16. Genetic Counselling Flashcards
why are families referred for genetic counselling: child
- birth anomalies
- dysmorphic features
- learning difficulties
why are families referred for genetic counselling: adult
- diagnosis
- predictive testing
- carrier testing
- family history
- foetal loss or recurrent misscarriages (x3)
why are families referred for genetic counselling; pregnancy
- known genetic disorder
- abnormality detected on screening
genetic counselling
the process of helping people understand and adapt to the medical, psychological and familial implications of genetic contributions to disease
what proportion of patients have a genetic disease and congenital malformations
4-5%
what proportion of patients have chronic disease with major genetic component
10% of adults
what are the two basic types of Genetic analysis
cytogenetic analysis
molecular analysis
what is cytogenetic investigation
looking at the number and structure of chromosomes
what are numerical chromosomal abnormalities
conditions that are caused by the loss or gain of a whole chromosome
explain the three different patterns of chromosomes that can cause down syndrome
- 95% of people have three separate copies of chromosome 21
- 4% have the extra copy of chromosome 21 because of a Robertsonian translocation
- 1% have mosaicism with normal and trisomy 21 cell lines (usually milder features because of the presence of normal cells)
Non-Invasive Prenatal Diagnosis (NIPD)
NIPD is a prenatal screening test that can be performed beginning around the 10th week of pregnancy
small fragments of cell-free DNA from the placenta enter the mothers bloodstream
a sample of this is analyzed for evidence of extra or missing fetal DNA segments
reciprocal translocation (chromosomal disorders)
conditions that are caused by a loss of gain of a piece of a chromosome, or by chromosomal material arranged differently
explain a balanced translocation
two chromosomes break when cells are dividing during egg or sperm formation or early development of a baby.
two fragments “swap places”
unbalanced translocation
when there is an extra piece of one chromosome
and/ or a missing piece of another
explain how microarray is carried out
- you have the patient sample to be analyzed and also a reference sample
- fluorescent labels are added to each sample, to help differenciate them
- samples are then mixed
- sample is then added to a microarray slide so that it can hybridize
- microarray slide is scanned and the fluorescent signal at each spot on the microarray corresponds to the abundance of the target sequence in the sample
what is the benefit of microarray
picks up small gains or losses which would be missed by conventional karyotyping
what is the genetic clinicans agenda in a genetic counselling meeting
- ascertaining the family’s understanding about the reason for referral and expectations about what will be gained through the genetics consultation
- assessment of the family’s beliefs about causation and of emotional and cultural issues that may affect their perception of the information given
- obtain family history
what might be the patients agenda at a genetic counselling session ?
is my condition inherited?
will my children get it ?
what can we do about it ?
can i have genetic testing ?
what happens at a genetic counselling session
- establish the diagnosis
- explain inheritance pattern and risk
- explain availability of testing
- give patients time to discuss how they feel
steps on who to include when making a pedigree/family tree
- you husband and your kids
- you siblings
- your siblings family
- your parents
- you mothers siblings
- your mothers sibling’s families
- your mothers parents
- relatives of your father
- your husbands parents
what are the three types of single gene disorder inheritance
- autosomal dominant
- autosomal recessive
- X-linked
features of autosomal dominant conditions
- males and females are affected
- multiple generations are affected
- male and female transmission
- condition may be variable in its presentation
- condition may be present later in life
common autosomal dominant conditions
- bowel cancer
- AD polycystic kidney disease
- neurofibromatosis
- huntington’s disease
- myotonic dystrophy
explain autosomal recessive inheritance
- males and females equally affected
- both parents must be carriers for a single copy of the responsible gene in order for the child to be affected
- recurrence risk is 1 in 4 for each offspring of parents
common autosomal recessive conditions
- haemochromatosis
- cystic fibrosis
- Freidreich’s ataxia
- spinal muscular atrophy
features of X-linked Recessive inheritance
- incidence of the condition is much higher in males than females
- all daughters of affected males will be carriers
- the condition is never transmitted from father to son
x linked recessive inheritance - hemizygote
one copy of an altered gene on the X chromosome causes the disease in a male
X-linked recessive inheritance : heterozygote
an altered copy of one of the X chromosome pair causes carrier status in a female
common X linked recessive conditions
- Duchenne Muscular dystrophy
- haemophilia
- fragile x
‘skipped generations’ - dominant conditions
- gene change may not be fully penetrant
- condition may be so mild as to appear to skip a generation
when should i refer a patient to clinical genetics? / what are features suggestive of a genetic condition?
- if there are multiple closely related people with the same condition
- disorders with earlier age of onset than typical (premenopausal breast cancer, colon cancer, heart disease)
- sudden cardiac deaths in people who seemed healthy
- three or more pregnancy losses
