The Chaperones Involved in Hemoglobin Synthesis Take the Spotlight: Analysis of AHSP in the Argentinean Population and Review of the Literature.

Hemoglobin (Hb) synthesis is a complex, well-coordinated process that requires molecular chaperones. These intervene in different steps: regulating epigenetic mechanisms necessary for the adequate expression of the α- and ß-globin clusters, binding the nascent peptides and helping them acquire their native structure, preventing oxidative damage by free globin chains and preventing the cleavage of essential erythroid transcription factors. This study analyzed the distribution of the single nucleotide polymorphism (SNP) rs4296276 in intron 1 of the α-globin chaperone α Hb-stabilizing protein (AHSP) in the Argentinean population. The risk allele was found in thalassemia patients who exhibited more severe phenotypes than expected. Future studies may help establish the role of these chaperones as modifiers in pathological states with globin chain imbalance, such as thalassemia.

Two novel unstable hemoglobin variants due to in-frame deletions of key amino acids in the ß-globin chain.

Hemoglobinopathies are the most common autosomal recessive disorders and are mostly inherited in a recessive manner. However, certain mutations can affect the globin chain stability, leading to dominant forms of thalassemia. The aim of this work was the molecular and structural characterization of two heterozygous in-frame deletions, leading to ß-globin variants in pediatric patients in Argentina. The HBB gene of the probands and their parents was sequenced, and other markers of globin chain imbalance were analyzed. Several structural analyses were performed, and the effect of the mutations on the globin chain stability was analyzed. In Hb JC-Paz, HBB:c.29_37delCTGCCGTTA (p.Ala10_Thr12del), detected in an Argentinean boy, one α-helix turn is expected to be lost. In Hb Tavapy, HBB:c.182_187delTGAAGG (p.Val60_Lys61del), the deleted residues are close to distal histidine (His63) in the heme pocket. Both mutations are predicted to have a destabilizing effect. The development of computational structural models and bioinformatics algorithms is expected to become a useful tool to understand the impact of the mutations leading to dominant thalassemia.

Bases moleculares de hemoglobinopatías en Argentina / Molecular basis of hemoglobinopathies in Argentina / Bases moleculares de hemoglobinopatias na Argentina

Durante el desarrollo de un individuo se expresan distintas cadenas de globina de tipo a y no-a, que se combinan en tetrámeros para formar hemoglobina. Los genes que las codifican se organizan en familias. Distintas mutaciones afectan los genes que codifican las cadenas de globina: si provocan alteraciones cualitativas originan cuadros de hemoglobinopatías estructurales, si disminuyen las síntesis de las cadenas de globina, talasemias, y si tienen ambos efectos, hemoglobinopatías talasémicas. El propósito de este trabajo es presentar las bases moleculares de las hemoglobinopatías en Argentina, en un total de 862 muestras, en base a los estudios moleculares realizados en este laboratorio a partir del estudio de 910 muestras de pacientes. En nuestro medio, la Hb S es la hemoglobinopatía estructural más frecuente, las ß-talasemias presentan una distribución similar a la cuenca del Mediterráneo y las a-talasemias están intrínsecamente relacionadas a la ascendencia de los afectados. Las bases moleculares de las hemoglobinopatías son variadas. Mientras que en las hemoglobinopatías estructurales y ß-talasemias predominan las mutaciones puntuales, en las a-talasemias predominan las deleciones. Se describen mutaciones nóveles (cambios puntuales, deleciones y duplicaciones) que se presentan como eventos aislados con herencia recesiva o dominante. Es necesaria la interacción entre el médico hematólogo, el laboratorio bioquímico, el laboratorio molecular y el médico genetista, para llegar al diagnóstico certero de estos cuadros que permitirán reducir la incidencia de las formas severas.

Functional hemoglobin is a tetramer composed of 2 a and 2 non-a chains, encoded by genes that are organized in clusters and are expressed sequentially through development. There are multiple mutations described that affect these genes: if the sequence variant leads to a qualitative alteration, the resulting effect is a structural hemoglobinopathy, if it decreases the synthesis of the globin chains, thalassemia, and if it affects both the quality and quantity of the globin chain, the consequence is a thalassemic hemoglobinopathy. The aim of this paper is to present the molecular bases of hemoglobinopathies in Argentina, determined in 862 patients, based on the results of the molecular studies carried out in our laboratory from the analysis of 910 samples. Hb S is the most frequent structural hemoglobinopathy, ß-thalassemia mutations exhibit a pattern similar to the one displayed by Mediterranean basin populations, and a-thalassemia mutations are intrinsically related to the ancestry of those affected. These syndromes exhibit diverse molecular bases: structural hemoglobinopathies and ß-thalassemia are a consequence, mostly of point mutations, whereas in a-thalassemia deletions prevail. Novel mutations (point changes, deletions and duplications) that occurred as isolated events, with recessive or dominant inheritance, were described. Interaction between the hematologist, the geneticist and both the clinical and molecular biology laboratories is necessary to reach an accurate diagnosis of these syndromes and reduce the incidence of severe forms.

Durante o desenvolvimento de um indivíduo expressam-se diversas cadeias de globina de tipo a e não-a, que se combinam em tetrámeros para formar hemoglobina. Os genes que as codificam são organizados em famílias. Diferentes mutações afetam os genes que codificam as cadeias de globina: se provocarem alterações qualitativas originam quadros de hemoglobinopatias estruturais, se diminuírem as sínteses das cadeias de globina, talassemias, e se tiverem ambos os efeitos, hemoglobinopatias talassêmicas. O propósito deste trabalho é apresentar as bases moleculares das hemoglobinopatias na Argentina, num total de 862 amostras, com base nos estudos moleculares realizados neste laboratório a partir do estudo de 910 amostras de pacientes. No nosso meio, a Hb S é a hemoglobinopatia estrutural mais frequente, as ß-talassemias apresentam uma distribuição similar à bacia do Mediterrâneo e as a-talassemias estão intrinsecamente relacionadas com a ascendência dos afetados. As bases moleculares das hemoglobinopatias são variadas. Enquanto nas hemoglobinopatias estruturais e ß-talassemias predominam as mutações pontuais, nas a-talassemias predominam as deleções. Descrevem-se mutações incipientes (mudanças pontuais, deleções e duplicações) que se apresentam como eventos isolados com herança recessiva ou dominante. É necessária a interação entre o médico hematólogo, o laboratório bioquímico, o laboratório molecular e o médico geneticista, para chegar ao diagnóstico certo desses quadros que permitirão reduzir a incidência das formas severas.

[Regulation of the ß-globin gene family expression, useful in the search for new therapeutic targets for hemoglobinopathies]. / Regulación de expresión de genes de la familia de ß-globina humana, útil en la búsqueda de nuevos blancos terapéuticos para tratamiento de hemoglobinopatías.

Different hemoglobin isoforms are expressed during the embryonic, fetal and postnatal stages. They are formed by combination of polypeptide chains synthesized from the α- and ß-globin gene clusters. Based on the fact that the presence of high hemoglobin F levels is beneficial in both sickle cell disease and severe thalassemic syndromes, a revision of the regulation of the ß-globin cluster expression is proposed, especially regarding the genes encoding the y-globin chains (HBG1 and HBG2). In this review we describe the current knowledge about transcription factors and epigenetic regulators involved in the switches of the ß-globin cluster. It is expected that the consolidation of knowledge in this field will allow finding new therapeutic targets for the treatment of hemoglobinopathies.

Regulación de expresión de genes de la familia de ß-globina humana, útil en la búsqueda de nuevos blancos terapéuticos para tratamiento de hemoglobinopatías / Regulation of the ß-globin gene family expression, useful in the search for new therapeutic targets for hemoglobinopathies

Durante la etapa embrionaria, el desarrollo fetal y la vida posnatal se expresan isoformas funcionalmente distintas de hemoglobina, producto de la combinación de cadenas polipeptídicas sintetizadas a partir de los distintos genes que componen las familias de α- y β-globina. En función de que la presencia de altos niveles de hemoglobina fetal (Hb F) es beneficiosa en síndromes falciformes y talasémicos graves, se plantea revisar las bases de la regulación de la expresión de los genes de la familia de β-globina, en particular los genes que codifican las cadenas de γ-globina (HBG1 y HBG2). En este trabajo se revisan los conocimientos sobre factores de transcripción y reguladores epigenéticos que gobiernan los eventos de encendido y apagado de los genes de la familia de β-globina. Se espera que la consolidación de estos conocimientos permita hallar nuevos blancos terapéuticos para el tratamiento de hemoglobinopatías.

Different hemoglobin isoforms are expressed during the embryonic, fetal and postnatal stages. They are formed by combination of polypeptide chains synthesized from the α- and β- globin gene clusters. Based on the fact that the presence of high hemoglobin F levels is beneficial in both sickle cell disease and severe thalassemic syndromes, a revision of the regulation of the β-globin cluster expression is proposed, especially regarding the genes encoding the γ-globin chains (HBG1 and HBG2). In this review we describe the current knowledge about transcription factors and epigenetic regulators involved in the switches of the β-globin cluster. It is expected that the consolidation of knowledge in this field will allow finding new therapeutic targets for the treatment of hemoglobinopathies.

Multiple copy number variants in a pediatric patient with Hb H disease and intellectual disability.

Two distinct syndromes that link α-thalassemia and intellectual disability (ID) have been described: ATR-X, due to mutations in the ATRX gene, and ATR-16, a contiguous gene deletion syndrome in the telomeric region of the short arm of chromosome 16. A critical region where the candidate genes for the ID map has been established. In a pediatric patient with Hemoglobin H disease, dysmorphic features and ID, 4 novel and clinically relevant Copy Number Variants were identified. PCR-GAP, MLPA and FISH analyses established the cause of the α-thalassemia. SNP-array analysis revealed the presence of 4 altered loci: 3 deletions (arr[hg19]Chr16(16p13.3; 88,165-1,507,988) x1; arr[hg19]Chr6(6p21.1; 44,798,701-45,334,537) x1 and arr[hg19]Chr17(17q25.3; 80,544,855-81,057,996) x1) and a terminal duplication (arr[hg19]Chr7(7p22.3-p22.2; 4,935-4,139,785) x3). The -α(3.7) mutation and the ∼1.51 Mb in 16p13.3 are involved in the alpha-thalassemic phenotype. However, the critical region for ATR-16 cannot be narrowed down. The deletion affecting 6p21.1 removes the first 2 exons and part of intron 2 of the RUNX2 gene. Although heterozygous loss of function mutations affecting this gene have been associated with cleidocranial dysplasia, the patient does not exhibit pathognomonic signs of this syndrome, possibly due to the fact that the isoform d of the transcription factor remains unaffected. This work highlights the importance of searching for cryptic deletions in patients with ID and reiterates the need of the molecular analysis when it is associated to microcytic hypochromic anemia with normal iron status.

[Molecular bases of α-thalassemia in Argentina]. / Bases moleculares de alfa-talasemia en la Argentina.

The α-thalassemia is one of the most common hereditary disorders worldwide. Currently, molecular diagnostics is the only available tool to achieve an accurate diagnosis. The purpose of this study was to characterize the molecular bases of these syndromes in our environment and to establish genotype-phenotype associations. Through a combination of different molecular techniques and fluorescent in situ hybridization (FISH),we were able to find α-thalassemic mutations in 145 of the 184 patients (78.8%) studied with hematological parameters compatible with α-thalassemia. Deletions of the α-globin genes resulted the major molecular cause of the disease, and the most frequent mutation was -α(3.7), found in homozygous and heterozygous genotypes. In patients with α° phenotypes, other prevalent mutations were( _MED) and (_CAL/CAMP). The description of a sub-telomeric deletion in a patient with α-thalassemia and mental retardation was also achieved. ß-thalassemic mutations in heterozygous state were found in 7.6% of the patients, who presented α-thalassemic clinical features (microcytosis and Hb A2levels below 3.5%). Hematologic profiles for the α+ and α° genotypes were established for adult and pediatric patients. Hopefully, this work will provide guidelines for the detection of possible α-thalassemic carriers. It also highlights the collaborative work of hematologists, the biochemical and molecular biology laboratory and genetists, in order to provide appropriate genetic counseling.

Bases moleculares de alfa-talasemia en la Argentina

La α-talasemia, es uno de los desórdenes hereditarios más frecuentes mundialmente. Al presente, el diagnóstico molecular es la única herramienta que permite el diagnóstico certero. El propósito de este trabajo fue caracterizar las bases moleculares de estos síndromes en nuestro medio, y establecer relaciones genotipo-fenotipo. Mediante la complementación de distintas técnicas de biología molecular e hibridación fluorescente in situ (FISH), se logró poner en evidencia la presencia de mutaciones α-talasémicas en 145 de 184 (78.8%) pacientes estudiados con perfil hematológico compatible con α-talasemia. Dentro de este grupo, las deleciones correspondieron al defecto genético más frecuente, prevaleciendo la mutación -α3.7 en genotipos heterocigotas y homocigotas. Asimismo, en pacientes con fenotipo α0 las deleciones prevalentes fueron -MED y -CAL/CAMP. Este estudio permitió también describir una deleción de la región sub-telomérica en un paciente con α-talasemia y retraso mental. En el 7.6% de los pacientes caracterizados clínicamente como posibles α-talasémicos (microcitosis con valores de Hb A2 inferiores al 3.5%), se hallaron mutaciones β-talasémicas en estado heterocigota. Se lograron establecer perfiles hematológicos asociados a los genotipos α+ y α0 para pacientes adultos y niños. Esperamos que este trabajo pueda servir como guía para reconocer posibles portadores α-talasémicos. También permite destacar el trabajo en conjunto de médicos hematólogos, el laboratorio (bioquímico y de biología molecular) y de los médicos genetistas, con el fin de proporcionar adecuado consejo genético.(AU)

The α-thalassemia is one of the most common hereditary disorders worldwide. Currently, molecular diagnostics is the only available tool to achieve an accurate diagnosis. The purpose of this study was to characterize the molecular bases of these syndromes in our environment and to establish genotype-phenotype associations. Through a combination of different molecular techniques and fluorescent in situ hybridization (FISH),we were able to find α-thalassemic mutations in 145 of the 184 patients (78.8%) studied with hematological parameters compatible with α-thalassemia. Deletions of the a-globin genes resulted the major molecular cause of the disease, and the most frequent mutation was -α3.7, found in homozygous and heterozygous genotypes. In patients with α0 phenotypes, other prevalent mutations were -MED and -CAL/CAMP. The description of a sub-telomeric deletion in a patient with α-thalassemia and mental retardation was also achieved. β-thalassemic mutations in heterozygous state were found in 7.6% of the patients, who presented α-thalassemic clinical features (microcytosis and Hb A2 levels below 3.5%). Hematologic profiles for the α+ and α0 genotypes were established for adult and pediatric patients. Hopefully, this work will provide guidelines for the detection of possible α-thalassemic carriers. It also highlights the collaborative work of hematologists, the biochemical and molecular biology laboratory and genetists, in order to provide appropriate genetic counseling.(AU)

Bases moleculares de alfa-talasemia en la Argentina

La α-talasemia, es uno de los desórdenes hereditarios más frecuentes mundialmente. Al presente, el diagnóstico molecular es la única herramienta que permite el diagnóstico certero. El propósito de este trabajo fue caracterizar las bases moleculares de estos síndromes en nuestro medio, y establecer relaciones genotipo-fenotipo. Mediante la complementación de distintas técnicas de biología molecular e hibridación fluorescente in situ (FISH), se logró poner en evidencia la presencia de mutaciones α-talasémicas en 145 de 184 (78.8%) pacientes estudiados con perfil hematológico compatible con α-talasemia. Dentro de este grupo, las deleciones correspondieron al defecto genético más frecuente, prevaleciendo la mutación -α3.7 en genotipos heterocigotas y homocigotas. Asimismo, en pacientes con fenotipo α0 las deleciones prevalentes fueron -MED y -CAL/CAMP. Este estudio permitió también describir una deleción de la región sub-telomérica en un paciente con α-talasemia y retraso mental. En el 7.6% de los pacientes caracterizados clínicamente como posibles α-talasémicos (microcitosis con valores de Hb A2 inferiores al 3.5%), se hallaron mutaciones β-talasémicas en estado heterocigota. Se lograron establecer perfiles hematológicos asociados a los genotipos α+ y α0 para pacientes adultos y niños. Esperamos que este trabajo pueda servir como guía para reconocer posibles portadores α-talasémicos. También permite destacar el trabajo en conjunto de médicos hematólogos, el laboratorio (bioquímico y de biología molecular) y de los médicos genetistas, con el fin de proporcionar adecuado consejo genético.

The α-thalassemia is one of the most common hereditary disorders worldwide. Currently, molecular diagnostics is the only available tool to achieve an accurate diagnosis. The purpose of this study was to characterize the molecular bases of these syndromes in our environment and to establish genotype-phenotype associations. Through a combination of different molecular techniques and fluorescent in situ hybridization (FISH),we were able to find α-thalassemic mutations in 145 of the 184 patients (78.8%) studied with hematological parameters compatible with α-thalassemia. Deletions of the a-globin genes resulted the major molecular cause of the disease, and the most frequent mutation was -α3.7, found in homozygous and heterozygous genotypes. In patients with α0 phenotypes, other prevalent mutations were -MED and -CAL/CAMP. The description of a sub-telomeric deletion in a patient with α-thalassemia and mental retardation was also achieved. β-thalassemic mutations in heterozygous state were found in 7.6% of the patients, who presented α-thalassemic clinical features (microcytosis and Hb A2 levels below 3.5%). Hematologic profiles for the α+ and α0 genotypes were established for adult and pediatric patients. Hopefully, this work will provide guidelines for the detection of possible α-thalassemic carriers. It also highlights the collaborative work of hematologists, the biochemical and molecular biology laboratory and genetists, in order to provide appropriate genetic counseling.

Hb Wilde and Hb Patagonia: two novel elongated beta-globin variants causing dominant beta-thalassemia.

We describe here the molecular and hematological characteristics of novel frameshift mutations in exon 2 of the HBB gene (in heterozygous state) found in two Argentinean pediatric patients with dominant ß-thalassemia-like features. In Hb Wilde, HBB:c.270_273delTGAG(p.Glu90Cysfs*67), we detected the deletion of the third base of the codon 89 (T) and the codon 90 (GAG), whereas in Hb Patagonia, HBB:c.296_297dupGT(p.Asp99Trpfs*59), the frameshift mutation was due to a duplication of a 'GT' dinucleotide after the second base of codon 98 (GTG). The Hb Patagonia and Hb Wilde mutations would result in elongated ß-globin chains with modified C-terminal sequences and a total of 155 and 157 amino acids residues, respectively. Based on bioinformatics and structural analysis, as well as protein modeling, we predict that the elongated ß-globins would affect the formation of the αß dimers and their stability, which would further support the mechanism for the observed clinical features in both patients.

Coinheritance of a novel mutation on the HBA1 gene: c.187delG (p.W62fsX66) [codon 62 (-G) (α1)] with the α212 patchwork allele and Hb S [ß6(A3)Glu→Val, GAG>GTG; HBB: c.20A>T].

We describe a novel frameshift mutation on the HBA1 gene (c.187delG), causative of α-thalassemia (α-thal) in a Black Cuban family with multiple sequence variants in the HBA genes and the Hb S [ß6(A3)Glu→Val, GAG>GTG; HBB: c.20A>T] mutation. The deletion of the first base of codon 62 resulted in a frameshift at amino acid 62 with a putative premature termination codon (PTC) at amino acid 66 on the same exon (p.W62fsX66), which most likely triggers nonsense mediated decay of the resulting mRNA. This study also presents the first report of the α212 patchwork allele in Latin America and the description of two new sequence variants in the HBA2 region (c.-614G>A in the promoter region and c.95+39 C>T on the first intron).

Identification of a new HBA1 gene mutation (HBA1:c.301-2A>T) in cis with Hb Riccarton (HBA1:c.154G>A) [α51(CE9)Gly→Ser].

We report two point mutations found in a heterozygous state on the HBA1 gene of an 88-year-old Argentinean patient with an α(+)-thalassemia (α(+)-thal) phenotype: Hb Riccarton HBA1:c.154G>A) [α51(CE9)Gly→Ser] and a novel mutation, HBA1:c.301-2A>T that affects the splicing acceptor site of the second intron and leads to a non functional α-globin chain. Cloning of the HBA1 PCR (polymerase chain reaction) product and direct sequencing of the clones revealed that both mutations were in cis.

Two novel mutations in the thyroglobulin gene as cause of congenital hypothyroidism: identification a cryptic donor splice site in the exon 19.

Thyroglobulin (TG) is a homodimeric glycoprotein synthesized by the thyroid gland. To date, 52 mutations of the TG gene have been identified in humans. The purpose of the present study was to identify and characterize new mutations in the TG gene. We report a French patient with congenital hypothyroidism, mild enlarged thyroid gland and low levels of serum TG. Sequencing of DNA, genotyping, expression of chimeric minigenes as well as bioinformatics analysis were performed. DNA sequencing identified the presence of compound heterozygous mutations in the TG gene: the paternal mutation consists of a c.3788-3789insT or c.3788dupT, whereas the maternal mutation consists of g.IVS19+3_+4delAT. Minigene analysis of the g.IVS19+3_+4delAT mutant showed that the exon 19 is skipped during pre-mRNA splicing or partially included by use of cryptic 5' splice site located to 100 nucleotides downstream of the wild type exon-intron junction. The c.3788-3789insT mutation results in a putative truncated protein of 1245 amino acids, whereas g.IVS19+3_4delAT mutation originates two putative truncated proteins of 1330 and 1349 amino acids. In conclusion, we show that the g.IVS19+3_+4delAT mutation promotes the activation of a cryptic donor splice site in the exon 19 of the TG gene. These results open up new perspectives in the knowledge of the mechanism of splicing for the TG pre-mRNA.

Clinical and genetic characteristics in patients with Huntington's Disease from Argentina.

UNLABELLED: Huntington's Disease (HD) is a neurodegenerative disease, caused by the expansion of an unstable (CAG)(n) in the HTT gene. There is scarce data about the disease in Argentina. OBJECTIVE: To describe the demographic, clinical and molecular data in patients with HD from Argentina. PATIENTS AND METHODS: 59 HD patients were recruited at our department. Comprehensive interviews, neurological examination and genetic analysis were performed in probands. Statistical analysis was conducted using G-Stat 2.0 and non-parametric tests (Wilcoxon). RESULTS: 32 women and 27 men were diagnosed with a mean age of 45.7 ± 16.2 years and a mean age at onset of 35.8 ± 14.8 years. We found no gender prevalence and an inverse correlation between size of mutant CAG repeat sequence and age at onset, r = -0.58, r(2) = 33.6, Pearson's correlation coefficient p = 0.0008. Juvenile HD in this series of patients was higher than previously reported (16.6% vs. <10%). The mean CAG repeat in the expanded allele was 45.1. The number of CAG repeats in Argentinean controls was 17.8, which is similar to the literature of the European population. CONCLUSIONS: This is the first series of Argentinean HD patients with demographic, clinical and molecular data. Our findings appear similar to the ones described in Western European populations.

Investigación de la toxina microcistina en agua de red para consumo humano en tres plantas potabilizadoras de la provincia de Jujuy / Microcystin toxins in tap water for human consumption in three treatment plants of Jujuy provinc

INTRODUCCIÓN En una floración algal, Microcystis es el género más hallado y puede liberar la toxina microcistina al agua de red, poniendo en peligro la salud de la población abastecida si supera 1 µg/l (ppb). OBJETIVOS Determinar la presencia de Microcystis sp. y la concentración de microcistina en tres fuentes de captación y en el agua distribuida por tres plantas potabilizadoras, y generar así una base de datos aún inexistente para futuras investigaciones. MÉTODOS Se realizó un total de nueve muestreos en cada planta potabilizadora, donde se tomaron dos muestras mensuales en cámara de carga/fuente de captación y salida a consumo/planta potabilizadora. En ambas se investigó por microscopía directa la presencia de Microcystis sp. y por el método de Elisa la concentración de la toxina microcistina (µg/l o ppb). RESULTADOS En ninguna de las 48 muestras analizadas microscópicamente se halló el género Microcystis sp. Tampoco se encontraron concentraciones de la toxina microcistina superiores a 1ug/l (ppb). DISCUSIÓN Si bien los valores de concentración de microcistina hallados son menores a 1 ug/l (ppb), se deberá hacer un monitoreo continuo en las fuentes de captación para provisión de agua, a fin de tomar medidas cuando se produzca un aumento y evitar así un problema a nivel de salud pública.

Association of the TGrI29 microsatellite in thyroglobulin gene with autoimmune thyroiditis in a Argentinian population: a case-control study.

Autoimmune thyroid disease (AITD) is a multifactorial disorder that involves a putative association with thyroid autoantigen-specific and immune regulatory genes, as well as environmental factors. The thyroglobulin gene is the main identified thyroid autoantigen-specific gene associated to autoimmune thyroiditis. The aim of this work was to test for evidence of allelic association between autoimmune thyroiditis (AT) and thyroglobulin polymorphism markers in Argentinian patients. We studied six polymorphisms distributed throughout all the thyroglobulin gene: four microsatellites (Tgms1, Tgms2, TGrI29, and TGrI30), one insertion/deletion polymorphism (IndelTG-IVS18), and one exonic single nucleotide polymorphism (c.7589G>A) in 100 AT patients and 100 healthy control subjects. No differences in allele and genotype frequencies distribution were observed between autoimmune thyroiditis cases and controls for Tgms1, Tgms2, TGrI30, IndelTG-IVS18, and c.7589G>A. However, when we analyzed autoimmune thyroiditis patients with the TGrI29 microsatellite we found a significant association between the 197-bp allele and autoimmune thyroiditis (33.50% vs. 19.00% in control group) (P = 0.001). In addition, a significant major prevalence of the 197/201-bp genotype has been also seen in autoimmune thyroiditis subjects (59% vs. 24% in control group, P < 0.0001). In conclusion, our work showed the association between the thyroglobulin gene and autoimmune thyroiditis in Argentinian population and supports the described evidence of thyroglobulin as a thyroid-specific gene linked to AITD.

Two compound heterozygous mutations (c.215delA/c.2422T-->C and c.387delC/c.1159G-->A) in the thyroid peroxidase gene responsible for congenital goitre and iodide organification defect.

BACKGROUND: Iodide organification defects are frequently but not always associated with mutations in the thyroid peroxidase (TPO) gene and characterized by a positive perchlorate discharge test. These mutations phenotypically produce a congenital goitrous hypothyroidism, with an autosomal recessive mode of inheritance. OBJECTIVES: In the present study we extended our initial molecular studies in six unrelated patients heterozygous for the TPO mutations, in order to identify the second mutation in this autosomal recessive disease. METHODS: The promoter and the complete coding regions of the human TPO and DUOXA2 genes, along with the flanking regions of each intron were analysed by direct DNA sequencing. RESULTS: Four different inactivating TPO mutations were identified in two patients: two novel mutations (c.215delA [p.Q72fsX86] and c.1159G-->A [p.G387R]) and two previously reported (c.387delC [p.N129fsX208] and c.2422T-->C [p.C808R]), confirming the inheritance of two different compound heterozygous mutations, c.215delA/c.2422T-->C and c.387delC/c.1159G-->A. The remaining four patients did not show additional inactivating mutations in the TPO gene and all had only the wild type sequencing in the DUOXA2 gene. CONCLUSIONS: We have reported two patients with iodide organification defect caused by two compound heterozygous mutations, c.215delA/c.2422T-->C [p.Q72fsX86/p.C808R] and c.387delC/c.1159G-->A [p.N129fsX208/p.G387R], in the TPO gene and four patients with monoallelic TPO defect. Identification of the molecular basis of this disorder might be helpful for understanding the pathophysiology of congenital hypothyroidism.

Three mutations (p.Q36H, p.G418fsX482, and g.IVS19-2A>C) in the dual oxidase 2 gene responsible for congenital goiter and iodide organification defect.

BACKGROUND: Iodide organification defects are associated with mutations in the dual oxidase 2 (DUOX2) gene and are characterized by a positive perchlorate discharge test. These mutations produce a congenital goitrous hypothyroidism, usually transmitted in an autosomal recessive mode. METHODS: We studied the complete coding sequence of the human DUOX2 gene by single-strand conformational polymorphism (SSCP) analysis of DNA from 17 unrelated patients with iodide organification defects. Samples showing an aberrant pattern were directly sequenced. All mutations were validated by SSCP analysis. Finally, the effect of a splicing mutation was studied by construction of minigenes. RESULTS: Genomic DNA sequencing revealed 3 novel mutations [c.108G>C (p.Q36H), c.1253delG (p.G418fsX482), and g.IVS19-2A>C] and 1 previously reported mutation [c.2895-2898delGTTC (p.S965fsX994)] in 2 families with 1 (family 1) and 2 (family 2) affected members. This implies the inheritance of 2 compound heterozygous mutations, p.Q36H and p.S965fsX994 in family 1 and p.G418fsX482 and g.IVS19-2A>C in family 2. The c.1253delG mutation was associated with a c.1254C>A transversion. In vitro transcription analysis showed that exon 20 is skipped entirely when the g.IVS19-2A>C mutation is present. The wild-type glutamine residue at position 36 is strictly conserved. CONCLUSIONS: Two previously unknown compound heterozygous mutations in the DUOX2 gene, p.Q36H/p.S965fsX994 and p.G418fsX482/g.IVS19-2A>C, are responsible for iodide organification defects in 2 unrelated families. Identification of the molecular basis of this disorder might be helpful for understanding the pathophysiology of this congenital hypothyroidism.

[The thyroid as a model for molecular mechanisms in genetic diseases]. / La tiroides como modelo de mecanismos moleculares en enfermedades geneticas.

Thyroid diseases constitute a heterogeneous collection of abnormalities associated with mutations in genes responsible for the development of thyroid: thyroid transcription factor-1 (TTF-1), thyroid transcriptions factor-2 (TTF-2) and PAX8, or in one of the genes coding for the proteins involved in thyroid hormone biosynthesis such as thyroglobulin (TG), thyroperoxidase (TPO), hydrogen peroxide-generating system (DUOX2), sodium/iodide symporter (NIS), pendrin (PDS), TSH and TSH receptor (TSHr). Congenital hypothyroidism occurs with a prevalence of 1 in 4000 newborns. Patients with this syndrome can be divided into two groups: nongoitrous (dysem/bryogenesis) or goitrous (dyshormonogenesis) congenital hypothyroidism. The dysembryogenesis group, which accounts for 85% of the cases, results from ectopy, agenesis and hypoplasia. In a minority of these patients, the congenital hypothyroidism is associated with mutations in TTF-1, TTF-2, PAX-8, TSH or TSHr genes. The presence of congenital goiter (15% of the cases) has been linked to mutations in the NIS, TG, TPO, DUOX2 or PDS genes. The congenital hypothyroidism with dyshormonogenesis is transmitted as an autosomal recessive trait. Somatic mutations of the TSHr have been identified in hyperfunctioning thyroid adenomas. Another established thyroid disease is the resistance to thyroid hormone (RTH). It is a syndrome of reduced tissue responsiveness to hormonal action caused by mutations located in the thyroid hormone receptor beta (TRbeta) gene. Mutant TRbetas interfere with the function of the wild-type receptor by a dominant negative mechanism. In conclusion, the identification of mutations in the thyroid expression genes has provided important insights into structure-function relationships. The thyroid constitutes an excellent model for the molecular study of genetic diseases.

A new case of congenital goiter with hypothyroidism caused by a homozygous p.R277X mutation in the exon 7 of the thyroglobulin gene: a mutational hot spot could explain the recurrence of this mutation.

Identification of thyroglobulin (TG) gene mutations may provide insight into the structure-function relationship. In this study, we have performed molecular studies in a patient with congenital goiter, hypothyroidism, and impairment of TG synthesis. Genomic DNA sequencing revealed a homozygous c.886C-->T mutation in exon 7, resulting in a premature stop codon at amino acid 277 (p.R277X). The same nonsense mutation had been reported previously in two Brazilian families with multiple occurrence of congenital hypothyroidism with goiter. We compared the insertion/deletion polymorphism in intron 18, microsatellites (Tgm1, Tgm2, TGrI29, and TGrI30), and exonic single-nucleotide polymorphism haplotypes identified in the patient with a member of the previously reported family, who also carry the mutation as a compound heterozygous mutation. The single-nucleotide polymorphism and microsatellite analysis revealed that the two affected individuals do not share a common TG allele. This suggests that the p.R277X mutation is a mutational hot spot. No difference in either splicing or abundance of the amplified product was detected by RT-PCR, excluding that an alternative splicing mechanism, by skipping of exon 7, would restore the normal reading frame. In conclusion, we report a new case of congenital goiter and hypothyroidism caused by a p.R277X mutation in the TG gene. Moreover, we show that nucleotide 886 is a mutational hot spot that explains the recurrence of this mutation.