Treatment Outcomes for Maple Syrup Urine Disease Detected by Newborn Screening.

OBJECTIVE: Maple syrup urine disease (MSUD), a life-threatening metabolic disorder, is included in newborn screening (NBS) programs worldwide. The study aims to evaluate the impact of NBS on the long-term outcome of MSUD patients. METHODS: We performed a prospective, national, multicenter, observational study. RESULTS: In the studied NBS cohort (N = 33; 22 classic MSUD [cMSUD], 11 variant MSUD [vMSUD]; median age at last visit 10.4 years), 32 (97%) patients survived, 58% of them had normal cognitive functions (median IQ 87). Initial peak leucine increased linearly with age in cMSUD (median: 1712 µmol/L), but not in vMSUD. Global IQ correlated inversely with the initial peak leucine concentration (P = .04; ß = -0.0081) and the frequency of decompensations (P = .02; ß = -9.133). A cluster analysis identified 2 subgroups differing in their long-term metabolic control (median leucine concentration: 162 vs 278 µmol/L; P < .001). In cMSUD, lower leucine concentrations were associated with a higher IQ (95.5 vs 80; P = .008). Liver transplantation (median age 5.8 years) was not associated with better cognitive outcome. NBS is highly sensitive for cMSUD, but vMSUD might be missed (N = 2 missed by NBS). CONCLUSIONS: NBS and the early start of treatment improve survival and long-term outcome in individuals with cMSUD. Disease severity is an important modifier of outcome; however, the time to NBS report and the quality of long-term metabolic control had an independent impact on cognitive outcome, highlighting the importance of an early diagnosis and the quality of treatment.

Gain-of-function variants in CLCN7 cause hypopigmentation and lysosomal storage disease.

Together with its ß-subunit OSTM1, ClC-7 performs 2Cl-/H+ exchange across lysosomal membranes. Pathogenic variants in either gene cause lysosome-related pathologies, including osteopetrosis and lysosomal storage. CLCN7 variants can cause recessive or dominant disease. Different variants entail different sets of symptoms. Loss of ClC-7 causes osteopetrosis and mostly neuronal lysosomal storage. A recently reported de novo CLCN7 mutation (p.Tyr715Cys) causes widespread severe lysosome pathology (hypopigmentation, organomegaly, and delayed myelination and development, "HOD syndrome"), but no osteopetrosis. We now describe two additional HOD individuals with the previously described p.Tyr715Cys and a novel p.Lys285Thr mutation, respectively. Both mutations decreased ClC-7 inhibition by PI(3,5)P2 and affected residues lining its binding pocket, and shifted voltage-dependent gating to less positive potentials, an effect partially conferred to WT subunits in WT/mutant heteromers. This shift predicts augmented pH gradient-driven Cl- uptake into vesicles. Overexpressing either mutant induced large lysosome-related vacuoles. This effect depended on Cl-/H+-exchange, as shown using mutants carrying uncoupling mutations. Fibroblasts from the p.Y715C patient also displayed giant vacuoles. This was not observed with p.K285T fibroblasts probably due to residual PI(3,5)P2 sensitivity. The gain of function caused by the shifted voltage-dependence of either mutant likely is the main pathogenic factor. Loss of PI(3,5)P2 inhibition will further increase current amplitudes, but may not be a general feature of HOD. Overactivity of ClC-7 induces pathologically enlarged vacuoles in many tissues, which is distinct from lysosomal storage observed with the loss of ClC-7 function. Osteopetrosis results from a loss of ClC-7, but osteoclasts remain resilient to increased ClC-7 activity.

Deoxyguanosine kinase deficiency: natural history and liver transplant outcome.

Autosomal recessive pathogenetic variants in the DGUOK gene cause deficiency of deoxyguanosine kinase activity and mitochondrial deoxynucleotides pool imbalance, consequently, leading to quantitative and/or qualitative impairment of mitochondrial DNA synthesis. Typically, patients present early-onset liver failure with or without neurological involvement and a clinical course rapidly progressing to death. This is an international multicentre study aiming to provide a retrospective natural history of deoxyguanosine kinase deficient patients. A systematic literature review from January 2001 to June 2023 was conducted. Physicians of research centres or clinicians all around the world caring for previously reported patients were contacted to provide followup information or additional clinical, biochemical, histological/histochemical, and molecular genetics data for unreported cases with a confirmed molecular diagnosis of deoxyguanosine kinase deficiency. A cohort of 202 genetically confirmed patients, 36 unreported, and 166 from a systematic literature review, were analyzed. Patients had a neonatal onset (≤ 1 month) in 55.7% of cases, infantile (>1 month and ≤ 1 year) in 32.3%, pediatric (>1 year and ≤18 years) in 2.5% and adult (>18 years) in 9.5%. Kaplan-Meier analysis showed statistically different survival rates (P < 0.0001) among the four age groups with the highest mortality for neonatal onset. Based on the clinical phenotype, we defined four different clinical subtypes: hepatocerebral (58.8%), isolated hepatopathy (21.9%), hepatomyoencephalopathy (9.6%), and isolated myopathy (9.6%). Muscle involvement was predominant in adult-onset cases whereas liver dysfunction causes morbidity and mortality in early-onset patients with a median survival of less than 1 year. No genotype-phenotype correlation was identified. Liver transplant significantly modified the survival rate in 26 treated patients when compared with untreated. Only six patients had additional mild neurological signs after liver transplant. In conclusion, deoxyguanosine kinase deficiency is a disease spectrum with a prevalent liver and brain tissue specificity in neonatal and infantile-onset patients and muscle tissue specificity in adult-onset cases. Our study provides clinical, molecular genetics and biochemical data for early diagnosis, clinical trial planning and immediate intervention with liver transplant and/or nucleoside supplementation.

Repurposing SGLT2 inhibitors: Treatment of renal proximal tubulopathy in Fanconi-Bickel syndrome with empagliflozin.

Renal proximal tubulopathy in Fanconi-Bickel syndrome is caused by impaired basolateral glucose transport via GLUT2 and consequently, intracellular accumulation of glucose and glycogen. SGLT2 inhibitors act on apical glucose reabsorption of renal proximal tubular cells. The purpose of this study was to retrospectively describe the first experiences with repurposing the SGLT2 inhibitor empagliflozin to treat the generalized tubulopathy in Fanconi-Bickel syndrome. A case series was conducted of seven persons from five families (five males, two females; three children, who were 14y5m, 2y9m, and 1y6m old) with genetically confirmed Fanconi-Bickel syndrome, off-label treated with empagliflozin. Median (range) age at start of empagliflozin was 27 years (1y6m - 61y) and duration of follow-up under empagliflozin treatment was 169 days (57-344). Under empagliflozin (up to 25 mg/d), biochemical parameters of tubular cell integrity (urinary N-acetyl-glucosaminidase) and/or tubular functions (including urinary α1-microglobulin) improved in all persons with Fanconi-Bickel syndrome, albeit to varying degrees. Clinically, supplementations (i.e., phosphate, alkali, carnitine, and alfacalcidol) could be completely discontinued in the three children, whereas results in the four adult patients were more variable and not as significant. Empagliflozin was well-tolerated and no symptomatic hypoglycemia was observed. In conclusion, SGLT2 inhibitors such as empagliflozin shift the metabolic block in Fanconi-Bickel syndrome, that is, they intervene specifically in the underlying pathophysiology and can thus attenuate renal proximal tubulopathy, especially when started in early childhood.

Quantification of N-acetyl-l-aspartate in dried blood spots: A simple and fast LC-MS/MS neonatal screening method for the diagnosis of Canavan disease.

BACKGROUND: Canavan disease is a devastating neurometabolic disorder caused by accumulation of N acetylaspartate in brain and body fluids due to genetic defects in the aspartoacylase gene (ASPA). New gene therapies are on the horizon but will require early presymptomatic diagnosis to be fully effective. METHODS: We therefore developed a fast and highly sensitive liquid chromatography mass spectrometry (LC-MS/MS)-based method for quantification of N-acetylaspartate in dried blood spots and established reference ranges for neonates and older controls. With this test, we investigated 45 samples of 25 Canavan patients including 8 with a neonatal sample. RESULTS: Measuring N-acetylaspartate concentration in dried blood with this novel test, all Canavan patients (with variable severity) were well separated from the control group (median; range: 5.7; 1.6-13.6 µmol/L [n = 45] vs 0.44; 0.24-0.99 µmol/L [n = 59] (p < 0.05)). There was also no overlap when comparing neonatal samples of Canavan patients (7.3; 5.1-9.9 µmol/L [n = 8]) and neonatal controls (0.93; 0.4-1.8 µmol/L [n = 784]) (p < 0.05). CONCLUSIONS: We have developed a new LC-MS/MS-based screening test for early postnatal diagnosis of Canavan disease that should be further evaluated in a population-based study once a promising treatment becomes available. The method meets the general requirements of newborn screening and should be appropriate for multiplexing with other screening approaches that combine chromatographic and mass spectrometry techniques.

Neurological outcome in long-chain hydroxy fatty acid oxidation disorders.

OBJECTIVE: This study aims to elucidate the long-term benefit of newborn screening (NBS) for individuals with long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTP) deficiency, inherited metabolic diseases included in NBS programs worldwide. METHODS: German national multicenter study of individuals with confirmed LCHAD/MTP deficiency identified by NBS between 1999 and 2020 or selective metabolic screening. Analyses focused on NBS results, confirmatory diagnostics, and long-term clinical outcomes. RESULTS: Sixty-seven individuals with LCHAD/MTP deficiency were included in the study, thereof 54 identified by NBS. All screened individuals with LCHAD deficiency survived, but four with MTP deficiency (14.8%) died during the study period. Despite NBS and early treatment neonatal decompensations (28%), symptomatic disease course (94%), later metabolic decompensations (80%), cardiomyopathy (28%), myopathy (82%), hepatopathy (32%), retinopathy (17%), and/or neuropathy (22%) occurred. Hospitalization rates were high (up to a mean of 2.4 times/year). Disease courses in screened individuals with LCHAD and MTP deficiency were similar except for neuropathy, occurring earlier in individuals with MTP deficiency (median 3.9 vs. 11.4 years; p = 0.0447). Achievement of dietary goals decreased with age, from 75% in the first year of life to 12% at age 10, and consensus group recommendations on dietary management were often not achieved. INTERPRETATION: While NBS and early treatment result in improved (neonatal) survival, they cannot reliably prevent long-term morbidity in screened individuals with LCHAD/MTP deficiency, highlighting the urgent need of better therapeutic strategies and the development of disease course-altering treatment.