Modeling Glutaric Aciduria Type I in human neuroblastoma cells recapitulates neuronal damage that can be rescued by gene replacement.

Glutaric Aciduria type I (GA1) is a rare neurometabolic disorder caused by mutations in the GDCH gene encoding for glutaryl-CoA dehydrogenase (GCDH) in the catabolic pathway of lysine, hydroxylysine and tryptophan. GCDH deficiency leads to increased concentrations of glutaric acid (GA) and 3-hydroxyglutaric acid (3-OHGA) in body fluids and tissues. These metabolites are the main triggers of brain damage. Mechanistic studies supporting neurotoxicity in mouse models have been conducted. However, the different vulnerability to some stressors between mouse and human brain cells reveals the need to have a reliable human neuronal model to study GA1 pathogenesis. In the present work we generated a GCDH knockout (KO) in the human neuroblastoma cell line SH-SY5Y by CRISPR/Cas9 technology. SH-SY5Y-GCDH KO cells accumulate GA, 3-OHGA, and glutarylcarnitine when exposed to lysine overload. GA or lysine treatment triggered neuronal damage in GCDH deficient cells. SH-SY5Y-GCDH KO cells also displayed features of GA1 pathogenesis such as increased oxidative stress vulnerability. Restoration of the GCDH activity by gene replacement rescued neuronal alterations. Thus, our findings provide a human neuronal cellular model of GA1 to study this disease and show the potential of gene therapy to rescue GCDH deficiency.

Clinical and biochemical outcome after hydroxocobalamin dose escalation in a series of patients with cobalamin C deficiency.

BACKGROUND: CblC deficiency produces a combination of methylmalonic aciduria (MMA) and homocystinuria (HCU), and is the most common error of cobalamin metabolism. Patients present a wide spectrum of symptoms, ranging from early severe multisystemic forms, to milder late-onset phenotypes. Cognitive and visual impairment are nearly constant. Hydroxocobalamin (OHCbl), betaine, folinic acid, levocarnitine and eventually dietary protein restriction are the main therapeutic approaches. Although early introduction of OHCbl is crucial, no standardized protocols regarding dose adaptation exist. No reports on long-term outcomes after high doses of this vitamin have been published. METHODS: In this study five patients with CblC deficiency (early severe forms) were treated with high doses of OHCbl for 18 to 30months. Clinical examinations, neurological assessment, and biochemical studies (plasma total homocysteine (tHcy), amino acids, hydroxocobalamin, and methylmalonic acid in urine) were periodically performed. RESULTS: Variable clinical and biochemical outcomes were observed in patients treated with high doses of OHCbl. The best biochemical response was observed in those children with the worse metabolic control. By contrast, those patients with a concentration of tHcy around 50µmol/l or less showed only minor changes. Clinically, a considerable improvement was observed in those patients with severe problems in communication, expressive language and behavior. CONCLUSIONS: According to our study, high OHCbl doses in CblC deficiency could have a greater benefit in those children with a prior history of suboptimal metabolic control, and also in those with severe neurological phenotypes. More specifically, we observed improvements in communication skills and behavior. These results should encourage further prospective trials to determine the optimal OHCbl regimen and to generate protocols and guidelines in this rare disorder.