GENETICS Flashcards
Myotonic muscle dystrophy
Myotonic dystrophy is characterized by progressive muscle wasting and weakness. People with this disorder often have prolonged muscle contractions (myotonia) and are not able to relax certain muscles after use.
Symptoms of myotonic muscle dystrophy
-muscle weakness,
- muscle spasm
which will affect their mobility.
-They will have an increased risk of getting
diabetes which might be difficult to
treat.
-They will have heart
problems. (abnormalities of the electrical signals that control the heartbeat (cardiac conduction defects))
-They will have cataracts.
-They will have an increased risk to
sometimes tumours
What causes duchenne muscular dystrophy
DMD is caused by an absence of dystrophin, a protein that helps keep muscle cells intact.
What is TRISOMY 21
downsydrome
Types of Translocations
Reciprocal
robertsonian
What is reciprocal translocation?
When a part of two chromosomes switches over
-As long as balanced = usually no harmful affects bc got the correct amount of info
What is robertsonian transloacation?
When one chromosome attached to another so looks like 45 present
A v common deletion syndrome
Chromosome 22q11 deletion syndrome
Other names of 22q11 syndrome
Digeorge syndrome
Velocardialfacial syndrome
Features of 22q11 Deletion Syndrome
Characteristic facial features (?) Congenital heart disease (≈74%) Palatal abnormalities (≈69%) Learning difficulties (≈70-90%) Psychiatric problems (?) Immunodeficiency (≈ 77%) Hypocalcaemia (≈50%) Renal abnormalities (≈37%) Approx. 90% de novo, 10% inherited
Mendel’s 3 laws of genetics
- Segregation
- Dominance
- Independant assortment
Allelic heterogeneity
where different mutations within the same gene result in the same clinical condition e.g. cystic fibrosis. Thus an individual with an autosomal recessive condition may be a compound heterozygote for two different mutations
Features of Autosomal Recessive Inheritance
Male and females affected in equal proportions
Affected individuals only in a single generation
Parents can be related, i.e. consanguineous
Most common Autosomal recessive condition
Cystic fibrosis
Diagnostic test for cystic fibrosis
Sweat testing (not genetic analysis)- looks for increased Chloride ions in sweat
Cystic fibrosis can be cvaused by over 1000 mutations this is called
Mutational heterogeneity
What is cystic fibrosis
inherited condition that causes sticky mucus to build up in the lungs and digestive system. This causes lung infections and problems with digesting food.
Symptoms of cystic fibrosis
recurring chest infections
wheezing, coughing, shortness of breath and damage to the airways (bronchiectasis)
difficulty putting on weight and growing
jaundice
diarrhoea, constipation, or large, smelly poo
a bowel obstruction in newborn babies (meconium ileus) – surgery may be needed
Why does cystic fibrosis cause so many problems
The build-up of sticky mucus in the lungs can cause breathing problems and increases the risk of lung infections. Over time, the lungs may stop working properly.
Mucus also clogs the pancreas (the organ that helps with digestion), which stops enzymes reaching food in the gut and helping with digestion.
This means most people with cystic fibrosis don’t absorb nutrients from food properly and need to eat more calories to avoid malnutrition.
Genotype - phenotype correlations in cystic fibrosis EXample
If have F508 mutation in both alleles then =
pancreatic insufficiency and chronic lung disease
If have F508 in one allele and R117H in other = majority are pancreatic sufficient but have chronic lung disease - Milder symptoms
Consanguinity meaning
Reproductive union between two relatives.
Autozygosity
Homozygosity by descent, i.e. inheritance of the same altered allele through two branches of the same family.
Typical features of autosomal dominant inheritance
Male and females affected in equal proportions
Affected individuals in multiple generations
Transmission by individuals of both sexes, to both sexes
But don’t forget penetrance & variability!
Pentrance meaning
The percentage of individuals with a specific genotype showing the expected phenotype
Expressivity
Refers to the range of phenotypes expressed by a specific genotype
Meaning of de novo mutation and example of disease caused by this
New mutation
- Example – Neurofibromatosis type 1, up to 50% of cases occur as result of de novo mutation
What is neurofibromatosis
genetic condition that causes tumours to grow along your nerves. The tumours are usually non-cancerous (benign) but may cause a range of symptoms.
Symptoms of neurofibromatosis
pale, coffee-coloured patches (café au lait spots)
soft, non-cancerous tumours on or under the skin (neurofibromas)
clusters of freckles in unusual places – such as the armpits, groin and under the breast
problems with the bones, eyes and nervous system
Anticipation meaning and example of disease
Whereby genetic disorder affects successive generations earlier or more severely, usually due to expansion of unstable triplet repeat sequences
Example Myotonic dystrophy
Somatic Mosaicism
Genetic fault present in only some tissues in body
Gonadal (germline) Mosaicism
Genetic fault present in gonadal tissue
Late-onset
Condition not manifest at birth (congenital), classically adult-onset
Example – Hypertrophic Cardiomyopathy
Sex-limited
Condition inherited in AD pattern that seems to affect one sex more than another
Example – BRCA1/2
