autosomal recessive disease and reproduction Flashcards
Where are all recessive condition mutations located on a chromsome
Between 1-22 on chromosome = autosomes
What is compund heterozygous vs recessive
Compund heterozygous - both alleles contain a different variant affected by recessive condtioon
Recessive = 2 copies of same gene with same mutation on that chromosome
incidence of CF in the UK
1 in 2500
What causes cystic fibrosis
CFTR gene mutation on chromsome 7 , most commonly delta 508 mutation
Cystic fibrosis transmembrane conductance regulator = cell mebrane chloride transporter
What is tay sachs disease
HEXA gene mutation codes for enzyme that breaks down toxic CNS products - severe neurodegnerative condition
What chances do a carrier coupleof having diseased children (each has one faulty copy) recessive disease
1 in 4 unaffected entirely or affected child
1 in 2 carrier
Of the unaffected children 2 in 3 are carrers
What are the outcomes of pregnancy for affected and unaffected partner recessive disease
All offspring will be carriers
if other parent is carrier offspring - 1in 2 chance of affected childrne
Direct children otherwise not affected unless chromsome deletions etc
Features of autosomal recessive pedigrees
Horiozontal pattern - siblings affected
Cant always follow disease through pedigree (usually not one generation after the oterh)
Parents and children of afected individuals usually unaffected
Males and females affected equally
More likely in consaguineous pedigrees or closed populations
What is consanguinity
Having children with relations second cousin or closer
ASK FH
How is consagnuinity shown on pedigree
Double horizontal line between couple
How is carrier testing offered
If someone found to be a carrier, offer testing to first degree relatives and partners
Find out chance of having affected child
Specifically test for idetifited mutation
Not done in children
How calculate risk calculation of passing on autosomal recessive disease
3 things - father and mother must be a carrier, both must pass on mutation - 1 in4
Chance of mum being a carrier x chance of dad being a carrier x 0.25
eg population chance of being a carrier or known carrier status = 1
What aware about when testing recessive disorders in partners of carriers
90% of CFTR mutations tested for - reduces risk significantly but could have rarer mutation
Consider different ethnic groups who may have different genetic mutations
What is pre implantation genetic diagnosis
Assisted production eg IVF/ICSI embryo biopsy taken from day 5-7
Testsing by FISH analysis, SNP array or test for known mutation in single gene disorder
What need to meet for PGD crtieria
Like IVF
Age, health, already have child?, couples relationship eg living together
