15. Clinical Genetics Flashcards
what are the different parts of clinical genetics
- diagnosis
- advice
- support
- register of genetic disorders
- research
what are the indications for genetic consultation. why do people come to the clinic
- known or suspected genetic disease in the family
- birth defects
- unexplained intellectual disability
- advanced maternal age
- family history of potentially hereditary cancers
- recurrent pregnancy loss
- teratogen exposure
- consanguinity
what happens during a clinical genetics consultation
- document diagnosis
- document pedigree (family tree)
- determine mode of inheritance
- explain diagnosis and inheritance
- explain options open to family members
what is the methodology for taking a family history
- collect accurate info on as many members as possible
- if necessary get additional info from other family members
- use conventional symbols
- document full names, age at death and diagnosis
what are the aims when taking a family history
- demonstrate mode of inheritance of disorder in family
- identification of other family members at risk
what is the most common mechanism for chromosome disorder
meiotic nondisjunction
if a first or second degree relative of the parent has Down’s syndrome, what are the chances of their child having Down syndrome
very small risk
what does non-dysjunctional mean
the chromosomes fail to separate during cell division, leading to an incorrect distribution of chromosomes in daughter cells
This can result in gametes with too many or too few chromosomes,
if a couple has had a previous child with down syndrome, what is the recurrence risk
mother under 35: recurrence risk of 1%
mother over 35: recurrence risk slightly higher
Presymptomatic diagnosis of autosomal dominant disorders
- clinical examination
- biochemical testing
- molecular genetic testing
huntingtons disease
progressive neurological disorder - onset in middle age. incurable, death in about 10 years from onset
what is the genetic testing that is now available for Huntingtons disease able to tell us
a) you don’t have abnormal gene - self and children OK
b) do have abnormal gene - will develop HD, and children at 50% chance of having abnormal gene
what is the new genetic test unable to tell us about HD
cannot predict when, how or in what way a person will develop HD
carrier testing in autosomal recessive disorders
the parent of a person affected by an autosomal recessive disorder is an obligate carrier. carrier testing for other family members will depend on the specific disease and sometimes their ethnic background
excess risk of autosomal recessive disorders due to consanguinity
isolated first cousins: 3% excess risk
isolated second cousins: 1% excess risk
double first cousins: 10% excess risk
what is incest
a relationship between first degree relatives
what is the risk to offspring of incestuous relationships
25% chance of child with intellectual disability
10-15% of child with autosomal recessive disorder
10% chance of child with a significant congenital malformation
what are the choices for parents of a child with an autosomal recessive disorder
- have no further children
- take 1/4 chance of affected child
- consider prenatal diagnosis
- consider donor insemination
- consider adoption
- consider preimplantation genetic diagnosis
what is Prenatal diagnosis by amniocentesis
a medical procedure used during pregnancy to diagnose certain disorders and chromosomal abnormalities in the fetus
what happens during amniocentesis
a thin needle is inserted through the mother’s abdomen into the amniotic sac surrounding the fetus.
A small amount of amniotic fluid, which contains fetus cells is then withdrawn for analysis.
Cells are examined for genetic abnormalities.
what are the risks associated with amniocentesis
small risk of complications, including miscarriage, infection or injury to the fetus
what is transabdominal chorionic villus sampling CVS
a prenatal diagnostic procedure used to detect genetic disorders and chromosomal abnormalities in the fetus during early pregnancy
how does CVS work
Thin tube or needle is inserted either through the cervix or through the abdomen into the uterus, Taking cells from the tissue not from the placenta
pros and cons of CVS
it gives us an earlier result but it also has the chance of causing miscarriage
explain preimplantation genetic diagnosis technique
it is the genetic testing of an embryo generated by IVF prior to implantation
embryos with genetic alteration are not implanted
who uses preimplantation genetic diagnosis
initially intended for those at significant risk of having a child with a serious handicap
non invasive prenatal genetic disorders for single gene disorders
carrier out on maternal blood at 9 weeks gestation
- for couples with high prior risk single gene disorder
