Familial small supernumerary marker chromosome (sSMC) (14)(:p11-q11:) in a child with translocation down syndrome.

We report a case of familial small supernumerary marker chromosome (sSMC) in a child with translocation Down syndrome (DS)and mother.The GTG-banded chromosomal analysis of DS child revealed 47,XY,+21,+mar and mother karyotype was 47,XX,+mar.The GTG-banded sSMC had a similar morphology of small acrocentric chromosomes .Fluorescence in situ hybridization (FISH)evaluation of sSMC using centromere probes(13/21,14/22,22)confirmed sSMC as derivative chromosome 14.The sSMC was not specifically stained with whole chromosome paint and arm-specific probes for chromosome 14;thus it has been described as der(14)(:p11-q11:).The phenotypic changes were not evident, may be due to trisomy condition in the child or the sSMC contain repetitive sequences.

Chromosomal breakage in myelodysplatic syndrome.

The myelodysplastic syndrome (MDS) represents a group of clonal hematological disorders characterized by progressive cytopenia reflecting defects in erythroid, myeloid and mega karyocytic maturation. The incidence of MDS is greter in older age groups. Detailed studies on MDS from India are not available. Cytogenetic study using GTG-banding and FISH revealed 54.5% clonal chromosomal abnormalities. We have carried out chromosomal breakage study from peripheral blood cultures induced with mitomycin C, in karyotypically normal MDS (49) and 15 (30.6%) showed significant (p < 0.001) increase in chromosome damage compared to controls. Among 22 occupationally exposed MDS, 6 (27.3%) showed a high frequency of chromosome breakage while in the non-exposure (n=27) group, high chromosome breakage was noted in 9 (33.3% ) MDS patients. Our results suggest that the high chromosome damage may be due to acquired Fanconi anemia which leads to multiple defects in chromosomes and clonal chromosome anomalies.

Dandy-Walker malformations in a case of partial trisomy 9p (p12.1→pter) due to maternal translocation t(9;12)(p12.1;p13.3).

We describe a five-year-old proband presented with Dandy-Walker malformations, right microopthalmia, hamstring contractures, undescended testis with absence of testis in right scrotum in addition to typical trisomy 9p clinical features. Routine cytogenetic studies with GTG - banding showed 46,XY,der(12)t(9;12) (p12;q13.3),mat karyotype (trisomy 9p). Chromosomal analysis of the father was normal and phenotypically normal mother had 46,XX,t(9;12)(p12;q13) karyotype. Fluorescence in situ hybridization analysis with single copy probes bA5OIA2 (9p11.2), bA562M8 (12p12.1) and centromere probes (9) showed break point at 9p12.1 region. The gene dosage effect of Chromosome 9p along with environmental factors might be associated with Dandy- Walker malformations in the patient.

Pericentric inversion of chromosome 9[inv(9)(p12q13)]: Its association with genetic diseases.

Background: The chromosomal polymorphism of short arms of acrocentric chromosomes and heterochromatin variation of Chromosomes 1, 9, 16 and Y have been reported in humans. The pericentric inversion of Chromosome 9 is commonly seen in normal humans and the frequency estimated to be 1 to 3% in general population and inherited in mendalian fashion or might occur spontaneously without any clinical significance. Aim: The aim of the study was to study the frequency of inv(9) and its clinical correlation with human genetic diseases. Materials and Methods:0 The chromosomal analysis using GTG-banding was carried out in 3,392 cases suspected with genetic diseases. Results: The pericentric inversion frequency of different chromosomes in our study was 1.24% and frequency of inv(9)(p12q13) was high (64.29%) compared to other pericentric inversions in our study. A high frequency (9.33%) of inv(9)(p12q13) was detected in children with dysmorphic features and congenital anomalies. Conclusion: As a high frequency of inv(9)(p12q13) detected in children with dysmorphic features, the inv(9) definitely have a role in the abnormal phenotype development. During inversion event there might be loss or suppression of euchromatin chromosome region and hence detailed chromosomal break point study is important to understand the clinical significance of the pericentric inversion of Chromosome 9.