Through cell membranes. 2.3.3. Human diseases--Consistent with the diverse and critical functions of vitamin A, STRA6 mutations cause a wide spectrum of pathological phenotypes including the absence of eyes (anophthalmia), mental retardation, congenital heart defects, lung hyperplasia, intrauterine growth retardation and embryonic lethality [186, 187, 219?24]. STRA6 is the first example of a retin