Gene Mapping: Basics, Techniques and Significance.

Watson says, "Like the system of interstate highways spanning our country, the map of the human genome will be completed stretch by stretch". It may be possible to use genetic information to diagnose the disease accurately and to predict a patient's likely response to a particular medicine or treatment. For whole genome mapping development and application of mapping, sequencing and computational tools are very essential and also linkage, physical and sequence maps are required to put the information together. For most genome mapping projects involve markers consisting of a unique site in the genome and should be independent of any particular experimental resource. For mapping purpose the DNA and RNA identification is essential. These genes are identified by hybridizing DNA clones against Northern blot, cDNA libraries, Zoo blot, Western blot and Southern blot of genomic DNA digested with rare cutter restriction endonuclease. The various experimental studies of gene mapping have extended our understanding of the genetics. This has allowed the investigators to detect a particular gene, which is responsible for the disease. Recent studies have shown the various effective and scientific gene mapping techniques and gene identification methods, which are helpful to diagnose a particular disease. It is easy for the doctor to give right medicine to the right patient to cure the disease when he can identify the defective gene responsible for disease. This article reviews the details of identification techniques of genes, gene mapping with broad applications.

Assessment of HER-2/neu status in breast cancer using fluorescence in situ hybridization & immunohistochemistry: Experience of a tertiary cancer referral centre in India.

Background & objective: Determination of HER2 status in breast cancer has become important to identify potential candidates for anti-HER2 therapy. In this study we compared fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) for the determination of HER2 status in breast cancer patients referred to a tertiary care referral centre. Methods: A total of 200 cases of invasive breast cancer were evaluated for HER2 status using IHC and FISH and results were compared. Results: The IHC 3+ (93.9%) and IHC negative (85.9%) cases showed good concordance with the corresponding FISH results; while 66.6 per cent of IHC 2+ cases showed gene amplification by FISH. In addition, hormone receptor expression and HER2 gene status showed a statistically significant inverse association (P<0.05). Interpretation & conclusion: These findings reaffirm IHC as a prudent first-step to screen tissue samples for HER2 status and to determine suitability for technically demanding FISH test and the dual coloured FISH as a gold standard for determination of HER2/neu status in IHC equivocal cases of breast carcinoma.

Preliminary data of preimplantation genetic diagnosis for aneuploidy screening using fluorescent in situ hybridization in Siriraj Hospital.

Objective: Preimplantation genetic diagnosis (PGD) is technique for detecting genetic diseases. Preimplantation genetic diagnosis for aneuploidy screening (PGD-AS) using fluorescent in situ hybridization (FISH) has been used worldwide including at Siriraj Hospital. The objective of this study was to comparethe pregnancy rate between a PGD-AS group with standard assisted reproductive techniques (ARTs) in Siriraj Hospital. Methods: Couples who requested PGD-AS underwent a standard ARTs process followed with blastomere biopsy for FISH analysis. The pregnancy rate was compared among the PGD-AS group and the control group. The control group was divided into 2 subgroups – all patients required ARTs subgroup and age ≥ 35 yrs. subgroup. Results: 6 stimulated cycles from 4 patients were performed in the PGD-AS group. The pregnancy rate per stimulated cycle in the PGD-AS group, control group and age ≥ 35 yrs group were 33.33%, 16.20% and 12.05% respectively. Moreover, the pregnancy rate per transferred cycles in the PGD-AS group, control group and age ≥ 35 yrs group were 40.00%, 21.02% and 13.17% respectively. Conclusion: PGD is an advanced method for detecting genetic defects. PGA-AS might increase the pregnancy rate.

Physical mapping of the 18S and 5S ribosomal genes in nine Characidae species (Teleostei, Characiformes)

Characidae is one of the largest fish families of the Neotropical region, and presenting a pronounced morphological variability, certainly does not constitute a monophyletic group. The cytogenetical data also show a large chromosomal variation and can provide important information for a better understanding of the relationships between the species of this group. 18S and 5S rDNA probes were used in the present study for the chromosomal mapping in different Characidae species from the São Francisco River (Astyanax lacustris, Astyanax scabripinnis, Hasemania nana, Piabina argentea, Orthospinus franciscensis, Serrapinnus heterodon, Serrapinnus piaba and Myleus micans) and Alto Paraná (Astyanax altiparanae) basins. Species with a single pair of chromosomes bearing the nucleolar organizing regions (NORs) were identified, as well as species with multiple NORs, up to a maximum of seven 18S rDNA sites. The number of 5S rDNA site was also not constant, varying from two to eight. The mapping of the ribosomal genes was useful for the characterization and differentiation of the analyzed species.

A Case of 2q+ Syndrome Identified by Fluorescent In Situ Hybridization

We experienced a case of 2q+ syndrome in a neonate who had multiple congenital anomalies of long philtrum, a bow-shaped mouth, long fingers, and its second and fifth fingers overlapped with the third and the fourth. In the cytogenetic studies using G banding technique, an extra band of the distal long arm of chromosome 2 was shown. Because its extra chromosomal segment was too small and the parents' chromosome were normal, it was difficult to determine the origin of the additional segment. We could find the fluorescent signal from the extra chromosomal segment by using painting probe of chromosome 2. The karyotype of the patient was confirmed as 46, XX, 2q+. We reported the case with the review of the associated literatures.

A Case of 2q+ Syndrome Identified by Fluorescent In Situ Hybridization

We experienced a case of 2q+ syndrome in a neonate who had multiple congenital anomalies of long philtrum, a bow-shaped mouth, long fingers, and its second and fifth fingers overlapped with the third and the fourth. In the cytogenetic studies using G banding technique, an extra band of the distal long arm of chromosome 2 was shown. Because its extra chromosomal segment was too small and the parents' chromosome were normal, it was difficult to determine the origin of the additional segment. We could find the fluorescent signal from the extra chromosomal segment by using painting probe of chromosome 2. The karyotype of the patient was confirmed as 46, XX, 2q+. We reported the case with the review of the associated literatures.