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Recessive disease occurs when two mutated copies of a gene are inherited, one from each parent.听
In recessive听bestrophinopathy,听a patient inherits听two mutated copies of the听BEST1听gene, one from each parent.听The only听bestrophinopathy听known听to follow a recessive mode of inheritance is autosomal recessive听bestrophinopathy听(ARB). In ARB, the presence of two mutated/defective copies of the听BEST1听听gene听can lead to听the听production of proteins that no longer function correctly听or are completely absent, leading to disease.听
We听inherit one copy of听the听BEST1听gene from our mother and one from our father. In听recessive disease,听both听inherited听copies听of听BEST1听contain a disease-causing mutation. In order to inherit two faulty copies of the gene,听each parent must have a faulty copy of the gene. Parents who have a mutated听BEST1听gene, but do not show any symptoms of disease are known as carriers. Two carrier听parents, with no diagnosed听bestrophinopathy,听can have a child with听ARB听if the child inherits both mutated copies.听听
If both parents have a single听defective听copy of the听BEST1听gene the听chances of having a child with recessive disease is 25%听in each pregnancy, and there is a 50% chance of having a child who is a carrier.听听The image below shows this schematically:听
