Medical Genetics

LECTURE 5Genetic Counseling

Objectives

1. To understand the principle steps of genetic counseling.

2. To know the ethical principles in performing genetic counseling.

3. To understand unique features of genetic counseling in Arabic/Islamic communities.

4. To know the sequence of steps for pre-marital screening.

Genetic Counselling

• Genetic disorders:• Chromosomal• Single gene• Multifactorial• Mitochondrial• Acquired somatic

• Only single disorders follow a clearly defined pedigree pattern of inheritance “Mendelian Pattern”.

• During genetic counselling it is essential to establish whether or not the disorder is Mendelian and to calculate the precise risk of recurrence.

Genetic Counselling for Mendelian Disorders

• Pattern of transmission judged from family tree. For several diseases the family tree may be

conclusive even if accurate diagnosis is not made.

• For some diseases pedigree pattern is not helpful and only clinical diagnosis is used

• For some disorders the pattern looks complicated and the exact diagnosis cannot be made.

• More common, a combination of clinical diagnosis and comparable pedigree pattern is required.

Establishment of Mendelian Inheritance

Essential Components of Genetic Counselling

Essential Components of Genetic Counselling

History and pedigree

construction

Clinical Examination

Confirmatorydiagnosis

Counselling

Availableoptions

Calculation ofrecurrence risk

Follow-up

- History findings- Clinical examination findings- Radiology findings- Laboratory parameter results- DNA studies results- Others

Recurrence Risk

ETHICAL PRINCIPLESETHICAL

PRINCIPLES

BeneficenceBeneficence

AutonomyAutonomy

JusticeJustice Non-MaleficenceNon-Maleficence

VeracityVeracity

FidelityFidelityالمنفعة

اإلستقاللية

العدالة اإليذاء و الضرر عدم

اإلخالص

الصحة و الصدق

Genetic Counseling in Achondroplasia

• It is inherited in an AD manner.

• Homozygous achondroplasia is a lethal condition.

• > 80% of achondroplasia cases have parents with normal stature i.e.: de novo (new) gene mutation.

• Such parents have a low risk of having another child with achondroplasia.

• Prenatal molecular genetic testing is available.

Reem Sallam, MD, PhD

Genetic counseling - case

• An individual with achondroplasia who has a reproductive partner with normal stature has a 50% risk in each pregnancy of having a child with achondroplasia.

Achondroplasia (Heterozygous)Normal stature (Homozygous)

Child w/ achondroplasia. Child w/ normal stature

Reem Sallam, MD, PhD

Genetic counseling - caseWhen both parents have achondroplasia,

the risk to their offspring of having normal stature is 25%; of having achondroplasia, 50%; and of having homozygous achondroplasia (a lethal condition), 25%.

Achondroplasia (Heterozygous)Normal stature (Homozygous)

Child w/ achondroplasia.

Child w/ normal statureHomozygous achondroplasia

Reem Sallam, MD, PhD

Arabic/Islamic Communities

Unique featuresStrong Religious believes

Combined family Living style

Strong link to traditions and

customs

High rate of Consanguineous

marriages

Possibility of polygamy

Large family size

ReligiousAnd cultural

cohesionSpecial views on

Reproductive issues

Familyplanning

Abortion(IVF) In-vitrofertilization

AdoptionArtificial

inseminationFetalrights

Premarital Screening*Man -History

-(Physical Examination) BloodSample

Genetic Screening (Laboratory)

Carrier affected Normal

No Problem from marriage from

any Women

Safe Marriage

**Women –History -(Physical examination)

BloodSample

Genetic Screening (Laboratory)

Carrier affected NormalNo Problem from

marriage from any man

Safe Marriage

Genetic Counseling(advise no marriage with carrier or affected)

Not safe Marriage

Good Luck

Reem Sallam, MD, PhD