Back Single Gene Defects There are many different single gene defects that require clinical care by a physician or other healthcare professional. Listed in the directory below are some, for which we have provided a brief overview. Overview of Single Gene Defects Autosomal Dominant: Marfan Syndrome Autosomal Recessive: Cystic Fibrosis, Sickle Cell Anemia, Tay Sachs Disease X-linked Recessive: Red-Green Color Blindness, Hemophilia A X-linked Dominant: Incontinentia Pigmenti