Flashcards in Nitrogen 3 Deck (19):
What usually causes an inherited metabolic disorder?
A defect in a single gene
What effect does an IMD cause?
Enzyme abscence of defieciency resulting in abnormal synthesis of amino acids, proteins, carbohydrates & lipids.
When do most IMDs present?
In infancy or childhood
What 3 effects do enzyme defects have on the reaction pathway?
- A build up of precursor molecules
- A decreased formation of product
- An increased production of unwanted products (which may be toxic)
Where do a childs genes come from?
A child recieves one allele of each gene from each parent, giving them two alleles for every gene.
Define autosomal dominant inheritance:
The child requires just one defective allele to have the condition even if the other parent gave them a healthy allele
Define Autosomal Recessive Inheritance:
The child requires two defective alleles in order to present with the condition. this means some people will carry the defective gene without having the condition (carriers).
Which type of autosomal inheritence do most inborn errors of metabolism (IEMs) have?
Most IEMs have automsal recessive inheritance, i.e. heterozygous children are phenotypically normal.
How many IMDs are there in the urea cycle?
6, one for each important enzyme
Whats the most common IMD in the urea cycle?
Ornithine transcarbamoylase (OTC) deficiency
What kind of inheritance is occurs in urea cycle IMDs?
5 display autosomal recessive inheritance.
OTC is x-linked
What is X-linked inheritance?
Some genes are specific to the X or Y chromosome
X-linked inheritance refers to genes present only on the X chromosome.
This means boys will show the phenotype for whatever X chromosme they receive as they only have one
Girls will show typical dominant/recessive patterns for X-linked genes as they have two X chromosomes.
What is the main result of Urea cycle disorders?
A buildup of toxic ammonia. (Hyperammonaemia) which can cause accelerated breathing by stimulating a specific part of the brain and long term brain damage.
When do Urea cycle disorders typically present?
Enzymes catalyse the conversion of amino acids to what 4 substances?
Hormones, Pigments, Amino Acids and neurotransmitters
What causes phenylketonuria (PKU)?
A deficiency in phenylalanine hydroxylase (PAH) deficieny).
How is PKU inherited?
By automsomal recessive inheritenace
What are the effects of PKU?
Insufficinet tyrosine for conversion to melanin and other products.
Build up of Phenylalanine and unwanted metabolites which build up in the nerves and cause abnormal brain development