modifies has causal genotype has causal or contributing genetic variation has manifestation Alpha Thalassemia Genotype Asymptomatic Alpha Thalassemia Trait http://bioportal.bioontology.org/ontologies/NCIT/?p=classes&conceptid=http%3A%2F%2Fncicb.nci.nih.gov%2Fxml%2Fowl%2FEVS%2FThesaurus.owl%23C95535 A condition in which a person has reduced protein production from two of the four alpha-globin alleles. -/- alpha/alpha or -/alpha -/alpha. It can exist in two forms: (1) alpha-thal-1 (alpha alpha/--), involves cis deletion of both alpha genes on the same chromosome; (2) alpha-thal-2 (alpha-/alpha-), involves trans deletion of alpha genes this occurs on different (homologous) chromosomes. SCDO:0000044 Sufficient NCIT:C95535 Alpha-Thalassemia Trait Clinical Phenotype of Beta Thalassemia Thalassemia Trait Phenotype of Sickle Cell Disease Alpha-Globin Locus Deletion