Diagnosis of cryptic chromosomal syndromes by fluorescence in situ hybridization (FISH)

Overview of Clinical Cytogenetics

Chromosome analysis is one of the first approaches to genetic testing and remains a key component of genetic analysis of constitutional and somatic genetic disorders. Numerical or unbalanced structural chromosome abnormalities usually lead to multiple congenital anomalies. Sometimes these are compatible with live birth, usually resulting in severe cognitive and physical handicaps; other times they result in miscarriage or stillbirth. Chromosome rearrangements also occur as somatic changes in malignancies. Identification of constitutional chromosomal anomalies (anomalies present in most or all cells of the body and/or the germline) can provide important information for genetic counseling. In this unit, we introduce chromosomal microarray analysis (CMA), which is a relatively recent addition to cytogenetic technologies, and has become the recommended first-tier testing method for patients with developmental delay, intellectual disability, autism, and/or multiple congenital anomalies. We also discuss non-invasive prenatal testing/screening (NIPTS), which uses circulating cell-free fetal DNA (cfDNA) from maternal plasma to rapidly screen for autosomal and sex-chromosome aneuploidies. Cytogenetic analysis of tumors is helpful in diagnosis and in monitoring the effects of treatment. The protocols in this chapter cover the clinical study of chromosomes in nonmalignant tissues.

Molecular cytogenetic analysis of telomere rearrangements

Genomic imbalances involving the telomeric regions of human chromosomes, which contain the highest gene concentration in the genome, are proposed to have severe phenotypic consequences. For this reason, it is important to identify telomere rearrangements and assess their contribution to human pathology. This unit describes the structure and function of human telomeres and outlines several methodologies that can be employed to study these unique regions of human chromosomes. It is a revision of the original version of the unit published in 2000, now including an introductory section describing advances in the discipline that have taken place since the original publication.