Controles de calidad externos en el diagnóstico molecular de enfermedades genéticas. Impacto sobre la calidad de los estudios genéticos / External quality controls in the molecular diagnosis of genetic diseases. Impact on the quality of the genetic studies / Controles de qualidade externos no diagnóstico molecular de doenças genéticas. Impacto na qualidade dos estudos genéticos

Resumen La participación en programas de evaluación externa de la calidad (PEEC) dirigidos al diagnóstico de enfermedades genéticas permite obtener una medida objetiva del desempeño técnico y analítico de los laboratorios y es un requisito para la acreditación de los laboratorios clínicos bajo la norma ISO 15189. El objetivo de este estudio fue evaluar retrospectivamente el desempeño en los esquemas EMQN (European Molecular Genetics Quality Network) y CF Network (Cystic Fibrosis European Network) en el período 2014-2022. Se participó en un total de 88 esquemas. Se recolectó la información de nuestros puntajes y las medias de los laboratorios participantes en las categorías genotipificación, interpretación y exactitud de la información del paciente/informe. Se informó en forma completa el 90,9% (n=80) de los esquemas. El desempeño en genotipificación mostró puntajes superiores a la media en el 89,3% de los esquemas; 0,8% de los informes correspondieron a falsos negativos. En interpretación, el 66,7% de los esquemas evidenció un desempeño superior a la media y el 33,3% debajo de la media. La exactitud de la información del paciente/informe presentó puntajes superiores a la media en el 97,6% de los esquemas. Se observó una diferencia estadísticamente significativa en el porcentaje de esquemas con puntaje por encima de la media en el año 2022 (10/12 esquemas) respecto al año 2014 (1/6 esquemas) en la categoría interpretación (p=0,0128). En conclusión, la participación regular en PEEC tuvo impacto positivo en la calidad de los estudios y permite realizar mejoras continuas a partir de las recomendaciones sugeridas por estos programas.

Abstract Participation in external quality assessment programmes focused on rare genetic diseases makes it possible to assess the laboratory technical and analytical performance and it is a prerequisite for accreditation according to ISO 15189. The objective of this study was to perform a retrospective evaluation of our performance in the EMQN (European Molecular Genetics Quality Network) and the CF Network (Cystic Fibrosis European Network) programmes in the 2014-2022 period. The laboratory performance on genotyping, interpretation and clerical accuracy and patient identifiers in a total of 88 schemes were assessed. The information of our scores and the mean scores of all participating laboratories in the three categories were collected. A total of 90.9% of the schemes were fully completed. The performance in genotyping showed scores above the mean scores in 89.3% of the schemes; 0.8% of the reports correspond to false negative results. Regarding interpretation category, 66.7% of the schemes presented scores above the mean scores and 33.3% below the mean scores. The clerical accuracy and patient identifiers were above the mean scores in 97.6% of the schemes. A statistically significant difference in the percentage of schemes with a score above the mean for the interpretation category in the year 2022 (10/12 schemes) was observed compared to the year 2014 (1/6 schemes) (p=0.0128). In conclusion, regular participation in external quality assessment programmes had a positive impact on the quality of the studies and allows for continuous improvements based on the recommendations suggested by these programmes.

Resumo A participação em programas de avaliação externa da qualidade (PEECs) voltados para o diagnóstico de doenças genéticas permite obter uma mensuração objetiva do desempenho técnico e analítico dos laboratórios e é requisito para a acreditação dos laboratórios clínicos sob a norma ISO 15189. O objetivo desse estudo foi avaliar retrospectivamente o desempenho nos esquemas EMQN (European Molecular Genetics Quality Network) e CF Network (Cystic Fibrosis European Network) no período 2014-2022. Participou-se em um total de 88 esquemas. Foram coletadas informações de nossos escores e das médias dos laboratórios participantes nas categorias genotipagem, interpretação e precisão da informação do paciente/laudo. 90,9% (n=80) dos esquemas foram informados em sua totalidade. O desempenho na genotipagem apresentou escores acima da média em 89,3% dos esquemas; 0,8% dos laudos corresponderam a falsos negativos. Na interpretação, 66,7% dos esquemas apresentaram desempenho acima da média e 33,3% abaixo da média. A precisão das informações do paciente/laudo apresentou escores acima da média em 97,6% dos esquemas. Observou-se diferença estatisticamente significativa no percentual de esquemas com pontuação acima da média no ano de 2022 (10/12 esquemas) em relação ao ano de 2014 (1/6 esquemas) na categoria interpretação (p=0,0128). Em conclusão, a participação regular em PEECs teve um impacto positivo na qualidade dos estudos e permite fazer melhorias contínuas com base nas recomendações sugeridas por esses programas.

Clinical, neuroradiological, and molecular characterization of mitochondrial threonyl-tRNA-synthetase (TARS2)-related disorder.

PURPOSE: Biallelic variants in TARS2, encoding the mitochondrial threonyl-tRNA-synthetase, have been reported in a small group of individuals displaying a neurodevelopmental phenotype but with limited neuroradiological data and insufficient evidence for causality of the variants. METHODS: Exome or genome sequencing was carried out in 15 families. Clinical and neuroradiological evaluation was performed for all affected individuals, including review of 10 previously reported individuals. The pathogenicity of TARS2 variants was evaluated using in vitro assays and a zebrafish model. RESULTS: We report 18 new individuals harboring biallelic TARS2 variants. Phenotypically, these individuals show developmental delay/intellectual disability, regression, cerebellar and cerebral atrophy, basal ganglia signal alterations, hypotonia, cerebellar signs, and increased blood lactate. In vitro studies showed that variants within the TARS2301-381 region had decreased binding to Rag GTPases, likely impairing mTORC1 activity. The zebrafish model recapitulated key features of the human phenotype and unraveled dysregulation of downstream targets of mTORC1 signaling. Functional testing of the variants confirmed the pathogenicity in a zebrafish model. CONCLUSION: We define the clinico-radiological spectrum of TARS2-related mitochondrial disease, unveil the likely involvement of the mTORC1 signaling pathway as a distinct molecular mechanism, and establish a TARS2 zebrafish model as an important tool to study variant pathogenicity.

Clinical and molecular characterization of mitochondrial DNA disorders in a group of Argentinian pediatric patients.

OBJECTIVE: To describe the clinical and molecular features of a group of Argentinian pediatric patients with mitochondrial DNA (mtDNA) disorders, and to evaluate the results of the implementation of a classical approach for the molecular diagnosis of mitochondrial diseases. METHODS: Clinical data from 27 patients with confirmed mtDNA pathogenic variants were obtained from a database of 89 patients with suspected mitochondrial disease, registered from 2014 to 2020. Clinical data, biochemical analysis, neuroimaging findings, muscle biopsy and molecular studies were analyzed. RESULTS: Patients were 18 females and 9 males, with ages at onset ranging from 1 week to 14 years (median = 4 years). The clinical phenotypes were: mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome (n = 11), Leigh syndrome (n = 5), Kearns-Sayre syndrome (n = 3), Chronic Progressive External Ophthalmoplegia (n = 2), Leber hereditary optic neuropathy (n = 2), myoclonic epilepsy associated with ragged-red fibers (n = 1) and reversible infantile myopathy with cytochrome-C oxidase deficiency (n = 3). Most of the patients harbored pathogenic single nucleotide variants, mainly involving mt-tRNA genes, such as MT-TL1, MT-TE and MT-TK. Other point variants were found in complex I subunits, like MT-ND6, MT-ND4, MT-ND5; or in MT-ATP6. The m.13513G > A variant in MT-ND5 and the m.9185 T > C variant in MT-ATP6 were apparently de novo. The rest of the patients presented large scale-rearrangements, either the "common" deletion or a larger deletion. CONCLUSIONS: This study highlights the clinical and genetic heterogeneity of pediatric mtDNA disorders. All the cases presented with classical phenotypes, being MELAS the most frequent. Applying classical molecular methods, it was possible to achieve a genetic diagnosis in 30% of the cases, suggesting that this is an effective first approach, especially for those centers from low-middle income countries, leaving NGS studies for those patients with inconclusive results.

Molecular diagnosis of epileptic encephalopathy of the first year of life applying a customized gene panel in a group of Argentinean patients.

OBJECTIVE: The aim of this study was to perform a molecular characterization of 17 Argentinean pediatric patients with diagnosis of having epileptic encephalopathies (EEs) of the first year of life without known etiology, applying next-generation sequencing (NGS). METHODS: We included 17 patients with EE with age of onset under 12 months without known etiology after ruling out structural abnormalities, metabolic disorders, and large chromosomal abnormalities. They presented with the following clinical phenotypes: Dravet syndrome (DS; n: 7), epilepsy of infancy with migrating focal seizures (EIMFS; n: 3), West syndrome (WS; n: 2), and undetermined epileptic encephalopathy (UEE; n: 5). Neurologic examinations, seizure semiology, brain magnetic resonance imaging, and standard electroencephalography (EEG) or video-EEG studies were performed in all cases. Using a custom amplicon strategy, we designed an NGS panel to study 47 genes associated with EEs. RESULTS: Pathogenic variants were detected in 8 cases (47%), including seven novel pathogenic variants and one previously reported as being pathogenic. The pathogenic variants were identified in 6 patients with DS (SCN1A gene), one with EIMFS (SCN2A gene), and one with UEE (SLC2A1 gene). Nonrelevant variants were identified in the patients with WS. CONCLUSION: We demonstrated the feasibility of an NGS-gene panel approach for the analysis of patients with EE in our setting. A genetic diagnosis was achieved in nearly 50% of patients, 87% of them presenting with nonpreviously reported variants. The early identification of the underlying causative genetic alteration will be a valuable tool for providing prognostic information and genetic counselling and also to improve therapeutic decisions in Argentinean patients.

Genotype-phenotype correlation of SMN locus genes in spinal muscular atrophy children from Argentina.

BACKGROUND/PURPOSE: Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder, considered one of the leading causes of infant mortality. It is caused by mutations in the SMN1 gene. A highly homologous copy of this gene named SMN2 and other neighbouring genes, SERF1A and NAIP, are considered phenotypic modifiers of the disease. In recent years, notable advances have been made in SMA research regarding evaluation, prognosis, and therapeutic options. Thus, genotype-phenotype studies in SMA are important to stratify patients for motor function tests and for envisaged clinical trials. The aim of this study was to provide clinical and molecular data of a series of Argentinean children with SMA to establish a comprehensive genotype-phenotype correlation. METHODS: 144 Argentinean children with SMA (56 children with type I, 58 with type II, and 30 with type III) were evaluated. The copy number of SMN2, SERF1A, and NAIP genes was established using MLPA (Multiplex Ligation-dependent Probe Amplification) and then correlated with the patients clinical subtypes. To improve clinical characterization we considered the initial symptoms that prompted the consultation, age of acquisition of motor abilities to independent walking and age at loss of gait. We also evaluated clinical and molecular features of sibling pairs in seven families. RESULTS: A strong correlation was observed between the SMN2 copy number and SMA phenotype while SERF1A and NAIP copy number showed a moderate correlation. We observed intra- and inter-family differences among the SMA types. CONCLUSION: This first genotype-phenotype correlation study in Argentinean SMA children provides data to improve patient stratification and define more adequate follow-up parameters.

Pharmacogenetic studies in children with acute lymphoblastic leukemia in Argentina.

The aim of this study was to evaluate the influence of the most common genetic variants in methylenetetrahydrofolate reductase (MTHFR), thiopurine methyltransferase (TPMT) and glutathione-S-transferases (GSTs) on the outcome of acute lymphoblastic leukemia (ALL) treatment in Argentinean children. Two hundred and eighty-six patients with ALL treated with two Berlin-Frankfurt-Münster (BFM)-based protocols were analyzed. Ten genetic variants were studied. Toxicity was evaluated during the consolidation phase. Children who received 2 g/m(2)/day of methotrexate and carried at least one 677T allele in MTHFR showed an increased risk of developing severe leukopenia (p = 0.004) and neutropenia (p = 0.003). Intermediate-risk (IR) patients with a heterozygous TPMT genotype had a higher probability of event-free survival than those with a wild-type genotype. Genotyping of MTHFR polymorphisms might be useful to optimize consolidation therapy, reducing the associated severe hematologic toxicity. Further studies are necessary to establish the usefulness of MTHFR and TPMT variants as additional markers to predict outcome in the IR group.