-acrocentric chromosomes in 60 cases (31%); a neocentromere was hypothesized in three cases involving chromosomes 6, 8, and 15.


CONCLUSIONS
The presented and published data still do not allow any definite conclusions to be drawn concerning karyotype-phenotype correlations. Only concerted efforts to characterize molecularly the sSMCs associated or not with a clinical phenotype can yield results suitable for addressing karyotype-phenotype correlations in support of genetic counseling.
Dalprà
Leda
L
Department of Experimental, Environmental Medicine, University Milan-Bicocca, Monza, Italy.
Giardino
Daniela
D
Finelli
Palma
P
Corti
Cecilia
C
Valtorta
Chiara
C
Guerneri
Silvana
S
Ilardi
Patrizia
P
Fortuna
Renato
R
Coviello
Domenico
D
Nocera
Gianfranco
G
Amico
Francesco Paolo
FP
Martinoli
Emanuela
E
Sala
Elena
E
Villa
Nicoletta
N
Crosti
Francesca
F
Chiodo
Francamaria
F
di Cantogno
Ludovica Verdun
LV
Savin
Elisa
E
Croci
Gianfranco
G
Franchi
Fabrizia
F
Venti
Giovanna
G
Donti
Emilio
E
Migliori
Valeria
V
Pettinari
Antonella
A
Bonifacio
Stefania
S
Centrone
Claudia
C
Torricelli
Francesca
F
Rossi
Simona
S
Simi
Paolo
P
Granata
Paola
P
Casalone
Rosario
R
Lenzini
Elisabetta
E
Artifoni
Lina
L
Pecile
Vanna
V
Barlati
Sergio
S
Bellotti
Daniela
D
Caufin
Daniele
D
Police
Adalgisa
A
Cavani
Simona
S
Piombo
Giuseppe
G
Pierluigi
Mauro
M
Larizza
Lidia
L
D002869:Chromosome Aberrations; D005820:Genetic Testing / Q000379:methods*; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D040582:Inheritance Patterns / Q000235:genetics; D007558:Italy; D010641:Phenotype