However, the evidence in favour of selective tryptophan restriction remains insufficient and the consensus is evolving towards the restriction of lysine only. In the Amish community, where GA1 is overrepresented, patients with GA1 typically do not receive tryptophan-free formulas, either as the sole source of amino acids or as a supplement to protein restriction. Enhancement of precursor anabolic pathways
Lysine and hydroxylysine anabolic pathway enhancement
A possible way to prevent the build-up of metabolites is to limit lysine and hydroxylysine degradation, as lysine is one of the most abundant amino acids and tryptophan is one of the least abundant amino acids. Interaction of GCDH deficiency with vitamin C levels
Humans lack the enzyme L-gulonolactone oxidase, which is necessary for the synthesis of ascorbic acid (vitamin C), leaving them dependent on dietary sources of this vitamin. Vitamin C is a necessary cofactor for the utilization of lysine in collagen synthesis. Collagen, the most abundant protein in the human body, requires great amounts of lysine, the most abundant amino acid in proteins. Ascorbic acid, the main hydroxyl radical quencher, works as the cofactor providing the hydroxyl radical required for collagen cross-linking; lysine thus becomes hydroxylysine. GA1 worsens during stresses and catabolic episodes, such as fasts and infections. Endogenous catabolism of proteins could be an important route for glutaric acid production. It follows that collagen breakdown (and protein breakdown in general) should be prevented by all possible means. Ascorbic acid is used to prevent multiple organ failure and to lessen mortality and morbidity in intensive care units.
It thus appears reasonable to add sufficient doses of ascorbic acid to the treatment protocol during stresses and other challenges to growth in order to stimulate collagen synthesis and thus prevent lysine breakdown. Tryptophan anabolic pathway enhancement
The conversion of tryptophan to serotonin and other metabolites depends on vitamin B6. If tryptophan catabolism has any impact on brain glutaric acid and other catabolite levels, vitamin B6 levels should be routinely assayed and normalized in the course of the treatment of GA1. Management of intercurrent illnesses
Stress caused by infection, fever or other demands on the body may lead to worsening of the signs and symptoms, with only partial recovery. Prognosis
A 2006 study of 279 patients found that of those with symptoms (185, 66%), 95% had suffered an encephalopathic crises, usually with following brain damage. Of the participants in the study, 49 children died and the median age of death was 6.6 years. A Kaplan–Meier analysis of the data estimated that about 50% of symptomatic people would die by the age of 25. More recent studies provide an updated prognosis whereby individuals affected can, through proper dietary management and carnitine supplementation, manage the disease with a much improved prognosis. Newborn screening has allowed affected patients to avoid crises and live full lives without any injury to the brain. It is essential that patients with the disease be diagnosed at or before birth and that all variables be strictly managed in order to maintain quality of life.