Genetics Flashcards
What is the genotype ?
Refers to the genes that we have. For example - having the gene that codes for brown eyes.
What is the phenotype ?
Refers to the physical expression of the genes that we have. For example - actually having brown eyes
What is a chromosome disorder ?
A condition where there is either a structural abnormality, an extra abnormal position or an abnormal number of chromosomes compared to normal.
What are deletion disorders ?
Occur where a portion of a chromosome is missing.
What are duplication disorders ?
They occur where a portion of a chromosome is duplicated.
The chromosome contains twice the number of copies of that gene.
What is a translocation disorder ?
Occurs when a portion of one chromosome is directly swapped with a portion of another chromosome. The swap can be balanced ( reciprocal ) or not balanced ( nonreciprocal ).
What is robertsonian translocations ?
Occurs in acrocentric chromosomes.
These chromosomes are 13, 14, 15, 21 and 22.
They loose the short arm completely and the 2 long arms connect to each other at the centromere essentially loosing a chromosome when they rid of the 2 short arms.
What is trisomy ?
Where the person has an extra chromosome. They have 3 copies of a particular chromosome.
What is patau syndrome ?
This is trisomy 13.
Patients have dysmorphic features, structural abnormalities and learning disability.
What is a characteristic feature of patau syndrome ?
Rocker bottom feet where the soles of the feet are convex ( rounded outwards ) in shape
What is Edwards syndrome ?
This is trisomy 18.
Dysmorphic features and learning difficulties
Rocker bottom feet
Which parent does a patient with a mitochondrial disorder inherit it from ?
Mother
What is diagnostic testing - genetics ?
Diagnostic testing involves testing a foetus or a person for a suspected genetic condition.
This is tested for via amniocentesis.
What is predictive testing ?
Involves testing a person for a specific gene mutation that has implications for them in the future. Examples - BRCA1 breast cancer gene
What is carrier testing ?
Involves testing parents or potential parents for the gene for a specific autosomal recessive condition in order to calculate the risk of passing it to their children.
What is karyotyping ?
Involves looking at the number of chromosomes, their size and basic structure.
This is helpful in diagnosing conditions like Down’s syndrome and Turner syndrome
What is microarray testing ?
Involves cutting up the genetic material from an individual using enzymes.
What is Down’s syndrome ?
Caused by 3 copies of chromosome 21.
How does Down’s syndrome present ?
Hypotonia ( reduced muscle tone )
Brachycephaly ( small head with a flat back )
Short neck
Short stature
Flattened face and nose
Prominent epicanthic folds
Upward sloping palpebral fissures
Single palmar crease
What is epicanthic folds ?
Folds of skin covering the medial portion of the eye and eyelid.
What are some complications of Down’s syndrome ?
Learning difficulty
Recurrent otitis media
Deafness - glue ear and conductive hearing loss
Visual problems - myopia, strabismus and cataracts
Hypothyroidism
Cardiac defects - ASD, VSD, patent ductus arteriosus and tetralogy of fallot
Leukaemia
Dementia
What are some antenatal screening for Down’s syndrome ?
Combined test - USS + maternal blood test
Triple test - involves beta-hcg, AFP and serum oestriol
What testing is done antenatally when suspecting Down’s syndrome ?
Chorionic villus sampling
Amniocentesis
What are some regular follow ups for someone with Down’s syndrome ?
Regular thyroid check ( 2 yearly )
Echocardiogram
Regular Audiometry
Regular eye checks
What is Klinefelter syndrome ?
Occurs when a male has an additional X chromosome making them 47 XXY.
When does Klinefelter’s syndrome usually present ?
Appear as male until puberty. After symptoms appear
How does Klinefelter’s syndrome present ?
Taller height
Wider hips
Gynaecomastia
Weaker muscles
Small testicles
Reduced libido
Shyness
Infertility
Subtle learning difficulties
What are some management options for Klinefelter’s syndrome ?
Testosterone injections
Advanced IVF techniques to allow fertility
Breast reduction surgery
What does Klinefelter’s syndrome increase the risk of ?
Breast cancer compared with other males
Osteoporosis
Diabetes
Anxiety and depression
What is turner syndrome ?
Occurs when a female has a single X chromosome making them 45 XO.
What are some features of turner syndrome ?
Short stature
Webbed neck
High arching palate
Downward sloping eyes with ptosis
Broad chest
Cubitus valgus
Underdeveloped ovaries
Late or incomplete puberty
Most women are infertile
What is cubitus valgus ?
Refers to an abnormal feature of the elbow. When the arm is extended downwards with the palms facing forward the angle of the forearm at the elbow is exaggerated, angle away from the body.
What are some associated conditions to turner syndrome ?
Recurrent otitis media
Recurrent UTI
Coarctation of the aorta
Hypothyroidism
Hypertension
Obesity
DM
Osteoporosis
What is the management of Turner syndrome ?
Growth hormone therapy
Oestrogen and progesterone replacement
Fertility treatment
What is noonan syndrome ?
A genetic condition
Inheritance - autosomal dominant
What are some features of noonan syndrome ?
Short stature
Broad forehead
Downward sloping eyes with ptosis
Hypertelorism - wide space between the eyes )
Prominent nasolabial folds
Low set ears
Webbed neck
Widely spaced nipples
What are some associated conditions for noonan syndrome ?
Congenital heart disease - pulmonary stenosis, ASD
Cryptochidism ( undescended testes ) can lead to infertility
Learning disability
Bleeding disorder
Lymphoedema
Increased risk of leukaemia and neuroblastoma
What is fragile X syndrome ?
Caused by a mutation in the FMR1 gene on the X chromosome. The FMR1 gene codes for the fragile X mental retardation protein, which plays a role in cognitive development in the brain.
X linked
What are some features of fragile X syndrome ?
Intellectual disability
Long, narrow face
Large ears
Large testicles after puberty
Hyper mobile joints
ADHD
Autism
Seizures
What is the management of fragile X syndrome ?
There is no cure.
Supportive and symptom control
What is the structural difference between adult and foetal haemoglobin ?
Foetal - 2 alpha and 2 gamma subunits
Adults - 2 alpha and 2 beta subunits
