So what exactly is cystic fibrosis? So just like PKU and stickle cell anemia, cystic fibrosis is an autosomal recessive disease. So an individual will have the disease and will show it if they are homozygous recessive. So people with this condition basically lack that proper gene that is needed to synthesize an important chloride ion channel because they have two of these recessive alleles on some autosomal homologous pair. Now, as a result, there is an excessive build up of this very sticky, very thick and very viscous mucus that is found in the passageway of the lungs as well as in our liver, in our pancreas and in our small intestine. So as a result of this thick mucus layer, our body cannot actually rid itself of this mucus layer properly.