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Purpose In glycogen storage disease type III (GSD III), liver aminotransferases tend to normalize with age giving an impression that hepatic manifestations improve with age. However, despite dietary treatment, long-term liver complications emerge. We present a GSD III liver natural history study in children to better understand changes in hepatic parameters with age. Methods We reviewed clinical, biochemical, histological, and radiological data in pediatric patients with GSD III, and performed a literature review of GSD III hepatic findings. Results Twenty-six patients (median age 12.5 years, range 2–22) with GSD IIIa ( n  = 23) and IIIb ( n  = 3) were enrolled in the study. Six of seven pediatric patients showed severe fibrosis on liver biopsy (median [range] age: 1.25 [0.75–7] years). Markers of liver injury (aminotransferases), dysfunction (cholesterol, triglycerides), and glycogen storage (glucose tetrasaccharide, Glc 4 ) were elevated at an early age, and decreased significantly thereafter ( p  < 0.001). Creatine phosphokinase was also elevated with no significant correlation with age ( p  = 0.4). Conclusion Liver fibrosis can occur at an early age, and may explain the decrease in aminotransferases and Glc 4 with age. Our data outlines the need for systematic follow-up and specific biochemical and radiological tools to monitor the silent course of the liver disease process.

Molybdenum cofactor deficiency (MoCD) is an inborn error of metabolism included in the differential for refractory neonatal seizures. The prognosis is guarded, with a median reported age of death between 2.4 and 3.0 years. Mortality is primarily due to seizures and lower respiratory tract infections. MoCD has a distinct biochemical profile, characterized by elevated urinary S‐sulfocysteine, xanthine, and hypoxanthine, and low or undetectable serum and urine uric acid levels. A disease‐altering treatment is available for MoCD Type A; however, due to the rarity of the condition, its natural history remains poorly understood. We present a patient with neonatal‐onset refractory seizures, whose biochemical testing, performed within 24 h of specimen receipt in the laboratory, revealed a pattern consistent with MoCD. Before the genetics team could disclose the preliminary diagnosis, the patient demised, without evidence of worsening seizures or respiratory infection. Results of genome sequencing, guided by biochemical findings, identified double homozygous pathogenic variants in MOCS1 (associated with MoCD Type A). Although the biochemical genetics laboratory's protocol for analyzing and reporting S‐sulfocysteine levels within 48 h enabled a rapid preliminary diagnosis, the patient's condition deteriorated too quickly to initiate disease‐altering treatment, progressing more rapidly than described in the literature. We discuss potential hypotheses for his rapid decline and the broader implications for the field of biochemical genetics. Take‐Home Message As more disease‐altering treatments emerge for inborn errors of metabolism, this case underscores the urgent need for robust natural history data, faster diagnostics, and more readily available treatments, especially at large academic medical centers.

Infantile Pompe disease progresses to a lethal cardiomyopathy in absence of effective treatment. Enzyme-replacement therapy (ERT) with recombinant human acid α-glucosidase (rhGAA) has been effective in most patients with Pompe disease, but efficacy was reduced by high-titer antibody responses. Immunomodulatory gene therapy with a low dose adeno-associated virus (AAV) vector (2 × 1010 particles) containing a liver-specific regulatory cassette significantly lowered immunoglobin G (IgG), IgG1, and IgE antibodies to GAA in Pompe disease mice, when compared with mock-treated mice (P < 0.05). AAV-LSPhGAApA had the same effect on GAA-antibody production whether it was given prior to, following, or simultaneously with the initial GAA injection. Mice given AAV-LSPhGAApA had significantly less decrease in body temperature (P < 0.001) and lower anaphylactic scores (P < 0.01) following the GAA challenge. Mouse mast cell protease-1 (MMCP-1) followed the pattern associated with hypersensitivity reactions (P < 0.05). Regulatory T cells (Treg) were demonstrated to play a role in the tolerance induced by gene therapy as depletion of Treg led to an increase in GAA-specific IgG (P < 0.001). Treg depleted mice were challenged with GAA and had significantly stronger allergic reactions than mice given gene therapy without subsequent Treg depletion (temperature: P < 0.01; symptoms: P < 0.05). Ubiquitous GAA expression failed to prevent antibody formation. Thus, immunomodulatory gene therapy could provide adjunctive therapy in lysosomal storage disorders treated by enzyme replacement.

Patients with early-onset lysosomal storage diseases are ideal candidates for prenatal therapy because organ damage starts in utero. We report the safety and efficacy results of in utero enzyme-replacement therapy (ERT) in a fetus with CRIM (cross-reactive immunologic material)–negative infantile-onset Pompe’s disease. The family history was positive for infantile-onset Pompe’s disease with cardiomyopathy in two previously affected deceased siblings. After receiving in utero ERT and standard postnatal therapy, the current patient had normal cardiac and age-appropriate motor function postnatally, was meeting developmental milestones, had normal biomarker levels, and was feeding and growing well at 13 months of age. A fetus with infantile-onset Pompe’s disease was treated with a course of intrauterine enzyme replacement starting at approximately 6 months’ gestation.

Aim The urinary glucose tetrasaccharide, Glcα1‐6Glcα1‐4Glcα1‐4Glc (Glc4), is a glycogen limit dextrin that is elevated in patients with glycogen storage disease (GSD) type III. We evaluated the potential of uncooked cornstarch therapy to interfere with Glc4 monitoring, by measuring the diurnal variability of Glc4 excretion in patients with GSD III. Methods Voids were collected at home over 24 hours, stored at 4°C and frozen within 48 hours. Glc4 was analyzed using liquid chromatography‐tandem mass spectrometry and normalized to creatinine. Results Subjects with GSD III (median age: 13.5 years, range: 3.7‐62; n = 18) completed one or more 24‐hour urine collection, and 28/36 collections were accepted for analysis. Glc4 was elevated in 16/18 subjects (median: 13 mmol/mol creatinine, range: 2‐75, reference range: <3). In collections with elevated Glc4 (23/28), two‐thirds (15/23) had low diurnal variability in Glc4 excretion (coefficient of variation [CV%] <25). The diurnal variability was significantly correlated with the Glc4 concentration (Pearson R = .644, P < .05), but not with the dose of uncooked cornstarch. High intraday variability (>25%) was not consistently observed in repeat collections by the same subject. Conclusions The extent and variability of Glc4 excretion relative to creatinine was not correlated with cornstarch dose. A majority of collections showed low variability over 24 hours. These findings support the use of single time‐point collections to evaluate Glc4 in patients with GSD III treated with cornstarch. However, repeat sampling over short time‐periods will provide the most accurate assessment of Glc4 excretion, as intraday variability may be increased in patients with high Glc4 excretion.

The lack of biomarkers to identify target populations greatly limits the promise of precision medicine for major depressive disorder (MDD), a primary cause of ill health and disability. The endogenously produced molecule acetyl-L-carnitine (LAC) is critical for hippocampal function and several behavioral domains. In rodents with depressive-like traits, LAC levels are markedly decreased and signal abnormal hippocampal glutamatergic function and dendritic plasticity. LAC supplementation induces rapid and lasting antidepressant-like effects via epigenetic mechanisms of histone acetylation. This mechanistic model led us to evaluate LAC levels in humans. We found that LAC levels, and not those of free carnitine, were decreased in patients with MDD compared with age- and sex-matched healthy controls in two independent study centers. Secondary exploratory analyses showed that the degree of LAC deficiency reflected both the severity and age of onset of MDD. Moreover, these analyses showed that the decrease in LAC was larger in patients with a history of treatment-resistant depression (TRD), among whom childhood trauma and, specifically, a history of emotional neglect and being female, predicted the decreased LAC. These findings suggest that LAC may serve as a candidate biomarker to help diagnose a clinical endophenotype of MDD characterized by decreased LAC, greater severity, and earlier onset as well as a history of childhood trauma in patients with TRD. Together with studies in rodents, these translational findings support further exploration of LAC as a therapeutic target that may help to define individualized treatments in biologically based depression subtype consistent with the spirit of precision medicine.

Glycogen storage disease type Ia (GSD Ia) is a rare inherited disease caused by mutations in the glucose-6-phosphatase (G6Pase) catalytic subunit gene (G6PC). Absence of G6Pase causes life-threatening hypoglycemia and long-term complications because of the accumulations of metabolic intermediates. Bezafibrate, a pan-peroxisome proliferator-activated receptor (PPAR) agonist, was administered in the context of genome editing with a zinc-finger nuclease-containing vector (AAV-ZFN) and a G6Pase donor vector (AAV-RoG6P). Bezafibrate treatment increased survival and decreased liver size (liver/body mass, p < 0.05) in combination with genome editing. Blood glucose has higher (p < 0.05) after 4 h of fasting, and liver glycogen accumulation (p < 0.05) was lower in association with higher G6Pase activity (p < 0.05). Furthermore, bezafibrate-treated mice had increased numbers of G6PC transgenes (p < 0.05) and higher ZFN activity (p < 0.01) in the liver compared with controls. PPAR-α expression was increased and PPAR-γ expression was decreased in bezafibrate-treated mice. Therefore, bezafibrate improved hepatocellular abnormalities and increased the transduction efficiency of AAV vector-mediated genome editing in liver, whereas higher expression of G6Pase corrected molecular signaling in GSD Ia. Taken together, bezafibrate shows promise as a drug for increasing AAV vector-mediated genome editing.

Glycogen storage disease type II (Pompe disease; MIM 232300) stems from the deficiency of acid α-glucosidase (GAA; acid maltase; EC 3.2.1.20), which primarily involves cardiac and skeletal muscles. An adeno-associated virus 2/8 (AAV2/8) vector containing the muscle creatine kinase (MCK) (CK1) reduced glycogen content by ∼50% in the heart and quadriceps in GAA-knockout (GAA-KO) mice; furthermore, an AAV2/8 vector containing the hybrid α-myosin heavy chain enhancer-/MCK enhancer-promoter (MHCK7) cassette reduced glycogen content by >95% in heart and >75% in the diaphragm and quadriceps. Transduction with an AAV2/8 vector was higher in the quadriceps than in the gastrocnemius. An AAV2/9 vector containing the MHCK7 cassette corrected GAA deficiency in the distal hindlimb, and glycogen accumulations were substantially cleared by human GAA (hGAA) expression therein; however, the analogous AAV2/7 vector achieved much lower efficacy. Administration of the MHCK7-containing vectors significantly increased striated muscle function as assessed by increased Rotarod times at 18 weeks after injection, whereas the CK1-containing vector did not increase Rotarod performance. Importantly, type IIb myofibers in the extensor digitalis longus (EDL) were transduced, thereby correcting a myofiber type that is unresponsive to enzyme replacement therapy. In summary, AAV8 and AAV9-pseudotyped vectors containing the MHCK7 regulatory cassette achieved enhanced efficacy in Pompe disease mice.

Propionic acidemia (PA), arising from PCCA or PCCB variants, manifests as life-threatening cardiomyopathy and arrhythmias, with unclear pathophysiology. In this work, propionyl-CoA metabolism in rodent hearts and human pluripotent stem cell-derived cardiomyocytes was investigated with stable isotope tracing analysis. Surprisingly, gut microbiome-derived propionate rather than the propiogenic amino acids (valine, isoleucine, threonine, and methionine) or odd-chain fatty acids was found to be the primary cardiac propionyl-CoA source. In a Pcca−/−(A138T) mouse model and PA patients, accumulated propionyl-CoA and diminished acyl-CoA synthetase short-chain family member 3 impede hepatic propionate disposal, elevating circulating propionate. Prolonged propionate exposure induced significant oxidative stress in PCCA knockdown HL-1 cells and the hearts of Pcca−/−(A138T) mice. Additionally, Pcca−/−(A138T) mice exhibited mild diastolic dysfunction after the propionate challenge. These findings suggest that elevated circulating propionate may cause oxidative damage and functional impairment in the hearts of patients with PA.

ABSTRACT Purpose Enzyme replacement therapy (ERT) with recombinant human acid-α glucosidase (rhGAA) at standard dose of 20 mg/kg every other week is insufficient to halt the long-term progression of myopathy in Pompe disease. Methods We conducted a retrospective study on infantile-onset Pompe disease (IPD) and late-onset Pompe disease (LOPD) patients with onset before age 5 years, ≥12 months of treatment with standard dose ERT, and rhGAA immunogenic tolerance prior to dose escalation. Long-term follow-up of up to 18 years was obtained. We obtained physical therapy, lingual strength, biochemical, and pulmonary assessments as dose was escalated. Results Eleven patients with IPD ( n  = 7) or LOPD ( n  = 4) were treated with higher doses of up to 40 mg/kg weekly. There were improvements in gross motor function measure in 9/10 patients, in lingual strength in 6/6 patients, and in pulmonary function in 4/11. Significant reductions in urinary glucose tetrasaccharide, creatine kinase, aspartate aminotransferase, and alanine aminotransferase were observed at 40 mg/kg weekly compared with lower doses ( p  < 0.05). No safety or immunogenicity concerns were observed at higher doses. Conclusion Higher rhGAA doses are safe, improve gross motor outcomes, lingual strength, pulmonary function measures, and biochemical markers in early-onset Pompe disease, and should be considered in patients with clinical and functional decline.