GENETIC COUNSELLING

Compiled by Dr Karen Milstein 1st

Quarter 2016

Genetic counselling involves the sharing of knowledge of genetic diseases with people who are at an increased risk of being affected with a genetic disorder or of passing it on to their offspring. Information is provided on the inheritance patterns of genetic conditions and their recurrence risks. Genetic counselling assists people in making informed personal and medical decisions. The concerns of patients, their families and healthcare providers are addressed. Support in dealing with these conditions is given to the patients and their families. The professionals involved in genetic counselling are genetic counsellors and clinical geneticists, who often work together.

Genetic counsellors are trained professionals who help people and their families understand and cope with genetic

conditions.

Clinical Geneticists are medical doctors with special training in Genetics. They perform clinical examinations and order

laboratory tests to diagnose the causes of birth defects and other genetic conditions. They advise treatment and

management options. REASONS FOR SEEKING GENETIC COUNSELLING

There are many reasons for seeking genetic counselling, including: · A family history of a genetic condition (e.g. cystic fibrosis, muscular dystrophy) · Genetic screening for diseases more common in a high risk population (e.g. Ashkenazi Jewish screening) · A family history of breast and/or ovarian cancer (BRCA) or other cancers (e.g. colon) · To discuss abnormal results from tests performed during pregnancy (e.g. maternal blood, non-invasive prenatal test

(NIPT), chorionic villus sampling (CVS) and amniocentesis) · Advanced maternal age (> 35 years) and the risk of chromosomal abnormalities · A woman with recurrent miscarriages or neonatal/infant deaths · Infertility · Effects of teratogens in a pregnancy (e.g. alcohol, chemicals, illicit drugs, X-rays) · A genetic condition or birth defect in a previous pregnancy · A child with birth defects, disabilities or a condition detected on newborn screening · To exclude a genetic cause for developmental delay, dysmorphic features or a health problem MODES OF INHERITANCE OF GENETIC CONDITIONS

AUTOSOMAL RECESSIVE INHERITANCE (e.g. cystic fibrosis, Tay-Sachs disease, albinism) · Both parents carry one faulty gene for the condition and are referred to as CARRIERS · Carriers are well and do not manifest symptoms of the condition · When two carriers have children, with each pregnancy, there is a 25% chance of having an AFFECTED child, a 50%

chance of having a child who is a CARRIER and a 25% chance of having an UNAFFECTED child · Autosomal recessive disorders are not always seen in every generation of an affected family

https://edsociety.co.uk/what-is-ed/genetics/inheritance-patterns/

AUTOSOMAL DOMINANT INHERITANCE (e.g. Huntingtons disease, myotonic dystrophy) · An affected person only has to have one faulty gene for the condition · Each child of an affected parent has a 50% chance of being AFFECTED with the condition and a 50% chance of being

UNAFFECTED with the condition · Autosomal dominant disorders are often seen in multiple generations within the family

https://edsociety.co.uk/what-is-ed/genetics/inheritance-patterns/

X-LINKED RECESSIVE INHERITANCE (e.g. haemophilia, Duchenne muscular dystrophy) · Females carry a gene fault on one of their X chromosomes and are CARRIERS

* Each female child of a female carrier has a 50% chance of being a CARRIER and a 50% chance of NOT being a carrier * Each male child of a female carrier has a 50% chance of being AFFECTED and a 50% chance of being UNAFFECTED

· All males with a gene fault on their X chromosome will be AFFECTED

* ALL of the female children of an affected male will be a CARRIER, but are not expected to have symptoms of the condition

* NONE of the male children of an affected male will be affected nor a carrier

https://edsociety.co.uk/what-is-ed/genetics/inheritance-patterns/

X-LINKED DOMINANT INHERITANCE (e.g. fragile X syndrome) · All people will be AFFECTED as the gene fault only needs to be present on one X chromosome to have the condition · Generally males experience more severe symptoms than females · All daughters of an affected male will have the condition, but none of the sons will have the condition · Each child of an affected female has a 50% chance of being AFFECTED with the condition and a 50% chance of being

UNAFFECTED with the condition.

https://edsociety.co.uk/what-is-ed/genetics/inheritance-patterns/

MITOCHONDRIAL INHERITANCE (e.g. Leber hereditary optic neuropathy) · Only females pass mitochondrial gene faults to their male and female children, as only maternal ova contribute mitochondria to the

developing embryo

https://thenaturalhistorian.com/2016/04/07/testing-yec-hyper-evolution-from-common-ancestors-comparisons-of-mtdna-genome-diversity-in-mammals/

MULTIFACTORIAL INHERITANCE (e.g. diabetes, certain cancers, schizophrenia) · Multiple genes in combination with lifestyle and environmental factors are involved · There is no clear-cut pattern of inheritance, thus making it difficult to determine a persons risk of being affected or passing

on the disorder

Genetic counselling is available through Lancet Laboratories. To discuss a genetic test or to arrange counselling, please

contact:

Dr Karen Milstein, Clinical Geneticist Tel: 086 152 6238 E-mail: karen.milstein@lancet.co.za

References

1. http://www.who.int/genomics/professionals/counselling/en/ 2. https://www.nlm.nih.gov/medlineplus/geneticcounseling.html 3. http://www.geneticcounselling.co.za/genetic-counselling.php 4. https://ghr.nlm.nih.gov/handbook/inheritance/inheritancepatterns 5. https://www.geneticsupportfoundation.org/genetics-and-you/pregnancy-and-genetics/prenatal-genetics-101

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