BACKGROUND:Mitochondrial oxidative phosphorylation (OXPHOS) defects are clinically heterogeneous and often challenging to diagnose. Complex III deficiency caused by UQCRC2 variants is exceptionally rare, with only a limited number of patients described worldwide. Reporting new cases is essential to expand the clinical and molecular landscape of this disorder and to provide insights into potential therapeutic strategies. CASE PRESENTATION:We describe a female patient with UQCRC2-related complex III deficiency who experienced recurrent episodes of metabolic decompensation characterized by hypoglycemia, hyperlactatemia, and renal tubular dysfunction from early childhood. Brain magnetic resonance imaging revealed white matter lesions associated with mild neurological symptoms. During metabolic crises, management included intravenous glucose infusion and strict avoidance of prolonged fasting. At age 15, supplementation with coenzyme Q10 was introduced, followed by complete cessation of hospitalizations and a sustained clinical stabilization. Genetic testing identified compound heterozygosity for a known missense variant and a novel frameshift variant in UQCRC2. A literature review of previously reported cases confirmed the broad clinical variability, ranging from severe neonatal presentations to milder phenotypes with survival into adolescence. CONCLUSION:This case expands the phenotypic spectrum of UQCRC2-related complex III deficiency and suggests that targeted supplementation with coenzyme Q10 may contribute to improved longterm outcomes. Early recognition of metabolic crises, avoidance of fasting, and genetic confirmation are crucial for diagnosis and management. Further reports are needed to clarify genotype-phenotype correlations and to define the therapeutic role of coenzyme Q10 in this rare mitochondrial disorder.

OBJECTIVES:Transcobalamin II (TC) promotes the cellular uptake of cobalamin (Cbl) through receptor-mediated endocytosis of the TC-cbl complex in peripheral tissues. TC deficiency is a rare disorder that causes intracellular Cbl depletion. It presents in early infancy with a failure to thrive, diarrhea, anemia, agammaglobulinemia, and pancytopenia. Data from five TC-deficient patients including clinical, biochemical, and molecular findings, as well as long-term outcomes, were collected.CASE PRESENTATION:Mutation analysis revealed one unreported pathogenic variant in the TCN2 gene. One patient had exocrine pancreatic insufficiency. We conducted a retrospective analysis of C3 and C3/C2 from dried blood samples, as this is implemented for newborn screening (NBS). We detected a marked increase in the C3/C2 ratio in two samples. Treatment was based on parenteral Cbl. Three patients treated before six months of age had an initial favorable outcome, whereas the two treated later or inadequately had neurological impairment.CONCLUSIONS:This is the first report of Argentinean patients with TC deficiency that detected a new variant in TCN2. NBS may be a tool for the early detection of TC deficiency. This data emphasizes that TC deficiency is a severe disorder that requires early detection and long-term, aggressive therapy. Accurate diagnosis is imperative, because early detection and treatment can be life-saving.

Objective: To characterize adherence to Phenylketonuria (PKU) management practices among PKU patients treated at reference sites around Argentina, Brazil, and Mexico.Methods: This is a retrospective, observational, multicenter, and multinational survey-based study using aggregate data. From an initial list of 40 sites, 22 clinicians expressed interest in completing the survey, with 20 clinicians from 20 unique sites fulfilling all the study criteria. The Survey contained 28 questions, including respondent's clinic characteristics, clinic PKU treatment recommendations, and patient adherence to clinic recommendations. Survey was available in local languages, and the respondents were asked to consult their clinic records to complete their responses. Adherence was assessed by target blood phenylalanine (Phe), target blood testing frequency, and clinic visits.Results: A total of 1077 (out of 1377) actively managed PKU patients (seen in the clinic in the last 3 years) from 13 clinics in Brazil, six in Argentina, and one in Mexico were analyzed. Upper blood Phe target was set over 360 mu Mol/L in 70% of the clinics for adult patients. Around 40% of the patients >30 years old had Phe blood tests done twice a year or less, with 60% of the clinics recommending semestral visits for adults <30 years old. Twice a month was the most common frequency of visits for <1 year old. The COVID-19 pandemic was a disruptor for frequency of visits and exams.Conclusions: These results show that there is still room for improvement in terms of adherence, namely in adults and older children. More efforts must be made to educate patients and healthcare professionals about the importance of treatment adherence, accompanied by public policies that expand access to pharmacological and dietary treatment with diversity and quality to improve adherence to adequate blood Phe levels.

Hyperammonemia is a medical emergency. There are no publications regarding the availability of resources, supplies, and knowledge necessary for the initial management of hyperammonemia by pediatricians in Argentina; however, according to the authors' experience, the necessary resources are not available all year round in a large portion of our territory. Based on such state of affairs, an international bibliographic review on this topic and the authors' experience, we developed a series of recommendations for the initial pediatric management of this emergency, with the objective of reducing deficiencies, allowing adequate clinical suspicion leading to a timely diagnosis and emergency management and a rational use of pharmacological resources (some of which are costly) to reduce the morbidity and mortality associated with hyperammonemia.

Considering the advances made on mucopolysaccharidosis type I after the consensus study published by a group of experts in Argentina in 2008, recommendations about genetic testing, cardiological follow-up, airway care, hearing impairment detection, spinal and neurological conditions, as well as current treatments, were reviewed. Emphasis was placed on the need for early diagnosis and treatment, as well as an interdisciplinary follow-up.

Here we describe the current challenges of mucopolysaccharidosis type I: the need for an adequate classification, establishing its relationship to therapeutic indications; an early diagnosis, from neonatal screening, its advantages and barriers, to clinical suspicion of severe and attenuated forms; spinal and eye disease care, from diagnosis to follow-up and treatment; allergic reactions caused by enzyme replacement therapy, their diagnosis and treatment. And lastly, transition to adult care.

Considering the advances made on mucopolysaccharidosis type I after theconsensus study published by a group of experts in Argentina in 2008, recommendations about genetic testing, cardiological follow-up, airway care, hearing impairment detection, spinal and neurological conditions, as well as current treatments, were reviewed. Emphasis was placed on the need for early diagnosis and treatment, as well as an interdisciplinary follow-up.

Here we describe the current challenges of mucopolysaccharidosis type I: the need for an adequate classification, establishing its relationship to therapeutic indications; an early diagnosis, from neonatal screening, its advantages and barriers, to clinical suspicion of severe and attenuated forms; spinal and eye disease care, from diagnosis to follow-up and treatment; allergic reactions caused by enzyme replacement therapy, their diagnosis and treatment. And lastly, transition to adult care.Se describen como desafíos actuales en mucopolisacaridosis I la necesidad de una clasificación adecuada, vinculándola a las indicaciones terapéuticas; el diagnóstico temprano desde la pesquisa neonatal, sus ventajas y dificultades hasta la sospecha clínica de las formas grave y atenuada; el cuidado de la patología espinal y oftalmológica, desde el diagnóstico, el seguimiento y el tratamiento; las reacciones alérgicas por terapia de reemplazo enzimático, su diagnóstico y tratamiento. Por último, la transición hacia el cuidado adulto.

BACKGROUND:Classical galactosemia is an autosomal recessive inherited metabolic disorder caused by mutations in the galactose-1-phosphate uridyltransferase (GALT) gene. GALT enzyme deficiency leads to the accumulation of galactose-1-phosphate in various organs, causing hepatic, renal and cerebral impairment. Over 300 mutations have been reported in the GALT gene. The aim of this study was to describe molecular characterization of GALT gene in Argentinian patients with decreased GALT activity, and to correlate molecular results with enzyme activity. METHODS:37 patients with enzyme activity below 6.3 μmol/h/g Hb (35% of normal value) were included. GALT activity was measured on red blood cells. DNA was extracted from peripheral blood. p.Gln188Arg mutation was studied by PCR-RFLP and, on samples negative or heterozygous, GALT gene was sequenced. In vivo splicing analysis of the GALT gene was performed on RNA extracted from leukocytes of one patient. RESULTS:14 different sequence variations were identified among 72 unrelated alleles. The two most common disease-causing mutations were p.Gln188Arg (24/72) and p.Lys285Asn (9/72). Three novel mutations were detected. One of them, c.688G>A, caused partial skipping of exon 9 of the GALT gene. Enzyme activity correlated with GALT genotype in 36 of the 37 patients. CONCLUSION:This is the first report of sequence variations in the GALT gene in the Argentinian population. This study highlights the contribution of the molecular analysis to the diagnosis of Galactosemia and reveals c.688G>A as a novel Duarte-like variant, with a high prevalence in our population.

Pompe disease, also known as acid maltase deficiency or glycogenosis type II, is a rare severe, autosomal, recessive, and progressive genetic disorder caused by deficiency in alphaglucosidase.The classic infantile-onset is the most broadly known form of Pompe disease, which presents with severe heart involvement and clear hypotonia, while the non-classic presentation occurs with early motor involvement.Late-onset Pompe disease develops in adults, but it may also occur during childhood or adolescence.Here we update the available clinical and diagnostic findings because an early management with enzyme replacement therapy may improve patients' survival and quality of life.We also review the benefits and adverse effects of available treatments and new lines of therapeutic research.

Mitochondrial dysfunction represents an important cellular stressor and when intense and persistent cells must unleash an adaptive response to prevent their extinction. Furthermore, mitochondria can induce nuclear transcriptional changes and DNA methylation can modulate cellular responses to stress. We hypothesized that mitochondrial dysfunction could trigger an epigenetically mediated adaptive response through a distinct DNA methylation patterning. We studied cellular stress responses (i.e., apoptosis and autophagy) in mitochondrial dysfunction models. In addition, we explored nuclear DNA methylation in response to this stressor and its relevance in cell survival. Experiments in cultured human myoblasts revealed that intense mitochondrial dysfunction triggered a methylation-dependent pro-survival response. Assays done on mitochondrial disease patient tissues showed increased autophagy and enhanced DNA methylation of tumor suppressor genes and pathways involved in cell survival regulation. In conclusion, mitochondrial dysfunction leads to a “pro-survival” adaptive state that seems to be triggered by the differential methylation of nuclear genes.

Citrullinemia type I is an autosomal recessive disorder caused by mutation of the gene expressing ASS1 argininosuccinate synthetase, limiting enzyme of the urea cycle.The classic variants are associated with neonatal/infantile forms that cause hyperammonemia leading to death if treatment is not established.Initial symptoms of disorders of the urea cycle include neurological impairment with mild or moderate liver damage. We report a case of recurrent liver failure in an infant diagnosed with type I citrullinemia without severe neurological involvement that was referred to our center for liver transplantation.Acute liver failure can be caused by a wide range of disorders in which inborn errors of metabolism are included. Appropriate treatment of disorders of the urea cycle and in particular citrullinemia I can avoid the need for a transplant.

Presentación de casos clínicos RESUMENLa citrulinemia tipo I es un desorden autosómico recesivo causado por la mutación del gen ASS1, que expresa argininosuccinato sintetasa, enzima limitante del ciclo de la urea.Las variantes clásicas están asociadas con la forma neonatal/ infantil, que llevan a hiperamoniemia y a la muerte si el tratamiento no es instaurado.Los síntomas iniciales de los trastornos del ciclo de la urea incluyen deterioro neurológico con leve o moderado daño hepático.Reportamos un caso de falla hepática recurrente en un lactante con diagnóstico de citrulinemia tipo I sin compromiso neurológico grave, que fue derivado a nuestro centro para trasplante hepático.La falla hepática aguda puede ser causada por una gran variedad de desórdenes, dentro de los que se incluyen errores congénitos del metabolismo.El tratamiento adecuado de los trastornos del ciclo de la urea y, en particular, la citrulinemia I puede evitar la necesidad de un trasplante.