Brain function in classic galactosemia, a galactosemia network (GalNet) members review.

Classic galactosemia (CG, OMIM #230400, ORPHA: 79,239) is a hereditary disorder of galactose metabolism that, despite treatment with galactose restriction, affects brain function in 85% of the patients. Problems with cognitive function, neuropsychological/social emotional difficulties, neurological symptoms, and abnormalities in neuroimaging and electrophysiological assessments are frequently reported in this group of patients, with an enormous individual variability. In this review, we describe the role of impaired galactose metabolism on brain dysfunction based on state of the art knowledge. Several proposed disease mechanisms are discussed, as well as the time of damage and potential treatment options. Furthermore, we combine data from longitudinal, cross-sectional and retrospective studies with the observations of specialist teams treating this disease to depict the brain disease course over time. Based on current data and insights, the majority of patients do not exhibit cognitive decline. A subset of patients, often with early onset cerebral and cerebellar volume loss, can nevertheless experience neurological worsening. While a large number of patients with CG suffer from anxiety and depression, the increased complaints about memory loss, anxiety and depression at an older age are likely multifactorial in origin.

Body composition in patients with hepatic glycogen storage diseases.

OBJECTIVES: The present study aimed to evaluate the body composition of hepatic glycogen storage disorders (GSDs) through dual energy x-ray absorptiometry. METHODS: This was an exploratory, observational, cross-sectional study. Twenty-four patients with GSD (type Ia: n = 13, Ib: n = 5, III: n = 2, and IX-α/ß/γ: n = 4; female sex: n = 13; age <8 y: n = 3, 8-19 y: n = 14, and >19 y: n = 7) were included. Three-day dietary records were collected in the week preceding dual energy x-ray absorptiometry. Body composition findings were correlated with clinical parameters, uncooked cornstarch (UCCS) regimen, dietary intake, and markers of treatment adherence. RESULTS: An elevated fat mass (FM) index was found in 16 of 21 patients (age 8-19 y: n = 10 and >19 y: n = 6; GSD type Ia: n = 12, Ib: n = 2, III: n = 1, and IX-γ: n = 1). A lean mass (LM) index evaluation showed no LM deficits in relation to corresponding reference populations. Relative skeletal muscle index values were decreased in 2 of 7 adult patients (type Ib: n = 1 and IX-α: n = 1). UCCS (g/d) correlated positively with the FM index (rs = 0.7; P ≤ 0.01). In contrast, relative UCCS intake (g/kg body weight) was negatively associated with LM/kg (rs = -0.8; P ≤ 0.01). CONCLUSIONS: These findings suggest a high frequency of elevated FM in patients with hepatic GSDs. We also suggest that treatment with UCCS is associated with excess weight in these patients. Additionally, the treatment strategy can impair protein intake, and lead to a decrease in LM.

Epidemiology of rare diseases in Brazil: protocol of the Brazilian Rare Diseases Network (RARAS-BRDN).

The Brazilian Policy of Comprehensive Care for People with Rare Diseases (BPCCPRD) was established by the Ministry of Health to reduce morbidity and mortality and improve the quality of life of people with rare diseases (RD). Several laboratory tests, most using molecular genetic technologies, have been incorporated by the Brazilian Public Health System, and 18 specialised centres have so far been established at university hospitals (UH) in the capitals of the Southern, Southeastern and Northeastern regions. However, whether the available human and technological resources in these services are appropriate and sufficient to achieve the goals of care established by the BPCCPRD is unknown. Despite great advances in diagnosis, especially due to new technologies and the recent structuring of clinical assessment of RD in Brazil, epidemiological data are lacking and when available, restricted to specific disorders. This position paper summarises the performance of a nationally representative survey on epidemiology, clinical status, and diagnostic and therapeutic resources employed for individuals with genetic and non-genetic RD in Brazil. The Brazilian Rare Disease Network (BRDN) is under development, comprising 40 institutions, including 18 UH, 17 Rare Diseases Reference Services and five Newborn Screening Reference Services. A retrospective study will be initially conducted, followed by a prospective study. The data collection instrument will use a standard protocol with sociodemographic data and clinical and diagnostic aspects according to international ontology. This great collaborative network is the first initiative of a large epidemiological data collection of RD in Latin America, and the results will increase the knowledge of RD in Brazil and help health managers to improve national public policy on RD in Brazil.

Brazilian Food Reference Guide for Phenylalanine Content: A Study Based on the Perception of PKU Patients and Health Providers

Abstract The mainstay of management of phenylketonuria (PKU) is restriction of dietary phenylalanine (Phe) intake. The present study sought to assess the perception and understanding of health care providers and lay users (patients/family members/caregivers) regarding the national reference database for checking the Phe content of foods, provided by the Brazilian Health Regulatory Agency (Anvisa), whose data are presented in the Table of Phenylalanine Content of Foods (TCFA-Anvisa) and recently in the Phenylalanine Content of Foods Dashboard (PCCFA-Anvisa); and to identify factors which interfere with the usability of these resources. Two online questionnaires, one for providers (n=33) and another for lay users (n=194), were used to collect sociodemographic information, knowledge about dietary management of PKU, sources of information about the Phe content of foods, and perception and understanding of the Anvisa tools. TCFA-Anvisa and PCCFA-Anvisa were not used as main sources of information by either group. Among the participants who had used these tools (15 providers;35 lay users), most considered the PCCFA-Anvisa to be superior or partially superior to the TCFA-Anvisa. The main limitations reported were related to layout and limited variety of foods. We suggest that the limitations identified in this study be considered for future improvement of these resources.

Adenosine kinase deficiency presenting with tortuous cervical arteries: A risk factor for recurrent stroke.

Adenosine kinase (ADK) deficiency is a very rare inborn error of methionine and adenosine metabolism. It is characterized by developmental delay, hypotonia, epilepsy, facial dysmorphism, failure to thrive, transient liver dysfunction with cholestasis, recurrent hypoglycemia, and cardiac defects. Only 26 cases (16 families) of ADK deficiency have been published since its identification in 2011. Vascular abnormalities in cervical arteries and cerebral stroke have never been reported in this condition. Here, we describe two patients with ADK deficiency and vascular tortuosity leading to stroke in one of them. ADK deficiency is a rare inborn error of methionine metabolism with a complex phenotype that might be associated with cerebrovascular abnormalities and stroke.

Epidemiological aspects of hereditary fructose intolerance: A database study.

Hereditary fructose intolerance (HFI) is an inborn error of fructose metabolism of autosomal recessive inheritance caused by pathogenic variants in the ALDOB gene that lead to aldolase B deficiency in the liver, kidneys, and intestine. Patients manifest symptoms, such as ketotic hypoglycemia, vomiting, nausea, in addition to hepatomegaly and other liver and kidney dysfunctions. The treatment consists of a fructose-restricted diet, which results in a good prognosis. To analyze the distribution of ALDOB variants described in patients and to estimate the prevalence of HFI based on carrier frequency in the gnomAD database, a systematic review was conducted to assess ALDOB gene variants among patients with HFI. The prevalence of HFI was estimated from the carrier frequency of variants described in patients, as well as rare variants predicted as pathogenic by in silico tools. The p.(Ala150Pro) and p.(Ala175Asp) variants are the most frequent and are distributed worldwide. However, these variants have particular distribution patterns in Europe. The analysis of the prevalence of HFI showed that the inclusion of rare alleles predicted as pathogenic is a more informative approach for populations with few patients. The data show that HFI has a wide distribution and an estimated prevalence of ~1:10,000.

Impact of the COVID-19 pandemic on the standard of care for patients with lysosomal storage diseases: A survey of healthcare professionals in the Fabry, Gaucher, and Hunter Outcome Survey registries.

The impact of the COVID-19 pandemic on the standards of care of patients with lysosomal storage diseases and the needs of their healthcare providers were explored using a 12-question survey. Overall, 80/91 respondents (88%) indicated that the pandemic had negatively affected standards of care. With increased reliance on telemedicine, the respondents highlighted the need for a personalized approach to care, direct and frequent communication with patients, and greater involvement of patients and caregivers.

Pathogenic variants in GNPTAB and GNPTG encoding distinct subunits of GlcNAc-1-phosphotransferase differentially impact bone resorption in patients with mucolipidosis type II and III.

PURPOSE: Pathogenic variants in GNPTAB and GNPTG, encoding different subunits of GlcNAc-1-phosphotransferase, cause mucolipidosis (ML) II, MLIII alpha/beta, and MLIII gamma. This study aimed to investigate the cellular and molecular bases underlying skeletal abnormalities in patients with MLII and MLIII. METHODS: We analyzed bone biopsies from patients with MLIII alpha/beta or MLIII gamma by undecalcified histology and histomorphometry. The skeletal status of Gnptgko and Gnptab-deficient mice was determined and complemented by biochemical analysis of primary Gnptgko bone cells. The clinical relevance of the mouse data was underscored by systematic urinary collagen crosslinks quantification in patients with MLII, MLIII alpha/beta, and MLIII gamma. RESULTS: The analysis of iliac crest biopsies revealed that bone remodeling is impaired in patients with GNPTAB-associated MLIII alpha/beta but not with GNPTG-associated MLIII gamma. Opposed to Gnptab-deficient mice, skeletal remodeling is not affected in Gnptgko mice. Most importantly, patients with variants in GNPTAB but not in GNPTG exhibited increased bone resorption. CONCLUSION: The gene-specific impact on bone remodeling in human individuals and in mice proposes distinct molecular functions of the GlcNAc-1-phosphotransferase subunits in bone cells. We therefore appeal for the necessity to classify MLIII based on genetic in addition to clinical criteria to ensure appropriate therapy.

Hipoventilação relacionada ao sono de origem central secundária à deficiência de biotinidase: relato de caso / Sleep-related hypoventilation due to partial biotinidase deficiency: a case repor

RESUMO: A hipoventilação relacionada ao sono de origem central resulta em hipercapnia relacionada ao sono na vigência de condições normais do sistema respiratório e excluindo-se outros fatores. Os pacientes portadores dessa patologia podem se apresentar assintomáticos ou com queixas de cefaleia matinal, déficit cognitivo e fadiga, além de eventos como a observação de respiração superficial. No presente relato, descreve-se o caso de uma paciente de três anos, com exame físico geral e neurológico normais, desenvolvimento neuropsicomotor adequado, apresentando irregu-laridades respiratórias e bradicardia durante o sono. Encaminhada para investigação de distúrbios respiratórios do sono, sendo diagnosticada com hipoventilação relacionada ao sono. Através do estudo genético, evidenciou-se a deficiência de biotinidase como a possível causa da sintomatologia, comprovada por dosagens enzimáticas e teste genético molecular. O tratamento medicamentoso foi iniciado precocemente, determinando resolução dos sintomas descritos. A importância do presente relato se encontra na apresentação da deficiência da biotinidase com quadro cardiorrespiratório isolado em criança neurologicamente normal, ademais trata-se de um caso em que a etiologia de Breath-Holding Spells foi a deficiência dessa enzima. Correspondência sugerida pela resolução da hipoventila-ção central após a introdução da biotina. Além disso, nesse caso, os sintomas Apparent Life-Threatening Events, que aterrorizam o observador e até o profissional, foram solucionados com tratamento simples, a ingesta oral de biotina. Esse relato de caso corrobora com a expansão das possibilidades de manifestações fenotípicas das formas tardias de deficiência de biotinidase, como o fenótipo da Síndrome da Hipoventilação Central. (AU)

ABSTRACT: Idiopathic sleep-related hypoventilation occurs in individuals with hypercapnia during sleep in normal conditions of the respiratory system in the absence of other disorders. Patients with this condition may be asymptomatic or have complaints of morning headache, cognitive deficit and fatigue, and observation of shallow breathing. This report describes the case of a 3-year-old patient with normal physical and neurological exam, appropriate neuropsychomotor development, presenting breathing irregularities, and bradycardia during sleep. The patient was referred to an investigation for sleep respiratory disturbs and was diagnosed with hypoventilation related to sleep. The genetic study, done by enzymatic dosages and molecular genetic tests, showed the deficiency of biotinidase as a possible cause of symptomatology. The drug treatment was initiated early with the resolution of the symptoms. The present clinical report highlights the biotinidase deficiency with an isolated cardiorespiratory condition in a neurologically normal child, which also led to Breath-Holding Spells. This relation was suggested after central hypoventilation resolution following biotin introduction. Besides, Apparent Life-Threatening Events symptoms, which terrify the observer and even professionals, disappeared after the oral intake of biotin. Finally, this case report corroborates the expansion of possibilities for the phenotypic manifestations of late cases from biotinidase deficiency, as the SHC phenotyp. ((AU)

A triple-blinded crossover study to evaluate the short-term safety of sweet manioc starch for the treatment of glycogen storage disease type Ia.

BACKGROUND: Glycogen storage disease type 1a (GSD Ia) is characterized by severe fasting hypoglycemia. The clinical management includes the administration of uncooked cornstarch (UCCS). Although such a diet approach is effective in achieving euglycemia, its impact on the quality of life of patients should be considered. In vitro analyses suggest a longer release of glucose when using sweet manioc starch (SMS). METHODS: We compared the efficacy and safety of the administration of SMS and UCCS during a short-fasting challenge in patients with GSD Ia in a randomized, triple-blind, phase I/II, cross-over study. GSD Ia patients aged ≥ 16 years and treated with UCCS were enrolled. Participants were hospitalized for two consecutive nights, receiving UCCS or SMS in each night. After the administration of the starches, glucose, lactate and insulin levels were measured in 1-h interval throughout the hospitalization period. The procedures were interrupted after 10 h of fasting or in a hypoglycemic episode (< 3.88 mmol/L). RESULTS: Eleven individuals (mean age: 21.6 ± 4.3 years; all presenting body mass index > 25 kg/m2) participated in the study. The average fasting period was 8.2 ± 2.0 h for SMS and 7.7 ± 2.3 h for UCCS (p = 0.04). SMS maintained euglycemia for a greater period over UCCS. Increased lactate concentrations were detected even in absence of hypoglycemia, not being influenced by the different starches investigated (p = 0.17). No significant difference was found in total cholesterol, HDL, triglycerides and uric acid levels in both arms. None of the patients showed severe adverse events. CONCLUSIONS: SMS appears to be non-inferior to UCCS in the maintenance of euglycemia, thus emerging as a promising alternative to the treatment of GSD Ia.

Gender, Race and Parenthood Impact Academic Productivity During the COVID-19 Pandemic: From Survey to Action.

The coronavirus disease 2019 (COVID-19) pandemic is altering dynamics in academia, and people juggling remote work and domestic demands - including childcare - have felt impacts on their productivity. Female authors have faced a decrease in paper submission rates since the beginning of the pandemic period. The reasons for this decline in women's productivity need to be further investigated. Here, we analyzed the influence of gender, parenthood and race on academic productivity during the pandemic period based on a survey answered by 3,345 Brazilian academics from various knowledge areas and research institutions. Productivity was assessed by the ability to submit papers as planned and to meet deadlines during the initial period of social isolation in Brazil. The findings revealed that male academics - especially those without children - are the least affected group, whereas Black women and mothers are the most impacted groups. These impacts are likely a consequence of the well-known unequal division of domestic labor between men and women, which has been exacerbated during the pandemic. Additionally, our results highlight that racism strongly persists in academia, especially against Black women. The pandemic will have long-term effects on the career progression of the most affected groups. The results presented here are crucial for the development of actions and policies that aim to avoid further deepening the gender gap in academia.

A decade of molecular diagnosis of Mucolipidosis II and III in Brazil: a pooled analysis of 32 patients

Abstract GlcNAc-1-phosphotransferase is a hexameric complex formed by subunits α, β, and γ, where the first two are encoded by the GNPTAB gene and the third by the GNPTG gene. Pathogenic variants identified in the GNPTAB gene cause the diseases Mucolipidosis II and III alpha/beta, which are severe and characterized by an overflow of lysosomal hydrolases into the extracellular environment, and their absence in lysosomal compartments causes an accumulation of non-degraded macromolecules. Methodology: a retrospective study that included 32 unrelated Brazilian patients with a clinical and genetic diagnosis of Mucolipidosis II/III alpha/beta. The regional frequency of the altered alleles was determined. Results: The patients were from all regions of Brazil. The most prevalent variants were c.3503_3504del, associated with the severe form of the disease, and c.1208T>C, associated with the milder form. Variant c.3503_3504del is the most frequently found in the Midwest, Northeast, and Southeast regions of Brazil. In the South, 42.8% of the alleles present the c.1196C>T variant. Conclusions: From the perspective of all patients diagnosed with Mucolipidosis II/III in Brazil, it is possible to conclude that different regions present allelic frequencies of specific pathogenic variants, which can be explained by the occurrence of a founding effect or high inbreeding rates.

Imbalanced cellular metabolism compromises cartilage homeostasis and joint function in a mouse model of mucolipidosis type III gamma.

Mucolipidosis type III (MLIII) gamma is a rare inherited lysosomal storage disorder caused by mutations in GNPTG encoding the γ-subunit of GlcNAc-1-phosphotransferase, the key enzyme ensuring proper intracellular location of multiple lysosomal enzymes. Patients with MLIII gamma typically present with osteoarthritis and joint stiffness, suggesting cartilage involvement. Using Gnptg knockout (Gnptgko ) mice as a model of the human disease, we showed that missorting of a number of lysosomal enzymes is associated with intracellular accumulation of chondroitin sulfate in Gnptgko chondrocytes and their impaired differentiation, as well as with altered microstructure of the cartilage extracellular matrix (ECM). We also demonstrated distinct functional and structural properties of the Achilles tendons isolated from Gnptgko and Gnptab knock-in (Gnptabki ) mice, the latter displaying a more severe phenotype resembling mucolipidosis type II (MLII) in humans. Together with comparative analyses of joint mobility in MLII and MLIII patients, these findings provide a basis for better understanding of the molecular reasons leading to joint pathology in these patients. Our data suggest that lack of GlcNAc-1-phosphotransferase activity due to defects in the γ-subunit causes structural changes within the ECM of connective and mechanosensitive tissues, such as cartilage and tendon, and eventually results in functional joint abnormalities typically observed in MLIII gamma patients. This idea was supported by a deficit of the limb motor function in Gnptgko mice challenged on a rotarod under fatigue-associated conditions, suggesting that the impaired motor performance of Gnptgko mice was caused by fatigue and/or pain at the joint.This article has an associated First Person interview with the first author of the paper.

Prevalence of the most common pathogenic variants in three genes for inborn errors of metabolism associated with sudden unexpected death in infancy: a population-based study in south Brazil.

Citrullinemia type 1 (CTLNI), long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD), and mut0 methylmalonic acidemia (mut0 MMA) are inborn errors of metabolism (IEMs) associated with sudden unexpected death in infancy (SUDI). Its most common pathogenic variants are: c.1168G>A (CTLNI, ASS1 gene), c.1528G>C (LCHADD, HADHA gene), c.655A>T and c.1106G>A (mut0 MMA, MUT gene). Considering the absence of estimates regarding the incidence of these diseases in Brazil, this study sought to investigate the prevalence of its main pathogenic variants in a healthy population in the southern region of the country. A total of 1,000 healthy subjects from Rio Grande do Sul were included. Genotyping was performed by real-time PCR. Individuals found to be heterozygous for c.1528G>C underwent further acylcarnitine profile analysis by tandem mass spectrophotometry. Allele and genotype frequencies were calculated considering Hardy-Weinberg equilibrium. The c.1528G>C variant was detected in heterozygosity in two subjects (carrier frequency = 1:500; allele frequency = 0.001; minimum prevalence of LCHADD = 1: 1,000,000), whose acylcarnitine profiles were normal. Variants c.1168G>A, c.655A>T, and c.1106G>A were not identified. These results denote the rarity of these IEMs in Southern Brazil, highlighting the need to expand the investigation of IEMs in relation to infant morbidity and mortality within the country.

Classical homocystinuria: A common inborn error of metabolism? An epidemiological study based on genetic databases.

BACKGROUND: Biallelic pathogenic variants in CBS gene cause the most common form of homocystinuria, the classical homocystinuria (HCU). The worldwide prevalence of HCU is estimated to be 0.82:100,000 [95% CI, 0.39-1.73:100,000] according to clinical records and 1.09:100,000 [95% CI, 0.34-3.55:100,000] by neonatal screening. In this study, we aimed to estimate the minimal worldwide incidence of HCU. METHODS: The 25 most common pathogenic alleles of HCU were identified through a literature review. The incidence of HCU was estimated based on the frequency of these common pathogenic alleles in a large genomic database (gnomAD). RESULTS: The minimum worldwide incidence of HCU was estimated to be ~0.38:100,000, and the incidence was higher in Europeans non-Finnish (~0.72:100,000) and Latin Americans (~0.45:100,000) and lower in Africans (~0.20:100,000) and Asians (~0.02:100,000). CONCLUSION: Our data are in accordance with the only published metanalysis on this topic. To our surprise, the observed incidence of HCU in Europeans was much lower than those described in articles exploring small populations from northern Europe but was similar to the incidence described on the basis of neonatal screening programs. In our opinion, this large dataset analyzed and its population coverage gave us greater precision in the estimation of incidence.

Prevalence and causes of congenital microcephaly in the absence of a Zika virus outbreak in southern Brazil / Prevalência e causas da microcefalia congênita sem a presença do surto do vírus Zika no Sul do Brasil

Abstract Objective: The aim of this study was to identify the causes of congenital microcephaly in Rio Grande do Sul, a state in southern Brazil, where no ZIKV outbreak was detected, from December 2015 to December 2016, which was the period when ZIKV infection was at its peak in northeast Brazil. Methods: This was a cross-sectional study where all notifications of congenital microcephaly in the state of Rio Grande do Sul were included for analysis. Evaluation of cases followed the guidelines of the Brazilian Ministry of Health. Dysmorphological and neurological evaluations were performed by a specialized team, and genetic tests and neuroimaging were performed when clinically indicated. STORCH infections were diagnosed using standard tests. ZIKV infection was diagnosed through maternal serum RT-PCR and/or neuroimaging associated with clinical/epidemiological criteria. Results: From 153 744 registered live births in the study period, 148 cases were notified, but 90 (60.8%) of those were later excluded as "non-confirmed" microcephaly. In the 58 confirmed cases of microcephaly (prevalence = 3.8/10 000 live births), congenital infections (syphilis, toxoplasmosis, cytomegalovirus, and ZIKV) constituted the predominant etiology (50.0%), followed by isolated CNS (15.5%), and genetic syndromes (10.3%). Congenital ZIKV syndrome (CZS) with typical phenotype was diagnosed in three cases (5.2% of all confirmed microcephaly cases or 10.4% of all congenital infections). Conclusion: In Rio Grande do Sul, where no outbreak of ZIKV infection was recorded, congenital infections were the leading cause of congenital microcephaly, and the attributable risk for CZS in the etiology of microcephaly was 5.2%.

Resumo: Objetivo: Identificar as causas da microcefalia congênita no Rio Grande do Sul, Região Sul do Brasil, onde não foi detectado surto de ZIKV, de dezembro de 2015 a dezembro de 2016. Esse foi o período em que a infecção por ZIKV estava em seu auge no Nordeste do Brasil. Métodos: Este é um estudo transversal no qual todas as notificações de microcefalia congênita no estado do Rio Grande do Sul foram incluídas para análise. A avaliação dos casos seguiu as orientações do Ministério da Saúde. A avaliação dismorfológica e neurológica foi feita por uma equipe especializada e os testes genéticos e as neuroimagens foram feitos quando indicado clinicamente. As infecções STORCH (Sífilis, Toxoplasmose, Rubéola, Citomegalovírus e Herpes simples) foram diagnosticadas utilizando testes padrão. A infecção por ZIKV foi diagnosticada por meio da transcriptase reversa seguida de reação em cadeia da polimerase (RT-PCR) no soro materno e/ou neuroimagem associada a critérios clínicos/epidemiológicos. Resultados: De 153.744 nascidos vivos registrados no período do estudo, 148 bebês foram casos notificados, porém 90 (60,8%) casos foram excluídos posteriormente como microcefalia "não confirmada". Nos 58 casos confirmados de microcefalia (prevalência = 3,8/10.000 nascidos vivos), as infecções congênitas (sífilis, toxoplasmose, citomegalovírus e ZIKV) constituíram a etiologia predominante (50,0%), seguidas de doenças ligadas ao SNC isolado (15,5%) e síndromes genéticas (10,3%). A síndrome congênita do ZIKV (SCZ) com fenótipo típico foi diagnosticada em três casos (5,2% de todos os casos confirmados de microcefalia ou 10,4% de todas as infecções congênitas). Conclusão: No Rio Grande do Sul, Brasil, onde não foi registrado surto de infecção por ZIKV, a principal causa de microcefalia congênita foram infecções congênitas e o risco atribuível para SCZ na etiologia de microcefalia foi de 5,2%.

Effect of BTD gene variants on in vitro biotinidase activity.

INTRODUCTION: Biotinidase deficiency (BD), an autosomal recessive disease, is classified into profound (activity <10%) or partial BD (activity 10-30%). The most frequent variant in patients worldwide is c.1330G > C (p.Asp444His), which is associated with partial BD. In vivo studies indicate that this variant reduces the biotinidase activity by 50%. The objective of this study was to evaluate the in vitro effect of p.Asp444His and of five novel variants identified among Brazilian individuals showing low activity of biotinidase in serum. METHODS: The variants c.119 T > C (p.Leu40Pro), c.479G > A (p.Cys160Tyr), c.664G > A (p.Asp222Asn), c.1330G > C (p.Asp444His), c.1337 T > C (p.Leu446Pro), c.1466A > G (p.Asn489Ser) and the wild type (wt) BTD gene were expressed in HEK 293 cells. Biotinidase activity was quantified by colorimetric method in cells homogenates and culture medium. The wtBTD activity was considered 100%. RESULTS: The p.Leu40Pro, p.Cys160Tyr and p.Leu446Pro variants were associated to impaired biotinidase activity (activity in cells: 33%, 14%, 0%, respectively; activity in medium: 7%, 0.3%, 2%, respectively) and undetectable amount of protein in intra and extracellular space. The p.Asn489Ser variant had these effects restricted to the extracellular space (activity in medium: 43%), and the p.Asp222Asn variant showed normal activity. The expression of p.Asp444His variant resulted in detectable protein and slightly reduced activity only in cells (activity in cells: 46%; activity in medium: 115%). CONCLUSION: Our findings suggest that the p.Leu40Pro, p.Cys160Tyr and p.Leu446Pro variants are deleterious; the p.Asn489Ser is probably related to a mild biochemical phenotype; and p.Asp222Asn variant is probably not deleterious. The p.Asp444His variant seems to code for a protein with variable activity.