Genetic counselling can come up in the context of obstetrics, paediatrics and adult medicine. For example, during antenatal screening, paediatric community clinic or any adult specialty.
The objective of genetic counselling is to not only 'break bad news' about the condition to the patient or parent but to answer any questions they have about it. "Will they lead a normal life?" is a high priority question in the back of their minds. Since the context is genetics, another question will be "Will I pass this on to my children and grandchildren?"
This leads to why the following are hot topics in genetic counselling;
1. Regarding the patient
2. Regarding the consultation
3. Construct the family tree
4. The genetic condition
5. Patient options
If this is a first consultation, establish whether the patient would like genetic testing or not - not everyone wants to know!
Once the diagnosis has been made, in most genetic consultations, families are more than satisfied with the relief that comes with a diagnosis (at last!). In some consults, it does not end there.
6. Family members
If the patient has been diagnosed with a condition or confirmed a carrier, it may be of benefit for other family members to step forward for genetic testing as well. Do not assume that the patient will always want other family members to know. Genetic testing is a very sensitive subject.
Some patients are happy for the clinician to contact family members or tell them themselves to have testing done. Others may be more reluctant for various cultural or social reasons (i.e. arranged marriage prospects, disclosure of information to insurance companies or employers).
Further detail on drawing pedigrees can be found in the paediatrics skills section on Fastbleep.
(Down's (trisomy 21), Turner's (45, X0), Klinefelter's (XXY))
What kind of chromosomal abnormality is it? The wrong number of one type of chromosome (i.e. trisomies), the wrong number of an entire set of chromosomes (i.e. triploidy), the wrong shape (i.e. ring), the wrong sequence (i.e. inversion) or... A portion of the chromosome has been deleted or duplicated.
Once that has been established, the next question is how it happened in the first place. Is it due to a translocation? A non-disjunction during cell division? Germline mosaicism?
Penetrance --- the likelihood someone with the gene mutation will or will not express it in their phenotype. It could be age-dependent, complete or incomplete. In age-dependent penetrance, you are more likely to show signs and symptoms as you age (e.g. Huntington's Disease). In incomplete penetrance, not all people with the genotype will suffer with the phenotype (e.g. Brugada Syndrome).
Mosaicism --- Can be somatic or germline. If somatic - this is a new mutation during early embryogenesis so the phenotype is expressed only partially (e.g. cutaneous features of Neurofibromatosis type I in one dermatome only). If germline - a mutation present only in gonadal cells therefore the parent is unaffected but the offspring are.
Anticipation --- When the disease becomes increasingly severe with every generation. (ie Huntington's Disease)
(e.g. Cystic Fibrosis, Sickle Cell Disease)
Consanguinity --- When there are couplings between members within the same family autosomal recessive conditions become far more common.
Carrier Status --- When there is a known affected family member, the remaining question for unaffected relatives is whether they are carriers and could pass it on to their offspring.
There are 2 types - X-linked dominant inheritance (e.g. Rett syndrome) and X-linked semi-dominant inheritance (e.g. X-linked Hereditary Motor and Sensory Neuropathy)
The male foetus seldom survives pregnancy in an X-linked dominant inheritance whereas in an X-linked semi-dominant inheritance, they may survive but the disorder is very severe. Therefore the question of how severely affected the patient will be is inevitable.
(e.g. Duchenne Muscular Dystrophy)
A typical family tree will show a history of unaffected carrier mothers giving way to affected sons and either unaffected or carrier daughters... and if the affected son lives to a reproductive age, he would have unaffected sons and carrier daughters.
However it is not as simple as it sounds for the carrier daughter. Whether she manifests features of the phenotype depends on whether she has unfavourable skewing of X-inactivation. The girl inherits 2 X chromosomes where one of them can become inactivated. If the X chromosome carrying the mutation is inactivated, the girl remains unaffected. However if the other X chromosome is inactivated, she will become affected.
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