There is connection between two, you can say it to be long connection between the two. You are naturally resistant to malaria, when you are having sickle cell trait. That means when you have mutation in single chromosome. That makes you fit to survive in the malaria endemic zone. So this gene is naturally selected in the malaria endemic zone. So you find sickle cell anaemia in malaria endemic zone only. The normal people will be killed by malaria in such a region. The biggest problem faced by the military in world war one and two was malaria and not the opposite forces. (So it is better to fight with malaria and not with each other!) The heavy price you for such protection against malaria is given in the form of sickle cell anaemia. When both the parents has got sickle cell trait, some of the children will the sickle cell anaemia. So the above mentioned gene will come from both the parents. The child suffer from the disease and rarely lives a long life. The patient of sickle cell anaemia is not resistant to malaria. When he gets malaria, the anaemia will get worse and may kill the patient.
Having one copy of chromosome mutation in the hemoglobin gene will be protective against malaria and while having two copies of mutation in the hemoglobin gene will cause the individual to suffer from sickle cell anemia.