[Characterization of marker chromosomes using molecular cytogenetic methods in patients with mental retardation and congenital malformations].
BACKGROUND
Until recently, great variety of marker chromosomes and difficulties with their identification have presented a problem for cytogenetic and clinical interpretation of the karyotype. At present, molecular cytogenetic methods of chromosome analysis enable precise characterization of such abnormalities providing knowledge necessary for estimation of their genetic risk.


OBJECTIVE
The aim of the study was molecular cytogenetic characterization of marker chromosomes recognized in three patients, an analysis of clinical features in relation to the abnormality and estimation of genetic risk of identified markers.


METHODS
Karyotypes of three phenotypically abnormal patients were estimated in lymphocytes from peripheral blood by G banding analysis. Marker chromosomes were identified by fluorescence in situ hybridization (FISH), multiplex FISH, multicolor band and high resolution comparative genomic hybridization methods.


RESULTS
Marker chromosomes were identified as inv dup(22)(pter->q11.2::q11.2->pter), der(8)(:p22->q11.2:), der(2l)(:pter->q21.3:) and der(19)(:p11->q13.1). All of them contained euchromatic sequences. First marker, an inverted duplication of chromosome 22q11.2 corresponding to tetrasomy of this chromosome region was recognized in a child with partial cat eye syndrome. Two further markers derived from chromosomes 8 and 21 were found in a child with mosaic karyotype and clinical features of trisomy 8p. In the third case additional chromosome material was derived from chromosome 19 and it was found in a patient with mild mental retardation and clinical features of ovary dysgenesis. Genetic risk of identified marker chromosomes except for mar(19) was estimated as high.


CONCLUSIONS
Our results provide further evidence for diagnostic value of molecular cytogenetic methods. They also confirmed the general opinion of the high risk of phenotypic abnormalities in the carriers of marker chromosomes containing euchromatic sequences.
Bocian
Ewa
E
Zakład Genetyki Medycznej, Instytut Matki i Dziecka, ul. Kasprzaka 17a, 01-211 Warszawa, Poland. ebocian@imid.med.pl
Nowakowska
Beata
B
Obersztyn
Ewa
E
Borg
Katarzyna
K
Chudoba
Ilse
I
Kostyk
Ewa
E
Kruczek
Anna
A
Pietrzyk
Jacek
J
Mazurczak
Tadeusz
T
D000015:Abnormalities, Multiple / Q000235:genetics*; D000782:Aneuploidy; D002675:Child, Preschool; D002877:Chromosomes, Human; D002888:Chromosomes, Human, Pair 19; D002891:Chromosomes, Human, Pair 21; D002892:Chromosomes, Human, Pair 22; D002898:Chromosomes, Human, Pair 8; D002658:Developmental Disabilities / Q000235:genetics; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D007223:Infant; D008607:Intellectual Disability / Q000235:genetics*; D007621:Karyotyping; D008297:Male