05/02/2023 1

Genetic Counseling

: OLAGBAYE, Babakayode Abel

Dept of AnatomyUniversity of Ilorin, Ilorin

05/02/2023 2

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

05/02/2023 3

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

05/02/2023 5

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

05/02/2023 6

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

05/02/2023 8

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.

05/02/2023 9

Approaches to GENETIC COUNSELING

They are of 2 types:

1.Prospective approach2.Retrospective approach

05/02/2023 10

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.

05/02/2023 11

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.

05/02/2023 12

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…

05/02/2023 13

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)

05/02/2023 14

Retrospective (Curative) Genetic Counseling

The methods which could be suggested underretrospective genetic counseling are:

1.Contraception2.Pregnancy termination.3. Sterilization4. Gene therapy where feasible

05/02/2023 15

• 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.

05/02/2023 16

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.

05/02/2023 17

INDICATION for PRENATAL DIAGNOSIS:

- Advanced maternal age- Previous child with chromosome aberration- Intrauterine growth delay- Biochemical disorders- Congenital anomaly

05/02/2023 18

3.SCREENING OF NEWBORN INFANTS:

Screening tests for early diagnosis of :

- chromosome abnormalities- congenital dislocation of hip- congenital hypothyroidism - sickle cell disease- cystic fibrosis

05/02/2023 19

Testing Options

• Karyotype • Aminocentesis

Involves taking a sample of the amniotic fluid from the uterus

•Blood sample collection•A bone marrow biopsy•placenta

05/02/2023

Testing Options

20

Pedigree Analysis- checking family history

05/02/2023 21

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.

05/02/2023 22

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 |

23