Module 2

Fields within medical genetics

Fields within medical genetics

gytogenetics

molecular genetics

biochemical genetics

clinical aspects within medical genetics

general genetics (adults, peds, hereditary conditions)

metabolic genetics

cancer genetics (hereditary forms of cancer)

prenatal genetics (ultrasounds, screening)

what do clinical geneticists do

diagnosis (understanding)

genetic counselling & care of pts w genetic disorders

prenatal diagnosis

cancer genetics

newborn screening

metabolic genetics

population screening & preventative medicing

work w genetic counsellors (MSc training)

genotype

genetic makeup of person

phenotype

physical manifestation of inherited trait/disease

when to consider possible genetic disorder

development delay, congenital malformations, etc

positive family history of genetic disorder

recurrent miscarriages/stillbirths

consanguinity (autosomal recessive conditions)

ethnic background

George Mendel

father of genetics

scientist and friar

worked w 7 characteristics of pea plants

punnet squares

autosomal dominant

effects every generation

males & females affected equally

50% chance passing on gene

autosomal recessive inheritance

males and females equally affected

commonly in sibship

carrier is healthy

2 carriers may pass down mutation to children (25% chance restarts w pregnancy)

may skip generations

X linked inheritance

males almost exclusively affected (women are heterozygous)

gene transmitted from female to son

males cannot transmit (bc they pass down Y)

females may b mildly affected or fully affected due to skewed X inactivation

25% affected child (but depends on sex)

Mitochondrial DNA disorders

inherited from mother through egg

mitochondria have own circular DNA

severity varies based on mitochondria

maternal inheritance

maternal inheritance

all children will be affected

Autosomes

chromosomes 1-22

sex chromosome

23rd pair (XY male XX female)

chromosomal disorder

not mendelian but structural or numberal changes (cell division etc.)

numerical chromosome anomaly

error of meiosis (I or II)

results in aneuploidy (monosomy or trisomy) or triploidy

structural anomaly

error of recombination

down syndrome

extra chromosome 21

distinct facial features

developmental delays

heart defects

trisomy 21

93% nondisjunction (3 separate chromome 21)

5% translocation (extra 21 attached to 14)

^cant distinguish between 2 clinically)

reciprocal translocation

pieces of chromosome exchanged within pair

deletion

chunks of chromosome missing

duplication

chromosome extra piece

inversion

middle of chromosome is upside down

ring chromosome

ends are missing and come together to create ring

balanced reciprocal translocation

no clinical effects for carrier but risks of stillbirths/miscarriages

chromosomes intact and number is correct

outcomes in gametes differ and embryo can b effected

Trisomy 13 - Patau syndrome

Midline defects common

Clift palate

Extra fingers

80-90% die in first year

Severe developmental delay

trisomy 18 - edward syndrom

Most are female (5:1)

Frequent cardiac defects

80-90% die in first year of life

Marked developmental delay

Turner Syndrome (45X)

Puffy hands and feet at birth

Webbed neck

Coarctation of aorta

Short stature

Primary amenorrhea and infertility (streak ovaries)

Normal intelligence

Klinefelter syndrome 47, XXY

Tall stature

Excess breast developmemt (gynecomastia)

Small testes

May have learning disability

Infertility

Normal appearance