The treatment for Maple Syrup Urine Disease (MSUD) consists of a hypoproteic diet with integration therapy to limit leucine intake, ensuring adequate energy, macronutrients, and micronutrients to prevent catabolism and promote anabolism. We conducted a retrospective cross-sectional study at the Metabolic Rare Disease Unit, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy. Patients with MSUD who were over 3 years old, not treated with liver transplantation, and who provided written consent, were included. The study aimed to describe the dietary treatment of patients with MSUD, evaluate growth data, and analyze the effect of a low-protein and semi-synthetic diet on body composition. Data on height, weight, BMI, waist circumference, food intake, physical activity, and DEXA scans were collected. Thirteen subjects (11 classic MSUD, 2 intermediate MSUD) were included, of which 5 < 18 years old. Results indicated that patients with MSUD follow a balanced diet and have body compositions like healthy subjects in terms of fat and lean mass. A high incidence of osteopenia was observed from a young age, with a positive correlation between protein intake and lean mass and a negative correlation between BCAA-free mixture consumption and bone mineral density z-score. The study highlights the positive effects and potential consequences of the semi-synthetic diet on the body composition of patients with MSUD. A similar study involving all Italian metabolic centers treating MSUD is recommended.

Background: Arginase 1 deficiency (ARG1-D) is an ultra-rare urea cycle disorder characterized by hyperargininemia and progressive neurological impairment, including spasticity, loss of motor function, and reduced quality of life. Conventional management based on dietary protein restriction and ammonia scavengers rarely achieves adequate metabolic control or prevents neurological deterioration. Pegzilarginase, a recombinant human arginase 1 enzyme, is the first disease-modifying therapy for ARG1-D. Methods: We report the first Italian real-world experience with pegzilarginase in three pediatric patients with genetically confirmed ARG1-D enrolled in the phase 3 PEACE trial. Clinical, biochemical, functional, nutritional and quality-of-life data were retrospectively collected over a long-term follow-up (2003–2025). Outcomes were evaluated across three phases: treatment initiation (Start), a 13-month treatment interruption due to trial closure (Stop), and therapy re-initiation through an early access program (Restart). Results: Pegzilarginase rapidly normalized plasma arginine levels and was associated with improvements in motor function, spasticity, walking endurance, dietary protein tolerance, bone mineral density, and quality of life. During treatment interruption, all patients experienced biochemical worsening and clinical deterioration, including increased spasticity, reduced mobility, and emotional distress. Re-initiation of pegzilarginase restored metabolic control and led to progressive neurological and functional recovery, including partial reversal of long-standing motor deficits. Conclusions: This real-world experience supports pegzilarginase as a disease-modifying therapy for ARG1-D. Sustained normalization of plasma arginine, rather than subthreshold biochemical control, correlates with functional and neurological improvement and may partially reverse non-lesional metabolic brain injury. Early initiation of pegzilarginase, including in newborn-screened patients, may further modify the natural history of ARG1-D.

Background/Objectives: Hereditary fructose intolerance (HFI) is a rare autosomal recessive metabolic disorder caused by variants in the ALDOB gene, resulting in aldolase B deficiency. Symptoms occur after the ingestion of fructose, sucrose, or sorbitol, leading to metabolic toxicity. Management is exclusively dietary, but clinical practice remains highly variable. This survey aimed to investigate current Italian dietary management practices for patients with HFI. Methods: A cross-sectional centre-level survey was conducted using a 29-item questionnaire distributed to metabolic dietitians within the Italian Society for the Study of Inherited Metabolic Diseases network between April and May 2026. Results: Data from 27 dietitians across 15 Italian inherited metabolic disease centres were analysed. Over half of the centres (53.3%) provided care for both paediatric and adult patients, and all centres (100%) supplied structured educational materials for the fructose-, sucrose-, and sorbitol-restricted diet. Marked heterogeneity was observed in dietary practices, particularly in the classification of sugars and sweeteners, recommendations for cereal-based products, and fibre supplementation strategies. Cereal-based dietary guidance was provided by 10/15 centres (66.7%), ranging from no specific recommendations (5/15, 33.3%) to a preference for refined grains (7/15, 46.7%) or fibre-based restrictions (2/15, 13.3%). With regard to sugars and sweeteners, consensus was observed only for maltitol and sorbitol, which were classified as prohibited by all centres (15/15, 100%). Mannitol and isomalt were prohibited in 14/15 centres (93.3%). All other compounds showed variable recommendations across centres, including xylitol (prohibited 46.7%, permitted 40.0%), erythritol (permitted 60.0%), and sucralose (prohibited 33.3%, permitted 20.0%, restricted 20.0%, unspecified 26.7%). Vitamin C (100%) and folic acid (86.6%) were the most commonly prescribed supplements. One-third (33%) of the centres required the use of fibre supplements or osmotic laxatives to manage chronic constipation, with wide variability in the specific type of fibre recommended. Conclusions: These findings highlight substantial heterogeneity in dietary management of HFI across specialised Italian centres and support the development of evidence-based, standardised nutritional guidelines to improve the consistency of care, nutritional adequacy, and patient outcomes.