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INTRODUCTION: Tyrosinemia type 1 is a rare disease with autosomal recessive inheritance, featuring various clinical manifestations. These may encompass acute neonatal liver failure, neonatal cholestatic syndrome, chronic hepatitis, cirrhosis, hepatocellular carcinoma, and, alternatively, kidney disorders like renal tubular acidosis, Fanconi syndrome, hypophosphatemic rickets, among other alterations. Diagnosis relies on detecting toxic metabolites in the blood and urine, ideally confirmed through molecular testing. METHOD: A consensus was reached with experts in the field of inborn errors of metabolism (EIM), including eight pediatric gastroenterologists, two EIM specialists, two geneticists, three pediatric nutritionists specialized in EIM, and a pediatric surgeon specializing in transplants. Six working groups were tasked with formulating statements and justifications, and 32 statements were anonymously voted on using the Likert scale and the Delphi method. The first virtual vote achieved an 80% consensus, with the remaining 20% determined in person. RESULTS: The statements were categorized into epidemiology, clinical presentation, diagnosis, nutritional and medical treatment, and genetic counseling. CONCLUSIONS: This consensus serves as a valuable tool for primary care physicians, pediatricians, and pediatric gastroenterologists, aiding in the prompt diagnosis and treatment of this disease. Its impact on the morbidity and mortality of patients with tyrosinemia type 1 is substantial.

INTRODUCCIÓN: La tirosinemia tipo 1 es una enfermedad rara, con herencia autosómica recesiva, con múltiples manifestaciones clínicas, que pueden comprender desde falla hepática aguda neonatal, síndrome colestásico neonatal, hepatitis crónica, cirrosis o hepatocarcinoma, hasta alteraciones renales como acidosis tubular renal, síndrome de Fanconi o raquitismo hipofosfatémico, entre otras. El diagnóstico se basa en la presencia de metabolitos tóxicos en la sangre y la orina, idealmente con la confirmación molecular de la enfermedad. MÉTODO: Se realizó un consenso con expertos en el área de los errores innatos del metabolismo (EIM): ocho gastroenterólogos pediatras, dos médicos especialistas en EIM, dos genetistas, tres nutriólogas pediatras especializadas en EIM y un cirujano pediatra especialista en trasplantes. Se formaron seis mesas de trabajo encargadas de desarrollar los enunciados con sus justificaciones y fueron votados anónimamente 32 enunciados en una escala Likert con un método Delphi. La primera votación fue virtual, obteniendo consenso del 80% de los enunciados, y la segunda fue presencial, obteniendo el 20% restante. RESULTADOS: Los enunciados fueron divididos en epidemiología, cuadro clínico, diagnóstico, tratamiento nutricional y médico, y consejo genético. CONCLUSIONES: Este consenso constituye una valiosa herramienta para los médicos de atención primaria, pediatras y gastroenterólogos pediátricos, ya que ayuda a diagnosticar y tratar rápidamente esta enfermedad. Su impacto en la morbilidad y mortalidad de los pacientes con tirosinemia tipo 1 es sustancial.

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Advances in an early diagnosis by expanded newborn screening (NBS) have been achieved mainly in developed countries, while populations of middle- and low-income countries have poor access, leading to disparities. Expanded NBS in Mexico is not mandatory. Herein, we present an overview of the differences and unmet NBS needs of a group of Mexican patients with inborn errors of intermediary metabolism (IEiM), emphasizing the odyssey experienced to reach a diagnosis. We conducted a retrospective observational study of a historical cohort of patients with IEiM from a national reference center. A total of 924 patients with IEiM were included. Although 72.5% of the diseases identified are detectable by expanded NBS, only 35.4% of the patients were screened. The mortality in the unscreened group was almost two-fold higher than that in the screened group. Patients experienced a median diagnostic delay of 4 months, which is unacceptably long considering that to prevent disability and death, these disorders must be treated in the first days of life. Patients had to travel long distances to our reference center, contributing to their unacceptable diagnostic odyssey. This study highlights the urgent need to have an updated, expanded NBS program with adequate follow up in Mexico and promote the creation of regional medical care centers. We also provide compelling evidence that could prove valuable to decision makers overseeing public health initiatives for individuals impacted by IEiM from middle- and low-income countries.

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BACKGROUND: Newborn screening for glucose-6-phosphate dehydrogenase deficiency (G6PDd) was implemented in Mexico beginning in 2017. In a Mexican population, genotyping analysis of G6PD as a second-tier method identified a previously unreported missense variant, p.(Ser184Cys), which we propose to call "Toluca", and the extremely rare p.(Gln195His) or "Tainan" variant, which was previously described in the Taiwanese population as a Class II allele through in silico evaluations. Here, we sought to perform in vitro biochemical characterizations of the Toluca and Tainan G6PD natural variants and describe their associated phenotypes. METHODS: The "Toluca" and "Tainan" variants were identified in three unrelated G6PDd newborn males, two of whom lacked evidence of acute hemolytic anemia (AHA) or neonatal hyperbilirubinemia (NHB). We constructed wild-type (WT), Tainan, and Toluca G6PD recombinant enzymes and performed in vitro assessments. RESULTS: Both variants had diminished G6PD expression, decreased affinities for glucose-6-phosphate and NADP+ substrates, significant decreases in catalytic efficiency (∼97 % with respect to WT-G6PD), and diminished thermostabilities that were partially rescued by NADP+. In silico protein modeling predicted that the variants would have destabilizing effects on the protein tertiary structure, potentially reducing the enzyme half-lives and/or catalytic efficiencies. CONCLUSION: Our data suggest that G6PD "Tainan" and "Toluca" are potential Class II natural variants, which agrees with the absence of chronic nonspherocytic hemolytic anemia (CNSHA) in our patients. It remains to be determined whether these variants represent high-risk genetic factors for developing CNSHA, AHA, and/or NHB.

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Establishing the genotypes of patients with hyperphenylalaninemia (HPA)/phenylketonuria (PKU, MIM#261600) has been considered a cornerstone for rational medical management. However, knowledge of the phenylalanine hydroxylase gene (PAH) mutational spectrum in Latin American populations is still limited. Herein, we aim to update the mutational PAH spectrum in the largest cohort of HPA/PKU Mexican patients (N = 124) reported to date. The biallelic PAH genotype was investigated by Sanger automated sequencing, and genotypes were correlated with documented biochemical phenotypes and theoretical tetrahydrobiopterin (BH4) responsiveness. Patients were biochemically classified as having classic PKU (50%, 62/124), mild PKU (20.2%, 25/124) and mild HPA (29.8%, 37/124). Furthermore, 78.2% of the included patients (97/124) were identified by newborn screening. A total of 60 different pathogenic variants were identified, including three novel ones (c. 23del, c. 625_626insC and c. 1315 + 5_1315 + 6insGTGTAACAG), the main categories being missense changes (58%, 35/60) and those affecting the catalytic domain (56.6%, 34/60), and c. 60 + 5G > T was the most frequent variant (14.5%, 36/248) mainly restricted (69.2%) to patients from the central and western parts of Mexico. These 60 types of variants constituted 100 different biallelic PAH genotypes, with the predominance of compound-heterozygous ones (96/124, 77%). The expected BH4 responsiveness based on the PAH genotype was estimated in 52% of patients (65/124), mainly due to the p. (Val388Met) (rs62516101) allele. Instead, our study identified 27 null variants with an allelic phenotype value of zero, with a predominance of c. 60 + 5G > T, which predicts the absence of BH4 responsiveness. An identical genotype reported in BIOPKUdb was found in 92/124 (74%) of our patients, leading to a genotype-phenotype concordance in 80/92 (86.9%) of them. The high number of variants found confirms the heterogeneous and complex mutational landscape of HPA/PKU in Mexico.

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BACKGROUND: Glucose-6-phosphate dehydrogenase deficiency (G6PDd) newborn screening is still a matter of debate due to its highly heterogeneous birth prevalence and clinical expression, as well as, the lack of enough knowledge on its natural history. Herein, we describe the early natural clinical course and the underlying GDPD genotypes in infants with G6PDd detected by newborn screening and later studied in a single follow-up center. G6PDd newborns were categorized into three groups: group 1: hospitalized with or without neonatal jaundice (NNJ); group 2: non-hospitalized with NNJ; and group 3: asymptomatic. Frequencies of homozygous UGT1A1*28 (rs34983651) genotypes among G6PDd patients with or without NNJ were also explored. RESULTS: A total of 81 newborns (80 males, one female) were included. Most individuals (46.9%) had NNJ without other symptoms, followed by asymptomatic (42.0%) and hospitalized (11.1%) patients, although the hospitalization of only 3 of these patients was related to G6PDd, including NNJ or acute hemolytic anemia (AHA). Nine different G6PDd genotypes were found; the G6PD A-202A/376G genotype was the most frequent (60.5%), followed by the G6PD A-376G/968C (22.2%) and the Union-Maewo (rs398123546, 7.4%) genotypes. These genotypes produce a wide range of clinical and biochemical phenotypes with significant overlapping residual enzymatic activity values among class I, II or III variants. Some G6PD A-202A/376G individuals had enzymatic values that were close to the cutoff value (5.3 U/g Hb, 4.6 and 4.8 U/g Hb in the groups with and without NNJ, respectively), while others showed extremely low enzymatic values (1.1 U/g Hb and 1.4 U/g Hb in the groups with and without NNJ, respectively). Homozygosity for UGT1A1*28 among G6PDd patients with (11.9%, N = 5/42) or without (10.3%, N = 4/39) NNJ did not shown significant statistical difference (p = 0.611). CONCLUSION: Wide variability in residual enzymatic activity was noted in G6PDd individuals with the same G6PD genotype. This feature, along with a documented heterogeneous mutational spectrum, makes it difficult to categorize G6PD variants according to current WHO classification and precludes the prediction of complications such as AHA, which can occur even with > 10% of residual enzymatic activity and/or be associated with the common and mild G6PD A-376G/968C and G6PD A-202A/376G haplotypes.

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Abstract Introduction: Any abnormal newborn screening (NBS) test should be subjected to appropriate diagnostic tests and should be followed. Once the newborn has been diagnosed and treated, the family should receive comprehensive genetic services. Aim: To present the experience of studying older siblings of patients with inborn errors of metabolism (IEM) identified by NBS in a single-national follow-up reference center. Methods: A retrospective analysis of medical files of the IEM patients detected by NBS was conducted. All those older siblings who tested positive for the same IEM of the patient detected by newborn screening were included. Results: A total of 26 positive siblings from 18 families with seven different IEM were found (phenylketonuria, argininemia, glucose-6-phosphate dehydrogenase deficiency, 3-methylcrotonyl-CoA carboxylase deficiency, dihydropteridine reductase deficiency, tyrosinemia type 3, and medium chain acyl-CoA dehydrogenase deficiency). The age range of the affected siblings was 2 to 19 years old, with a mean age of 8.5 years. Ten older siblings (38.5%) had clinical consequences for the disease, including severe intellectual disability. Conclusions: It is necessary to study older siblings, and family history and genetic counseling of all NBS-detected families should be recommended, especially in countries where expanded NBS programs are beginning.

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BACKGROUND: Tyrosinemia type 1 (HT1, MIM#276700) is caused by a deficiency in fumarylacetoacetate hydrolase (FAH) and it is associated with severe liver and renal disfunction. At present, the mutational FAH (15q25.1, MIM*613871) spectrum underlying HT1 in the Mexican population is unknown. The objective of this study was to determine the FAH genotypes in eight nonrelated Mexican patients with HT1, who were diagnosed clinically. METHODS: Sequencing of FAH and their exon-intron boundaries and in silico protein modeling based on the crystallographic structure of mouse FAH. RESULTS: We identified pathogenic variants in 15/16 studied alleles (93.8%). Nine different variants were found. The most commonly detected HT1-causing allele was NM_000137.2(FAH):c.3G > A or p.(?) [rs766882348] (25%, n = 4/16). We also identified a novel missense variant NM_000137.2(FAH):c.36C > A or p.(Phe12Leu) in a homozygous patient with an early and fatal acute form. The latter was classified as a likely pathogenic variant and in silico protein modeling showed that Phe-12 residue substitution for Leu, produces a repulsion in all possible Leu rotamers, which in turn would lead to a destabilization of the protein structure and possible loss-of-function. CONCLUSION: HT1 patients had a heterogeneous mutational and clinical spectrum and no genotype-phenotype correlation could be established.

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Maple syrup urine disease (MSUD) is a metabolic disorder caused by mutations in three of the branched-chain α-keto acid dehydrogenase complex (BCKDC) genes. Classical MSUD symptom can be observed immediately after birth and include ketoacidosis, irritability, lethargy, and coma, which can lead to death or irreversible neurodevelopmental delay in survivors. The molecular diagnosis of MSUD can be time-consuming and difficult to establish using conventional Sanger sequencing because it could be due to pathogenic variants of any of the BCKDC genes. Next-generation sequencing-based methodologies have revolutionized the molecular diagnosis of inborn errors in metabolism and offer a superior approach for genotyping these patients. Here, we report an MSUD case whose molecular diagnosis was performed by clinical exome sequencing (CES), and the possible structural pathogenic effect of a novel E1α subunit pathogenic variant was analyzed using in silico analysis of α and ß subunit crystallographic structure. Molecular analysis revealed a new homozygous non-sense c.1267C>T or p.Gln423Ter variant of BCKDHA. The novel BCKDHA variant is considered pathogenic because it caused a premature stop codon that probably led to the loss of the last 22 amino acid residues of the E1α subunit C-terminal end. In silico analysis of this region showed that it is in contact with several residues of the E1ß subunit mainly through polar contacts, hydrogen bonds, and hydrophobic interactions. CES strategy could benefit the patients and families by offering precise and prompt diagnosis and better genetic counseling.

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BACKGROUND: Tetrahydrobiopterin (BH4) is the cofactor for 6-pyruvoyl-tetrahydropterin synthase (PTPS); it is involved in BH4 biosynthesis and is encoded by PTS gene. Its deficiency (PTPSD) is characterized by hyperphenylalaninemia (HPA) and deficit in central monoamine neurotransmitters. We describe the clinical and mutational spectrum of five patients with PTPSD, from four unrelated Mexican families. All patients had symptomatic diagnosis and presented severe early neurological manifestations and HPA. METHODS: Clinical and biochemical data from studied patients were recorded. Responsible PTPSD genotypes was determined by direct and bidirectional Sanger DNA sequencing of the six PTS coding exons and their exon-intron borders, and these were directly searched in the available relatives. The novel PTS missense variant [NM_3000317.2:331G > T, p.(Ala111Ser)] was subjected to in silico, to predict a possible deleterious effect. RESULTS: Diminished fetal movements were perceived as a uniform characteristic in the studied group. DNA sequencing showed two known p.(Arg25∗) and p.(Val132TyrFs∗19) and the novel missense p.(Ala111Ser) PTS variants, the latter representing potentially a frequent PTPSD-responsible allele (50%, 4/8) in Mexican patients. In silico protein modeling analysis of the p.(Ala111Ser) variant revealed loss of hydrophobic interactions between the alanine and neighboring valines, suggesting that these changes in polarity may be detrimental for enzyme function, structure and/or stability. CONCLUSIONS: This work contributes to the knowledge of PTPS molecular spectrum. The delayed diagnosis of these patients emphasizes the importance of considering BH4 metabolism defects in the differential diagnosis of HPA, especially for countries that are beginning their HPA newborn screening programs.

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Ornithine transcarbamylase deficiency (OTCD) is an X-linked urea cycle defect associated with severe and usually fatal hyperammonemia. This study describes a patient with early onset lethal OTCD due to a known pathogenic variant (c.298+1G>A), as well as the novel autopsy finding of kernicterus with relatively low blood concentration of unconjugated bilirubin (UCB) (11.55 mg/dL). The patient was a full-term male with a family history of two previous male siblings who died as newborns after acute neurologic deterioration. The patient's symptoms began at 24 h of life with lethargy that rapidly progressed to coma upon admission to the neonatal intensive care unit. Although hyperammonemia and hyperbilirubinemia were documented, hemofiltration could not be performed. OTCD diagnosis was biochemically established. Despite nutritional intervention and treatment for hyperammonemia, the patient died on the sixth day of life. At autopsy, external brain examination revealed a marked yellow pigmentation typical of kernicterus that included gray matter, particularly the thalamus and basal ganglia; dentate nuclei of the cerebellum and brain stem gray matter were also affected. Microscopic findings were consistent with the classical description of tissue damage in OTCD, including the presence of Alzheimer type II astrocytes in basal ganglia, necrosis, neuronal loss with spongiform degeneration and macrophage infiltration surrounded by astroglia. This condition may be an important comorbidity in newborns with hyperammonemia.

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Hepatorenal tyrosinemia is a treatable metabolic disease characterized by progressive liver failure, renal damage and pronounced coagulopathy. Its clinical diagnosis is difficult because of its low prevalence and heterogeneous symptoms. In developed countries, expanded newborn screening, based on succinylacetone quantification by tandem mass spectrometry, has been very valuable in the early detection of hepatorenal tyrosinemia, providing the opportunity for rapid treatment of affected patients. In developing countries without systematic expanded newborn screening, however, diagnosis and treatment of this disease remain major challenges, as genetic diseases in these countries are not a health priority and there are few referral centers for infants with inherited errors of metabolism. This chapter describes the diagnosis, follow-up and outcome of 20 Mexican patients with hepatorenal tyrosinemia. This chapter also constitutes a call to action to pediatricians, gastroenterologists, geneticists and other health professionals, and to academic organizations, health authorities and patient advocacy groups, to promote early patient detection and treatment, reducing the unacceptably high mortality rate (75%) in Mexican infants with this potentially deadly but eminently treatable condition.

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INTRODUCTION: Hepatorenal tyrosinemia (HT1) is a treatable, inherited, metabolic disease characterized by progressive liver failure with pronounced coagulopathy. The aim of this study is to describe the clinical, biochemical, and histopathological findings in a group of Mexican HT1 patients and their outcome. MATERIAL AND METHODS: Medical records of HT1 patients diagnosed between 1995 and 2011 were analyzed. The diagnosis of HT1 was confirmed by detection of succinylacetone in urine or blood. RESULTS: Sixteen nonrelated HT1 cases were analyzed. Mean age at clinical onset was 9 months, and the mean age at diagnosis was 16.3 months. Main clinical findings were hepatomegaly, splenomegaly, cirrhosis, liver failure, tubulopathy, nephromegaly, Fanconi syndrome, seizures and failure to thrive. Histopathological findings were cirrhosis, fibrosis and steatosis. The HT1 group had a mortality rate of 78%. Patients who received supportive care or nutritional treatment had a 3-year survival rate of 10%. For those who underwent liver transplantation, the 6-year survival rate was 60%. In most cases pharmacological treatment with nitisinone and special dietary products were not available. The leading causes of death were fulminant liver failure, metastatic hepatocellular carcinoma, and porphyria-like neurologic crisis. Newborn screening programs in combination with the availability of orphan drugs, proper monitoring, genetic counseling, and clinical practice guidelines are needed to enable physicians to identify the disease, delay its progression, and improve patients' quality of life. CONCLUSION: The devastating natural history of HT1 is still observed in Mexican patients because they are not diagnosed and treated during the early stages of the disease.

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Classic nephropathic cystinosis (CNC) is an autosomal recessive and infrequent inborn metabolic disease that should be suspected in all children who show failure to thrive and renal Fanconi syndrome (RFS). Slit-lamp examination reveals pathognomonic corneal deposits of cystine crystals in virtually all affected individuals after 12-16 mo of age. A diagnosis of CNC is difficult to confirm in children living in Mexico and most Latin American countries, because cystine levels can be measured only at a few locations. We report the cystinosin genotype findings in 15 Latin American patients with a high clinical suspicion of CNC mainly due to RFS (n =13), although five of them lacked proper ophthalmologic assessment, despite being more than 1-year-old. Molecular analysis confirmed diagnosis of CNC in six (40%) of the 15 patients, five of them with RFS and cystine crystals. The remaining nine (60%) patients had a normal genotype. The predominance of a normal cystinosin genotype in eight of 13 patients with RFS (61.50%) reinforces the need to perform slit-lamp examinations in all patients with RFS over 1 yr of age, prior to measuring cystine or performing molecular cystinosin study, both methods not readily available throughout Latin America.

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OBJECTIVE: Identify CTNS gene mutations in nephropathic cystinosis Mexican patients. SUBJECTS AND METHODS: Eleven patients were included, nine presenting infantile nephropathic cystinosis and two siblings with the juvenile phenotype. The common 57-kb deletion was detected by multiplex PCR using large deletion marker-2 (LDM-2)/exon 4 set primers. Those alleles negative for 57-kb deletion were screened by single strand confirmation polymorphism (SSCP) and subsequent direct sequencing. RESULTS: In our sample, five mutations previously reported are identified: 57-kb deletion, EX4_EX5del, c.985_986insA, c.357_360delGACT, and c.537_557del. We detect a false assignation of 57-kb deletion homozygous genotype by using the LDM-2/exon 4 primers. In addition, four novel and severe mutations are identified: c.379delC, c.1090_1093delACCAinsCG, c.986C>G (p.T216R), and c.400+5G>A. CONCLUSIONS: Our sample of Mexican patients display allelic heterogeneity as compared to European or North American cystinosis cases. The identification of novel mutations might suggest the presence of exclusive American CTNS alleles in Mexican population. In order to prevent the false positive assignation of 57-kb deletion genotype, as caused by the presence of another type of intragenic CTNS gross deletion, we propose to analyze a different control CTNS exon to those originally reported in both LDM multiplex PCR assays, especially when parental DNA samples are not available.

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INTRODUCTION: Maple syrup urine disease (MSUD) is a genetic disorder that produces ketoacidosis crises and neurological complications often leading to death. The age of diagnosis and treatment determine a child's adequate and healthy outcome. OBJECTIVE: Describe the characteristics of a pediatric Mexican cohort with MSUD. MATERIAL AND METHODS: Retrospective analysis of MSUD cases seen at our Metabolic Unit between 1991- 2006. RESULTS: We studied 36 patients; three were initially detected through neonatal screening, one of them done in Mexico and two in the United States. The latter were given timely treatment and developed normally, both intellectually and physically. The patient detected in Mexico was not given adequate treatment and died at 3 months of age. The remaining 33 patients were diagnosed between 2-24 months using standard biochemical tests performed after symptoms became noticeable. All symptomatic patients had high levels of branched-chain amino acids. Hypotonia, refusal to eat and seizures were the most frequent symptoms. The cohort's mortality was 50% (18/36), while 81.2% (13/18) of survivors displayed cognitive impairment. DISCUSSION: Mexico needs a comprehensive treatment protocol for the care of MSUD patients including newborn screening, early treatment, follow-up and genetic counseling.

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Introducción: La enfermedad de jarabe de arce es una enfermedad genética que produce crisis de cetoacidosis y deterioro neurológico progresivo que llevan a un coma fatal. El inicio del tratamiento temprano es determinante en el pronóstico. Objetivo: Describir las características de una cohorte de pacientes mexicanos con enfermedad de orina con olor a jarabe de arce (EOJA). Material y métodos: Se hizo un análisis retrospectivo de casos de EOJA de 1991 a 2006. Resultados: Encontramos 36 pacientes (16 niñas y 20 niños). Tres fueron inicialmente detectados mediante tamiz neonatal, uno de ellos realizado en México y los otros dos en el extranjero. Estos últimos recibieron tratamiento oportuno y exhiben desarrollo psicomotor normal. El caso detectado en México no recibió tratamiento adecuado y falleció. Los otros 33 pacientes se diagnosticaron entre los 2 y los 73 meses de edad mediante tamiz metabólico (postsintomático) ante la sospecha clínica. Todos los pacientes sintomáticos presentaron resultado positivo a la prueba de dinitrofenilhidrazina y aminoácidos ramificados elevados. La hipotonía, rechazo al alimento, y las crisis convulsivas fueron los síntomas más frecuentes. En esta cohorte, la mortalidad fue del 50 % (18/36) y el 81.2 % de los sobrevivientes (13/18) muestran actualmente retraso psicomotor. Discusión: Es necesario establecer en México un modelo de atención integral para la EOJA que incluya la detección presintomática preventiva, el tratamiento temprano, el seguimiento y asesoramiento genético.

INTRODUCTION: Maple syrup urine disease (MSUD) is a genetic disorder that produces ketoacidosis crises and neurological complications often leading to death. The age of diagnosis and treatment determine a child's adequate and healthy outcome. OBJECTIVE: Describe the characteristics of a pediatric Mexican cohort with MSUD. MATERIAL AND METHODS: Retrospective analysis of MSUD cases seen at our Metabolic Unit between 1991- 2006. RESULTS: We studied 36 patients; three were initially detected through neonatal screening, one of them done in Mexico and two in the United States. The latter were given timely treatment and developed normally, both intellectually and physically. The patient detected in Mexico was not given adequate treatment and died at 3 months of age. The remaining 33 patients were diagnosed between 2-24 months using standard biochemical tests performed after symptoms became noticeable. All symptomatic patients had high levels of branched-chain amino acids. Hypotonia, refusal to eat and seizures were the most frequent symptoms. The cohort's mortality was 50% (18/36), while 81.2% (13/18) of survivors displayed cognitive impairment. DISCUSSION: Mexico needs a comprehensive treatment protocol for the care of MSUD patients including newborn screening, early treatment, follow-up and genetic counseling.

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Background. The use of combinations of antibiotics has been the cornerstone of therapy for febrile patients with cancer and severe neutropenia. Each empirical regimen should be selected according to the epidemiology and susceptibility patterns in each center. We describe here the experience wtih empirical antimicrobiial treatments in pediatric patients with cancer, fever and severe neutropenia, and identify the risk factors associated with treatment failure. Methods. This is a prospective study including 145 patients with cancer, and 171 episodes of neutropenia and fever. Blood cultures were taken before initiating empirical treatment: a)carbenicillin (400 mg/kg/day) plus amikacin (21 mg/kg/day) (Cb/ak), and b) ceftazidime (100 mg/kg/day), plus amikacin at the same dosage (Cz/ak). Results. The overall response rate was 54.9 percent and 56.3 percent for Cb/ak and Cz/ak, respectively. Fifty-seven episodes (33.3 percent) were microbiologically documented, gram-positive isolated in 38 percent and gram-negative in 49 percent. Risk factors associated significantly with treatment failure were acute mywlocytic leukemia (AML) (RR 2.59, CI 95 percent 1.42-4.7, p=0.003); bacteriological identification (RR= 4.41, CI 95 percent 2.21 - 8.8, p<0.001), and the presence of two or more sites of infection (RR= 2.89, CI 95 percent 1.03 - 8.11, p=0.03). Conclusions. The rates of response are similar to the combinations used in the hospital (Cb/ak, Cz/ak). The risk factors associated with treatment failure were AML diagnosis, bacteriological identification, and the presence of two or more sites of infection

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