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05/02/2023 1
Genetic Counseling
: OLAGBAYE, Babakayode Abel
Dept of AnatomyUniversity of Ilorin, Ilorin
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We shall be discussing...What are involved
in Genetic counselling
Basic classification of
genetic disorders
Molecular basis of some of the
disorders
Different Approaches to
Genetic Counselling
Some gene testing Options
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What is Genetic Counselling?
• Medical education of affected individuals, individuals at the risk of being affected and/or the general public concerning inherited disorder.
• Genetics counselors are health care professionals with specialized graduate degrees and experience in medical genetics and counseling.
Elements of the practice of geneticcounselling include:
• 1- Assessment of the chance for recurrence or occurrence of a condition, after information gathering and establishing or verifying the diagnosis
• 2- Education about inheritance; natural history, testing options, medical management, prevention, social support and research.
• 3-Counseling and psychological support to help clients adapt to their situation and choices
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CLASSIFICATION OF GENETIC DISORDERSThey are of 3 types:
1.Chromosomal abnormalities; Klinefilter syndrome, Turners syndrome philadephia
chromosome…
2.Mendelian diseases; Dominant, Recessive, Sex linked diseases
3.Multifactorial disorders; Hypertension, Schizophrenia, Diabetes, Congenital heart disease
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47, XXY or 48,XXXY sex chromosome
Features;• Cryptorchidism; undescent testes
• Seminiferous tubule dysgenesis resulting in azospermia and infertility
• Gynecomastia; breast enlargement reduced facial and body hair
Molecular Changesapproximately 48% are due to meiosis I errors, 29% to meiosis II errors,7% to meiotic origins and 16% to postzygotic mitotic errors. (Thomas et al., 2000)
Klinefilter syndrome
Credit: Alila Medical Media/Shutterstock.com
Turner SyndromeWhen one normal X chromosome Is
present in a female's cells And the other sex chromosome is missing or structurally altered
FEATURES• Ovarian hypo-function or failure • 30% have Webbed neck• Lymphedema (puffiness)• Skeletal abnormalities (short)• Heart defects (carctation of the
aorta)
Molecular basis non-disjunction (in meiosis)Some genes identified by Chu & Conor (1995): XE7, MIC2 which encodes a glycoprotein involved in T cell
adhesionZFX/ZFY which encodes a zinc finger protein. In rare cases caused by a partial deletion of the X(SHOXgene) (Frühmesser, 2011) 05/02/2023 7
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Philadephia ChromosomeIts a translocation where parts of
two chromosomes, 9&22, swap places.
A fusion gene is created by juxtaposing the ABL1 gene on chromosome 9(regionq34) to a part of BCR gene on chromosome 22 (region q11) containing a fusion gene BCR-ABL1
Features• Acute lymphoblastic Leukaemia• Chronic myeloid leukaemia
Downloaded from http://adc.bmj.com/ on January 31, 2017 - Published by group.bmj.com
Shortened 22,
longer 9.
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Approaches to GENETIC COUNSELING
They are of 2 types:
1.Prospective approach2.Retrospective approach
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Prospective(preventive) genetic counselling:
This approach requires
Identifying heterozygous individuals for any particular defect by screening
Explaining to them the risk of their having affected children if they marry another heterozygote for the same gene.
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Still PREVENTIVE AND SOCIAL MEASURES• EUGENICS: (i) Negative eugenics
AIM: To reduce the frequency of hereditary disease and disability in the community to as low as possible
(ii)POSITIVE EUGENICS:AIM: To improve the genetic composition of the population by encouraging carriers of desirable genotypes.
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OTHER GENETIC PREVENTIVE MEASURES
1.CONSANGUINEOUS MARRIAGES;When blood relatives marry each other there is an increased riskin the offspring of traits controlled by recessive genes and thosedetermined by polygenes
.Eg: Albinism, Phenylketonuria…
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2.LATE MARRIAGES:
Trisomy or mongolism is more frequent in children born of elderly mothers.Hence early marriage of females is better than late marriage from the point of view of preventing mongolism.
(US dept. of health and human services, 2017)
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Retrospective (Curative) Genetic Counseling
The methods which could be suggested underretrospective genetic counseling are:
1.Contraception2.Pregnancy termination.3. Sterilization4. Gene therapy where feasible
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• EUTHENICS: This involves environmental manipulation to
improve the livelihood of patience affected Studies with mentally retarded children
indicated that exposure to environmental stimulation improved their IQ.
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EARLY DIAGNOSIS:
1.DETECTION OF GENETIC CARRIERS :
It is possible to identify the healthy carriers of a number of genetic disorders, especially the inborn errors of metabolism using gene testing.
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INDICATION for PRENATAL DIAGNOSIS:
- Advanced maternal age- Previous child with chromosome aberration- Intrauterine growth delay- Biochemical disorders- Congenital anomaly
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3.SCREENING OF NEWBORN INFANTS:
Screening tests for early diagnosis of :
- chromosome abnormalities- congenital dislocation of hip- congenital hypothyroidism - sickle cell disease- cystic fibrosis
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Testing Options
• Karyotype • Aminocentesis
Involves taking a sample of the amniotic fluid from the uterus
•Blood sample collection•A bone marrow biopsy•placenta
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Testing Options
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Pedigree Analysis- checking family history
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When to see a Genetics Counselor
• Genetic counseling can have the greatest impact when individuals or couples at genetic risk are identified, before they have developed symptoms themselves or produced their first affected child.
• But even after pregnancy, a meeting with a genetic counselor can still be helpful.
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REFERENCE
1. TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE; 23rd Edition (2015) by PARK 2. Chu and Connor (1995); Molecular biology of Turners syndrome; Archives of Disease in
Childhood; 72: 285-286 Downloaded from http://adc.bmj.com/ on January 31, 2017 - Published by group.bmj.com
3. http://www.ornl.gov/sci/techresources/Human_Genome/medicine/genecounseling.shtml
4. http://geneticcounseling.genetics.utah.edu/
5. US dept. of health and human services; klinefelter syndrome published Jan 17; 2017. Accessed on 24 Jan, 2017 from https://ghr.nlm.nih.gov/condition/klinefelter-syndrome
6. Frühmesser A, Kotzot D. (2011) Chromosomal variants in klinefelter syndrome. Sex Dev.;5(3):109 23. doi: 10.1159/000327324. Epub 2011 Apr 29. Review. Citation on PubMed
7. Thomas NS, Collins AR, Hassold TJ, Jacobs PA (2000); A reinvestigation of non-disjunction resulting in 47, XXY males of paternal origin. Eur J Hum Genet; 8:805–808. | Article | PubMed | ISI | ChemPort |
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