GIM 201 Lesson 5 - Cytogenetics PDF

Chromosomes, Karyotyping, and Chromosomal Abnormalities Learning Outcomes By the end of this session, you should be able to: Describe the morphology and terminology of chromosomes. Examining the chromosome > and its use in identifying...

Chromosomes, Karyotyping, and Chromosomal Abnormalities Learning Outcomes By the end of this session, you should be able to: Describe the morphology and terminology of chromosomes. Examining the chromosome > and its use in identifying chromosomal Explain the concept of karyotyping - * too few chromosome many or abnormalities. Down trisonomy) syndrome - Classify chromosomal abnormalities (aneuploidy, polyploidy, structural abnormalities). Discuss the clinical significance of numerical and structural chromosomal abnormalities. Introduction to Chromosomes Thread-like structures made of DNA and proteins. 23 pairs of chromosomes in humans (46 in total). Chromosome structure: Centromere, telomere, p (petite) arm, q arm. Chromosomes carry genetic information essential for inheritance. - Cytogenetic analyses are almost always based on examination of chromosomes fixed during mitotic metaphase. * chromosomes are packed super During that phase of the cell cycle, DNA has been replicated and the chromatin is highly condensed. tightly to share DNA equally when cell divides The two daughter DNAs are encased in chromosomal proteins forming sister chromatids, which are held together at their centromere. The centromere is the primary constriction point that plays a crucial role in the movement of chromosomes => during cell division and is the attachment point for spindle fibres. &  is like belt Centromere = Chromosome Morphology Chromosomes vary in size, shape, and banding patterns. Karyotypes display chromosomes in pairs, organized by size and centromere position. Middle - Keytop features: Metacentric, top near the -> close to very submetacentric, acrocentric - very tip ~ at - and telocentric, depending on - location of centromere. O O 8 O ↓ ↓ Almost at slightly off M = middle Center Middle tip Tip  ⑪like taking family photo of chrome helps to find chromosomal problems that genetic 8 lining th cause ad disorder up to serifanything is extrao my ↓ Karyotyping: Definition and Process ~ Normal karyotype Karyotyping: an advanced genetic analysis technique used to - examine the chromosomal composition of an individual's cells. This method is critical for identifying and understanding chromosomal abnormalities that can lead to genetic disorders, impact fertility, and influence developmental processes. - Chromosomes are stained, for example with Giemsa stain, photographed, and arranged in pairs. Karyotyping helps identify chromosomal abnormalities like aneuploidy and structural changes. Extra or Fluorescence In Situ Hybridisation (FISH): Uses fluorescent8 missing chromosome ~entrichromoso probes to target specific chromosomes, detecting aneuploidies in specific cell populations. add glowing labels to chrom to spot specific problem , Array Comparative Genomic Hybridisation (aCGH): Measures DNA quantities to identify unbalanced chromosomal abnormalities across the genome.& Measures the DNA in drow : to find extra pieces missing or - Advanced Karyotyping Techniques Karyotyping is a multi-step process involving cell preparation, chromosome staining, and detailed analysis using microscopy. of 1. Sample Preparation: Cells, often derived from peripheral blood, amniotic fluid, or bone marrow, are cultured in media that stimulates cell division and arrested in metaphase where chromosomes are most -is ↑ M to visible. ↳ chromosomes are easy see. 2. Chromosome Harvesting and Staining: Cells are treated with a hypotonic solution to swell them, fixed in a solution of methanol and acetic acid, and then dropped onto slides to spread the chromosomes. The chromosomes are stained to produce distinct banding patterns for detailed analysis. 3. Microscopic Analysis and Imaging: Chromosomes are examined under a high-power microscope, and images are captured. Each chromosome is identified and arranged in a standard karyotype format based on size, banding pattern, and centromere position. - ① Grow cells ② Stop cell division at metaphase ③ stair chrom and take pic  Approaches to karyotyping – new and old In addition to classical Giemsa staining of chromosomes, fluorescence in situ hybridisation can be used to “paint” O chromosomes in different colours. Multiple probes are used for each chromosome, allowing us to generate a “spectral karyotype A supernumerary ring marker originating from chromosome 16. The sample - tested was amniotic fluid. Banded metaphase (left) and spectral karyotype (right) are shown. Marker origin was confirmed by FISH using a chromosome 16 centromeric probe (not shown).  Spectral karyotyping highlights genomic alterations in cancer ↓ translocation from metaphase from a cancer patient : Numerical Chromosomal Abnormalities Aneuploidy: An abnormal number of chromosomes (e.g., trisomy or monosomy). Trisomy: Presence of an extra chromosome (e.g., Down’s syndrome, =21). O trisomy = 3 copiesTof chromosome 21 - -1 missing Monosomy: Missing a chromosome (e.g., Turner’s syndrome,C monosomy - => X). Missing Only one X chromosome Polyploidy: More than two sets of chromosomes (rare in humans). = =>  = 4 types Structural Chromosomal Abnormalities Structural abnormalities include L & deletions, (12) duplications, translocations, and inversions. S Deletions: A portion of the chromosome is missing. Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material. Translocations: A segment of one chromosome is transferred to another. e HSR = homogenously stained region – multiple repeats of 100-200bp Double minutes = extrachromosomal amplifications t = - loss of heterozygote  abnormalities. Chromosomal aberrations -  - important Clinical Implications of Chromosomal Abnormalities ① ⑧ Chromosomal abnormalities can lead to developmental - delays, intellectual disability, and ③ increased risk of cancers. - - - ⑨ Early diagnosis through-karyotyping and genetic testing is critical for management and treatment. - Karyotyping in Clinical Practice - ⑧ ⑤ Karyotyping is used in prenatal screening, cancer diagnosis, and infertility evaluations. - - Abnormal karyotypes can guide treatment decisions, genetic counseling, and family planning. -- - Detection and Diagnostic Techniques: (+ 2 sets) Ultrasound: Early detection of physical anomalies suggestive of polyploidy conditions. Karyotyping and FISH: For definitive diagnosis, particularly useful in prenatal testing. Quantitative Fluorescent PCR (QF-PCR): For rapid detection of common O - aneuploidies and some polyploidies, focusing on specific chromosome numbers. abnormal no · ofchrome  Aneuploidy Aneuploidy is a chromosomal variation characterised by an abnormal number of chromosomes, diverging from a complete set. ⑳u It results from errors in the segregation process during meiosis or mitosis, typically during anaphase when chromosomes or chromatids fail to separate properly. This results in gametes or cells with extra or missing chromosomes. Causes and Processes: Non-disjunction: The primary mechanism behind aneuploidy. During meiosis I, homologous chromosomes may= fail to separate, while in meiosis II or mitosis, sister chromatids may not segregate. This leads to gametes with n+1 or n-1 chromosomes, instead of the normal n. Anaphase Lag: A chromosome or chromatid fails to move to the spindle pole during cell division, leading to its loss in the daughter cells.  Types and Examples: Clinical Implications: u Monosomy: The loss of one chromosome (2n-1), The severity and type of symptoms depend with Turner syndrome (45,X) being the most on the specific chromosomes involved. prevalent example, where females have a single X Autosomal aneuploidies can be severe and chromosome. often lethal, whereas sex chromosome - Trisomy: The gain of an extra chromosome aneuploidies typically present milder (2n+1). Common examples include: phenotypes. i. Down Syndrome (Trisomy 21): Characterised Issues include developmental delays, by intellectual disability, distinct facial physical abnormalities, and increased features, and a higher risk of certain medical susceptibility to illnesses and metabolic conditions. disorders. ii. Patau Syndrome (Trisomy 13) and Edwards Syndrome (Trisomy 18): Both involve severe developmental issues and typically result in early death.  Polyploidy Types and Examples: Triploidy (3n): Often results from fertilisation of a normal oocyte by two sperm or by a diploid sperm Polyploidy refers to cells and organisms containing and is usually lethal in humans. more than two paired (homologous) sets of chromosomes. It is common in the plant kingdom Tetraploidy (4n): Arising from the failure of the first zygotic division, leading to doubling of the and certain animal taxa but rare and often non-viable chromosome number. in humans. Causes and Processes: Clinical Implications: Polyploid foetuses often miscarry, and if born, do not Failed Cytokinesis: After nuclear division, usually survive long due to multiple congenital cytokinesis might fail, resulting in a single cell anomalies and organ system failures. with duplicated DNA. Fertilisation Errors: Such as dispermy, where an Specific manifestations can include severe intellectual disabilities, growth retardation, and abnormal egg is fertilised by two sperm, or the fusion of a diploid gamete with a haploid gamete. physical features. Detailed Examination of Chromosomal Abnormalities Chromosomal abnormalities are generally categorized into numerical and structural types, each of which can have profound biological and clinical implications. Numerical Abnormalities: Aneuploidy: This occurs when an individual has one extra or one less chromosome than normal, examples include Trisomy 21 (Down syndrome) and Monosomy X (Turner syndrome). This typically results from nondisjunction, an error in chromosome separation during cell division. Polyploidy: A condition where a cell has more than two complete sets of chromosomes. It is rare in humans but can be seen in cases like triploidy. Structural Abnormalities: Translocations: This occurs when a segment of one chromosome dissociates and reattaches to a different chromosome. Types include reciprocal and Robertsonian translocations (1:1000 births), when long arm of the chromosome is translocated to short arm of partner chromosome – and can lead to evolutionary changes (eg humans have 46 chromosomes whereas great apes have 48 – with 2a and 2b) Deletions and Duplications: These are losses or gains of chromosome segments that can lead to various developmental and genetic disorders. Inversions: A chromosomal segment breaks off, inverts, and reattaches itself, which may disrupt gene function. Ring Chromosomes: These form when a chromosome’s end breaks and the arms fuse together to form a ring, often leading to severe genetic effects.  Case Study 1: Trisomy 21 (Down Syndrome) Trisomy 21, also known as Down syndrome, is one of the most prevalent chromosomal disorders worldwide, occurring in approximately 1 in every 700 births. It involves the presence of an extra copy of chromosome 21. Trisomy 21 typically results from non-disjunction during meiosis I in the mother, leading to the production of a gamete with an extra chromosome. This extra chromosome 21 is then passed on to the embryo, resulting in three copies of chromosome 21 in all cells. Clinical Manifestations: Distinctive facial features such as a flat face, small ears, slanted eyes, and a protruding tongue. Cognitive impairment ranging from mild to moderate. Increased risk of congenital heart defects, gastrointestinal blockages, and early-onset Alzheimer’s disease. Hypotonia (poor muscle tone) from birth. Diagnosis and Treatment: Prenatal screening includes nuchal translucency ultrasound and blood tests for maternal serum markers. Confirmatory diagnostic testing via amniocentesis or chorionic villus sampling (CVS) to analyse fetal chromosomes. No cure: treatment focuses on managing symptoms, including early intervention programs, special education, and health surveillance for associated conditions.  Case Study 2: Turner Syndrome (Monosomy X) Turner syndrome affects approximately 1 in 2,500 female live births and is characterised by the partial or complete absence of one X chromosome (45,X). The majority of cases result from non-disjunction during sperm or egg formation, leading to a zygote with only one X chromosome. In some cases, mosaicism may occur, where some cells have two X chromosomes, and others have one. Clinical Manifestations: Short stature, typically evident by about age 5. Lack of ovarian development leading to infertility and absence of menstruation. Congenital heart defects, particularly coarctation of the aorta. Neck abnormalities such as webbing and a low hairline. Diagnosis and Treatment: Diagnosis often occurs in adolescence due to delayed puberty or infertility issues. Karyotyping to confirm the absence of the second X chromosome. Hormone replacement therapy to promote development of secondary sexual characteristics. Regular cardiac monitoring and potential surgical interventions for heart defects.  Case Study 3: Trisomy 18 (Edwards Syndrome) Edwards syndrome, or Trisomy 18, is a severe chromosomal condition affecting about 1 in 6,000 live births. It is associated with a high rate of miscarriage and stillbirth. Like Down syndrome, this condition also results from non-disjunction, but involves chromosome 18. Most affected individuals have three copies of chromosome 18 in all of their cells. Clinical Manifestations: Severe intellectual disability and developmental delays. Structural heart defects and renal malformations. Abnormalities in other organs, leading to various health complications. Clenched hands with overlapping fingers, small jaw, and low-set ears. Diagnosis and Treatment: Prenatal detection via ultrasound showing multiple physical anomalies. Karyotype analysis post-birth or from prenatal testing like amniocentesis. Care is supportive and palliative, focusing on the comfort and quality of life, as many infants do not survive beyond the first year.  Case Study 4: Klinefelter Syndrome Klinefelter syndrome is one of the most common chromosomal disorders, affecting 1 in every 500 to 1,000 male newborns. It is typically characterised by a 47,XXY karyotype. This syndrome typically arises from non-disjunction during meiosis in one of the parents. An extra X chromosome is retained in the male child, leading to the XXY condition. This can occur either in maternal meiosis II or paternal meiosis I. Clinical Manifestations: Tall stature with disproportionately long arms and legs. Small, firm testes and reduced fertility. Gynecomastia (enlarged breast tissue) and reduced facial and body hair. Possible learning disabilities and delayed speech and language development. Diagnosis and Treatment: Diagnosis through hormone analysis and karyotyping. Testosterone replacement therapy from puberty to improve secondary sexual characteristics. Fertility treatment options, including assisted reproductive technologies.  1960 – Most patients with chronic myeloid Case Study 5: Chronic Myeloid Leukaemia (CML): leukemia have shortened chromosome 22, the i. Genetics: Caused by a translocation between Philadelphia chromosome chromosomes 9 and 22, producing the Philadelphia chromosome. ii. Clinical Features: Symptoms include fatigue, weight loss, and splenomegaly. iii. Management: Treated with targeted therapies like tyrosine kinase inhibitors. 1973 – Missing piece of chr 22 translocated to chr 9, a 9:22 translocation  Case Study 6: Cri-du-chat Syndrome Cri-du-chat syndrome is a rare genetic disorder due to a partial chromosome deletion on chromosome 5. Its name is a French term ("cat-cry" or "call of the cat") referring to the characteristic cat-like cry of affected children. The condition affects an estimated 1 in 50,000 live births across all ethnicities. Clinical Manifestations: feeding problems because of difficulty in swallowing and sucking; mutism; low birth weight and poor growth; severe cognitive, speech and motor disabilities; behavioural problems such as hyperactivity, aggression, outbursts and repetitive movements; unusual facial features, which may change over time; excessive drooling; small head (microcephaly) and jaw (micrognathism); widely-spaced eyes (hypertelorism); skin tags in front of ears. Diagnosis and Treatment: Diagnosis through distinctive cry and karyotyping. There is not a specific way to treat the condition as the brain damage caused by this condition occurs in the early stages of embryo development Prognosis is good if patients survive first few years Conclusion: Chromosomal changes can have dramatic phenotypes in patients Different approaches to karyotyping are important tools to help support diagnosis There are multiple ways in which chromosomes can be altered – with vastly different impacts on phenotype You need to be comfortable with the terms we have mentioned – aneuploidy, polyploidy, different types of translocation, loss of heterozygosity, deletion, duplication, inversion. There are a number of specific syndromes associated with specific chromosomal changes