Hereditary genetic disorders Flashcards
Give an example of a genetic disorder
- originating from genetic differences in DNA
- passed from parent to child
Fragile X syndrome
caused by mutation in the X chromosome - more common in males because they only have one X chromosome. Females have two so if they have the mutation, they have a ‘back up’ gene. Females can be carriers, but the symptoms are twice as common in males.
What are the symptoms of Fragile X Syndrome?
At the age of 2, the have delayed speech and language development. Most males and 1/3 of females will have some types of intelectualldisability, or lowered IQ. Some have ADHD, are impulsive and aggressive behaviour. Some can have autism or epilsepsy
How do the brains of Fragile X sufferers differ from normal brains?
They have less grey and white matter in their front and temporal lobe (compared to those with similar autistic traits)
What are non-inherited genetic disorders?
They are spontaneous genetic differences that have arisen for the first time ever in the family. This happens during meiosis in the gametes (normally the egg). They are not present in the parents’ genetic material. Errors are present every time an egg is fertilised.
Describe Down’s syndrome causes and symptoms
It is caused by 3 copies of the chromosome 21.
It causes mild to moderate intellectual disability and delayed language skills. Behavioural problems can occur such as low attention and impulsive. They have a distinctive facial appearance and a higher risk for some medical problems (heart defects, digestive problems and early cognitive decline)
How do brains of those with Down’s differ to normal brains?
They have a lower total brain volume, especially in their frontal and temporal lobe, and hippocampus.
This could increase risk of dementia.
Describe William’s syndrome causes and symptoms
This occurs due to a section of chromosome 7 being missing. Due to this a number of genes are not available.
As a result, the sufferer will have problems with visial-spatial processing - they are able to adequately describe the characteristics of an object but will not be able to draw it. They are very chatty and sociable but have phobias of sudden loud noises, like balloons.
However, they are socially immature and have ‘elfin’ face.
They may have heart problems and problems with connective tissue
How do brains of those with Williams differ to normal brains?
Their cortical layers are thicker and thinner in different places. There are also gyral and sulcal anomolies, and differences in their white matter connectivity - increased fibres tract thickness in superior and inferior longitudinal fascicullus - there are very subtle differences
Give an example of an environmentally caused disorder
The foetal alcohol syndrome spectrum (FASS) is caused by the mother’s alcohol intake during her pregnancy and affects 1 in 1000 live births - so it is quite common.
There are many IDs (how much alcohol, how far into pregnancy, how often consumed, mother and foetus’ sensitivity to alcohol)
What are the symptoms of FASS?
They have distinctive facial features (thin upper lip, small head short nose) and lower height and weight compared to normal children. `
How do the brains of those with FASS differ to normal brains?
They have lower overall brain volume and can lead to brain damage and even death. The reduced corpus collosum can lead to hyperactivity and reduced cerrebellum can lead to poor motor skills. Abnormal dendrites in the hippocampus can cause leading difficulties.
Give an example of disorders with environmental and genetic risk
Autism can be caused by many different genes (different symptoms) - that can cause complex symptoms by interacting. For example, the GABA neurotransmitter and oxytocin hormone.
It can also be caused by ‘de novo’ mutations - new variations or unknown genetic disorders.
There is mixed evidence for gestational diabetes and birth order. Higher paternal age, exposure to toxins and maternal infection, and autoimmune diseases
there is NO single cause
Describe the symptoms of autism
They have difficulties in social communications, and take part in repetitive behavioural patterns, interests and activities. They have fine and gross motor difficulties, sleep disorders and epilepsy (30% have seizures)
These symptoms must be present in the early developmental period - and cause significant impairment.
They should not be explained by intellectual disability
How do the brains of those with autism differ to normal brains?
They have an increased total brain volume and reduced corpus collosum, and bigger amygdala, increased grey matter volume in frontal and temporal areas
What are the causes of dyslexia?
It can be caused by a number of genes - that can be working independently or interact. For example ROBO 1 in chromosome 3.
Environmental causes include the home literacy environment (books at home, reading with parents), their socio-economic status (family stress), premature birth and it seems males are more prone to this.
The causes seem to be equally genetic and environmental - but other factors can offer protection
