A 10-year-old Lebanese Arab girl had vitamin A deficiency as evidenced by night blindness, bilateral Bitot's spots, and very low plasma vitamin A concentration (7μg/100 ml). Total plasma carotenoid values were high with about 50% as β-carotene. Repeated blood sampling after large doses of β-carotene failed to produce any retinyl ester in the plasma whereas there was significant rise of ester levels in three control subjects. Preformed vitamin A cured the clinical condition and caused retinyl ester to appear in the plasma. There was no malabsorption, hypothyroidism, or liver dysfunction. The evidence suggests failure of enzymic conversion of β-carotene to retinal in the intestine as the cause of vitamin A deficiency.
McLaren DS, Zekian B. Failure of Enzymic Cleavage of β-CaroteneThe Cause of Vitamin A Deficiency in a Child. Am J Dis Child. 1971;121(4):278–280. doi:10.1001/archpedi.1971.02100150052002