15. Clinical Genetics

Question 1

what are the different parts of clinical genetics

Answer 1

1. diagnosis
2. advice
3. support
4. register of genetic disorders
5. research

Question 2

what are the indications for genetic consultation. why do people come to the clinic

Answer 2

1. known or suspected genetic disease in the family
2. birth defects
3. unexplained intellectual disability
4. advanced maternal age
5. family history of potentially hereditary cancers
6. recurrent pregnancy loss
7. teratogen exposure
8. consanguinity

Question 3

what happens during a clinical genetics consultation

Answer 3

• document diagnosis
• document pedigree (family tree)
• determine mode of inheritance
• explain diagnosis and inheritance
• explain options open to family members

Question 4

what is the methodology for taking a family history

Answer 4

• 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

Question 5

what are the aims when taking a family history

Answer 5

• demonstrate mode of inheritance of disorder in family
• identification of other family members at risk

Question 6

what is the most common mechanism for chromosome disorder

Answer 6

meiotic nondisjunction

Question 7

if a first or second degree relative of the parent has Down’s syndrome, what are the chances of their child having Down syndrome

Answer 7

very small risk

Question 8

what does non-dysjunctional mean

Answer 8

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,

Question 9

if a couple has had a previous child with down syndrome, what is the recurrence risk

Answer 9

mother under 35: recurrence risk of 1%

mother over 35: recurrence risk slightly higher

Question 10

Presymptomatic diagnosis of autosomal dominant disorders

Answer 10

1. clinical examination
2. biochemical testing
3. molecular genetic testing

Question 11

huntingtons disease

Answer 11

progressive neurological disorder - onset in middle age. incurable, death in about 10 years from onset

Question 12

what is the genetic testing that is now available for Huntingtons disease able to tell us

Answer 12

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

Question 13

what is the new genetic test unable to tell us about HD

Answer 13

cannot predict when, how or in what way a person will develop HD

Question 14

carrier testing in autosomal recessive disorders

Answer 14

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

Question 15

excess risk of autosomal recessive disorders due to consanguinity

Answer 15

isolated first cousins: 3% excess risk

isolated second cousins: 1% excess risk

double first cousins: 10% excess risk

Question 16

what is incest

Answer 16

a relationship between first degree relatives

Question 17

what is the risk to offspring of incestuous relationships

Answer 17

25% chance of child with intellectual disability
10-15% of child with autosomal recessive disorder
10% chance of child with a significant congenital malformation

Question 18

what are the choices for parents of a child with an autosomal recessive disorder

Answer 18

• have no further children
• take 1/4 chance of affected child
• consider prenatal diagnosis
• consider donor insemination
• consider adoption
• consider preimplantation genetic diagnosis

Question 19

what is Prenatal diagnosis by amniocentesis

Answer 19

a medical procedure used during pregnancy to diagnose certain disorders and chromosomal abnormalities in the fetus

Question 20

what happens during amniocentesis

Answer 20

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.

Question 21

what are the risks associated with amniocentesis

Answer 21

small risk of complications, including miscarriage, infection or injury to the fetus

Question 22

what is transabdominal chorionic villus sampling CVS

Answer 22

a prenatal diagnostic procedure used to detect genetic disorders and chromosomal abnormalities in the fetus during early pregnancy

Question 23

how does CVS work

Answer 23

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

Question 24

pros and cons of CVS

Answer 24

it gives us an earlier result but it also has the chance of causing miscarriage

Question 25

explain preimplantation genetic diagnosis technique

Answer 25

it is the genetic testing of an embryo generated by IVF prior to implantation
embryos with genetic alteration are not implanted

Question 26

who uses preimplantation genetic diagnosis

Answer 26

initially intended for those at significant risk of having a child with a serious handicap

Question 27

non invasive prenatal genetic disorders for single gene disorders

Answer 27

carrier out on maternal blood at 9 weeks gestation
- for couples with high prior risk single gene disorder