More stories from Genetic clinic Flashcards
(30 cards)
What is gene imprinting?
Where certain genes are inactivated depending on parent of origin
How does genomic imprinting occur?
Methylation of certain DNA segments that marks them, causing them to be inactivated, leaving only one parental chromosome expressed
Which base is methylated?
5th C on Cytosine is methylated
In maternal imprinting, will offspring of males be affected?
Yes, as the faulty gene is not masked
What are two chromosome imprinting disorders and on which parental chromosome does this occur on?
Prader-Willi
PATERNAL
Angelman
MATERNAL
Chromosome 15
What are symptoms of Prader-Willi syndrome?
Obesity
Mental impairment
Behavioural problems
Muscle hypotonia
Short stature
Delayed, incomplete puberty
How is Prader-Willi managed?
Diet restriction
Exercise
Hormone treatment
What are symptoms of Angelman’s syndrome
Developmental delay
Microcephaly
Seizures
Happy demeanour
How is Angelman’s treated?
Depends on symptoms
- anti-convulsant
Other than that - normal life-span
What is uniparental isodisomy?
Where non-disjunction occurs in meiosis II, leading to the formation of a gamete with two chromosomes.
This is fertilised by a single chromosome, which is lost, leading to a zygote with two chromosomes, both from one parent.
Why do syndromes like Prader Willi and Angelmans occur?
As there is only one gene active, a deletion means complete loss of genetic material, due to the inability of material to be accessed from the other allele.
Hence, disorder occurs
HOw many genes does the mitochondrial genome contain?
37
By which parent does mitochondrial inheritance go through?
Maternal, as the ovum contains mitochondria
Why might the phenotype of mitochondrial diseases vary?
Heteroplasmy, not all mitochondria are diseased
Give some examples of mitochondrial disorder
MELAS - Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes
LHON - Leber’s hereditary optic neuropathy
MERRF
What is MELAS
Mitochondrial Encephalomyopathy with Lactic Acidosis and Stroke-like Episodes
1:13000
Neurodegenerative disorder
What are the symptoms and prognosis of MELAS?
Muscle weakness
Episodic seizures
Headache
Hemiparesis
Vomiting
Dementia
Progressive, ultimately fatal
What causes MELAS?
Point mutations in various genes
MTTL1 - Phenylalanine rather than Leucine is made
What is LHON
Optic neuropathy
1:50000
More common in males
What are the symptom sand prognosis of LHON
Bilateral loss of vision
Painless
Optic atrophy till blind
Why does LHON occur?
Mitochondria are dysfunctional, so optic nerve dies
Due tomutation in NADH dehydrogenase
How can mitochondrial diseases be prevented
3rd parent
- Combine oocyte (no genetic dataa) of 3rd parent w maternal nucelar genoem then fierslise
What are inborn errors of metabolism?
Where defective ezymes result in the ability of substrate metabolism for energy
What does the UK Newborn Screening Program screen for?
PKU
Congenital Hypothyroidism
Sickle-cell disorders
CF
MCADD - medium chain acyl-coA dehydrogenase deficiency
