Clinical manifestations in trisomy 9.

Complete trisomy 9 is a lethal diagnosis and most fetuses diagnosed thus die prenatally or during the early postnatal period and majority of such cases have been known to end in spontaneous abortion in the first trimester itself. One such rare survival of fetus ending in normal delivery and surviving until 20 days is reported here detailing the clinical manifestations of the child during the period of survival. The salient clinical features observed were small face, wide fontanel, prominent occiput, micrognathia, low set ears, upslanting palpebral fissures, high arched palate, short sternum, overlapping fingers, limited hip abduction, rocker bottom feet, heart murmurs and also webbed neck, characteristic of this trisomy 9 syndrome.

Malignancies in Down syndrome.

Down Syndrome (DS) is associated with an increased incidence of malignancies, especially leukaemias. We came across 8 DS children presenting with malignancies and having trisomy 21 as the sole cytogenetic abnormality. Of these 8 DS cases, 4 presented with acute lymphocytic leukaemia, 2 with acute myeloid leukaemia and one case each with Hodgkin's disease and Wilms' tumour. There are contradictory reports regarding the distribution of myeloid versus lymphoid malignancies in DS children and their response to therapy. The exact mechanism by which patients with DS are predisposed to develop malignancies is unclear. However, presence of the extra chromosome no. 21 is presumed to disrupt the genetic balance which increases generalized susceptibility to genetic and environmental trauma. Furthermore, an increased methotrexate toxicity observed in these patients should also be taken into consideration in designing treatment for DS children with malignancies.

Molecular pathogenesis of chronic myelogenous leukaemia.

Chronic myelogenous leukaemia is a clonal neoplasm of the pluripotent haematopoietic stem cell which is characterized in most patients by a consistent cytogenetic abnormality known as the Philadelphia chromosome. This chromosome occurs as a consequence of a reciprocal translocation between the long arms of chromosomes 9 and 22 which results in the creation of a new gene comprising sequences from the c-abl gene on chromosome 9 and the bcr gene on chromosome 22. The protein encoded by this structurally altered hybrid gene differs from the normal c-abl gene product in both molecular weight and in tyrosine kinase activity. It is likely that these alterations in the c-abl gene product play a central role in the pathogenesis of this leukaemia.

Molecular cytogenetics of human cancer.

Cancer may arise from the genetic transformation of a single precursor cell, which proliferates to form a clone. Chromosomal abnormalities are associated with many types of tumours. Some of the chromosomal rearrangements such as translocation, deletion and insertion involve breakage of chromosomes close to known oncogenes. The close linkage between the chromosomal changes, the gene modifications and consequently altered protein function seen in malignant cells suggest that cancer is a genetic disease. Analysis of chromosomal abnormalities and oncogene amplifications in malignant cells have been found to be related to their malignant potential and hence may be utilized in the clinical management of patients with cancer.