With the mapping of human genes a wide open field has been laid open for accurate diagnosis of various cancers and other congenital malformations, maybe for other diseases also the nature of which so far has eluded the investigators.
Not only a deficiency or defect in chromosomes occurring in a particular individual suffering from cancer can be helpful in its diagnosis, but in certain conditions investigating for similar chromosomal defect in close family members one may also be able to identify those who are at risk to develop similar cancer in due course of time.
Those who are identified can be put on surveillance and for early detection of cancer and treatment at initial stages of disease with high chance of cure. Such a family with childhood cancer of kidney has been reported from St. Jude's Hospital at Memphis, Tennessee, USA.
A girl of Pakistani origin had been seeking advice for excessive obese build since early childhood without any relief, after seeking advice at the various famous centers overseas without relief, till finally on Cytogenetic testing she was found to be suffering from Prader Willie Syndrome. She did respond to the appropriate treatment due to accurate diagnosis. Cytogenetic testing is now recommended as a routine investigation for the commonest type of blood cancer (Leukemia) in children.
Though many in Pakistan are now familiar with imaging diagnostic tools like Ultrasound, C.T. Scan and MRI, very few know about Cytogenetics as a diagnostic tool. Facilities for this investigation are available only in a couple of centres, unfortunately none in public sector institutions where bulk of congenital malformations and childhood cancers are seen and treated. These conditions occur more commonly in poor families with large child population.
In clinical Cytogenetics, a specimen either of blood sample or tissues obtained during operation are treated to set up tissue culture. At the optimum time when the cells are dividing (mitosis) are fixed. The cell division itself is a normal process in order to replace depleted cells in the body and form tissues.
In these dividing cells, obtained from culture after fixation, Cytogenetist examines the chromosomes. Once the chromosomes are identified and studied they are imaged and karyotyped, meaning that the chromosomes are cut out and arranged or matched up to form all 23 pairs clearly identifying each one and how it compares with other. As all 46 chromosomes are lined up next to each other, it is much easier to determine if one of them is abnormal. This technology is commonly called G -banding.
Addition to the conventional above method of examining the chromosomes is the FISH (Fluorescent in situ Hybridisation) technique that has been more useful in detecting abnormalities not detected by G-banding. This technique detects the presence, or absence, of genes or even the rearrangement of one or more genes simultaneously. Often times, cultures do not need to be established to perform this test, which can yield better turnaround time. However, it is always recommended to perform routine Cytogenetics in conjunction with FISH.
A normal individual has 46 chromosomes in all cells in the body, except the red blood cells, which have none, and germ or sex cells, which have 23. Through magnification of microscope the Cytogenetist looks for unusual pattern I the chromosome structure or even complete gains and/ or loses whole of chromosomes (ie Trisomy 21, which causes Dawns syndrome or Monosomy X, which causes Turner syndrome.
There are two main types of chromosome studies. Constitutional chromosome studies, which are studies to rule out a chromosome abnormality someone is born with; and Neoplastic or cancerous chromosome studies to rule out an acquired abnormality.
Constitutional studies are required for conditions like mental retardation, various types of developmental delays, body dysmorphism, family history of chromosomal abnormality, multiple miscarriage and reproductive problems. Pre-natal studies in fetus are advised in case of advanced maternal age, abnormal bio-chemicals or triple screen, abnormalities found on ultrasound and birth of previous child with or family history of chromosome abnormality.
While testing for malignancy Cytogenetic plays an important role in detecting translocation in hematological malignancies. In about 50 percent blood cancer somatically acquired chromosomal translocation activates proto-oncogenes, which in turn disrupt the balance of proliferation, cell maturation and cell death. These chromosomal translocations in many cases fuse sequences of receptor TK gene to unrelated genes, resulting in chimeric protein with oncogenes properties. Majority of chromosomal translocation induced hematopiotic neoplasm restricted to single lineage arrested at a particular development stage of maturation depending upon the acquisition of the mutation. Occasionally more than one lineage or developmental stage is affected as in Lymphoid Leukemia.
In 1999 WHO published its new classification of Hematological malignancies that stratifies neoplasms primarily according to lineage. With each category, they are further defined by combination of morphology, immunophenotyping, Cytogenetics and clinical information. The cell of 'origin' in this classification is defined as the presenting cell phenotype.
'Child Aid Association', which is working for better treatment facilities for the poor sick children at the National Institute of Child Health, Karachi for past 27 years has realised the importance of Cytogentics as it is supporting the Pediatric Oncology Unit at the same institute since 1999 (which then Child Aid Association has the honour of establishing). On an average 180 children receive free treatment for various types of cancer every month, 50 percent suffering from Leukemia. Now Cytogenetic testing is performed for nearly all blood, lymphoid and solid tumours.
Blood cancer is the most common childhood cancer and more than 80 percent are Acute Lymphobalstic Leukemia, majority Pre-B ALL. The cure rates in developed countries are 75-80 percent. The exact incidence and survival rate in Pakistan still needs to be determined and standardisation of treatment protocols have to be enforced for desired outcome.
In December 2005 the project of establishing the Cytogenetics at the NICH was launched with the co-operation of the Director NICH, The Child Aid Association (CAA), The Association of the Pakistani Physicians of North America (APPNA) and Department of Cytogenetics at the Texas Children Hospital, Houston, Texas, USA. A lady MNA from Karachi, Ms Afsar Khanum, has kindly donated Rs 1.6 million for the construction of the building to house the Lab at the NICH.
The building is in the final stages of finishing and it is expected that the laboratory to be functional by the end of this year. The CAA from its own funds sent a technologist for training at the Royal Marsden Hospital, London, as trained personnel are not available in this field. It is expected that this service shall be open not only to the patients of NICH but all institutions in the province of Sindh and Balochistan. It will also be the training center for the Cytogenetics where doctors and technologists will get a chance to learn this new technique.
(Dr Rizwan C Naeem is Director, Cytogenetics at Texas children hospital, Houston, and Professor Nizamul Hasan is President of Child aid Association, NICH, Karachi.)