Tetrahydrobiopterin deficiency is indicated at least in tetrahydrobiopterin deficiency caused by GTPCH deficiency or PTPS deficiency. This condition is very rare; approximately 600 cases have been reported worldwide. In most parts of the world, only 1% to 2% of all infants with high phenylalanine levels have this disorder. In Taiwan, about 30% of newborns with elevated levels of phenylalanine have a deficiency of THB. Subclinical deficiency can be found in individuals with poor diet (including low intake of folate or vitamin C) or genetic mutations in the MTHFR genes, which are involved in BH4 synthesis and recycling. Tetrahydrobiopterin deficiency Tetrahydrobiopterin deficiency (THBD,
Vitamin A deficiency reference point for the extent of deficiency (with mortality increasing with severity of the eye disease). In a longitudinal study of preschool Indonesian children, susceptibility to disease increased nine times when severe VAD was present. The reason for the increased infection rate in vitamin A deficient populations is the T-killer cells require retinoids to proliferate correctly. Retinoic acid binds the promoter region of specific genes, so activates the transcription process and cell replication. A vitamin A-deficient diet will have a very limited surplus of retinol, so cell proliferation and replication will be suppressed, contributing to a reduced number of T-cells