Tratamiento con TRIAC en pacientes pediátricos con deficiencia de MCT8 / Treatment with TRIAC in pediatric patients with MCT8

Los transportadores de monocarboxilatos (MCT) permiten el ingreso celular de hormonas tiroideas, especialmente en el sistema nervioso central (SNC), donde son indispensables para el neurodesarrollo. La deficiencia de MCT8 produce la combinación de hipotiroidismo en SNC e hipertiroidismo periférico, caracterizada por T3 elevada. El único tratamiento actualmente disponible es el ácido 3,3',5-triyodotiroacético (TRIAC), un análogo de hormonas tiroideas que tiene como objetivo mejorar la tirotoxicosis periférica y prevenir la progresión del deterioro neurológico. En el presente artículo, se evalúan las características clínicas, imagenológicas, bioquímicas y genéticas de 4 pacientes con deficiencia de MCT8 tratados con TRIAC hasta la fecha, las dosis utilizadas y la respuesta al tratamiento.

Monocarboxylate transporters (MCTs) allow the cellular entry of thyroid hormones, especially into the central nervous system (CNS), where they are crucial for neurodevelopment. MCT8 deficiency results in the combination of hypothyroidism in the CNS and peripheral hyperthyroidism, characterized by elevated T3 levels. The only treatment currently available is 3,3',5-triiodothyroacetic acid (TRIAC), a thyroid hormone analogue aimed at improving peripheral thyrotoxicosis and preventing the progression of neurological impairment. Here we assess the clinical, imaging, biochemical, and genetic characteristics of 4 patients with MCT8 deficiency who have received TRIAC to date, the doses used, and the response to treatment.

Treatment with TRIAC in pediatric patients with MCT8. / Tratamiento con TRIAC en pacientes pediátricos con deficiencia de MCT8.

Monocarboxylate transporters (MCTs) allow the cellular entry of thyroid hormones, especially into the central nervous system (CNS), where they are crucial for neurodevelopment. MCT8 deficiency results in the combination of hypothyroidism in the CNS and peripheral hyperthyroidism, characterized by elevated T3 levels. The only treatment currently available is 3,3',5-triiodothyroacetic acid (TRIAC), a thyroid hormone analogue aimed at improving peripheral thyrotoxicosis and preventing the progression of neurological impairment. Here we assess the clinical, imaging, biochemical, and genetic characteristics of 4 patients with MCT8 deficiency who have received TRIAC to date, the doses used, and the response to treatment.

Los transportadores de monocarboxilatos (MCT) permiten el ingreso celular de hormonas tiroideas, especialmente en el sistema nervioso central (SNC), donde son indispensables para el neurodesarrollo. La deficiencia de MCT8 produce la combinación de hipotiroidismo en SNC e hipertiroidismo periférico, caracterizada por T3 elevada. El único tratamiento actualmente disponible es el ácido 3,3',5-triyodotiroacético (TRIAC), un análogo de hormonas tiroideas que tiene como objetivo mejorar la tirotoxicosis periférica y prevenir la progresión del deterioro neurológico. En el presente artículo, se evalúan las características clínicas, imagenológicas, bioquímicas y genéticas de 4 pacientes con deficiencia de MCT8 tratados con TRIAC hasta la fecha, las dosis utilizadas y la respuesta al tratamiento.

Respuesta al lenvatinib en una paciente pediátrica con insuficiencia respiratoria secundaria a carcinoma papilar de tiroides / Response to lenvatinib in a pediatric patient with respiratory failure associated with papillary thyroid carcinoma

El cáncer papilar de tiroides es el tumor tiroideo más común en la infancia. En estadios avanzados, puede presentarse con cuadro de insuficiencia respiratoria. El tratamiento de elección es la tiroidectomía total y iodo radiactivo. En tumores irresecables, se debería considerar terapia con inhibidores multicinasa.Niña de 10 años de edad derivada por insuficiencia respiratoria progresiva. Se realizó el diagnóstico de cáncer papilar de tiroides con metástasis pulmonares. Por presentar un tumor irresecable no pasible de cirugía, se indicó el uso compasivo de lenvatinib, que mostró una rápida y favorable respuesta clínica con resolución de la insuficiencia respiratoria al noveno día del tratamiento.El diagnóstico temprano de cáncer papilar de tiroides previene la grave morbilidad respiratoria ocasionada por diagnósticos tardíos. Podría considerarse el uso de lenvatinib como alternativa previa a las terapias de primera línea (cirugía e iodo radiactivo) en casos de enfermedad con gran compromiso local y a distancia.

Papillary thyroid cancer is the most common thyroid tumor in childhood. In advanced stages, it can present with respiratory failure. The treatment of choice is total thyroidectomy and radioactive iodine. In cases of unresectable tumors, therapy with multikinase inhibitors should be considered. A 10-year-old girl was referred for progressive respiratory failure. A diagnosis of papillary thyroid cancer with pulmonary metastases was made. Due to the presence of an unresectable tumor not subject to surgery, the compassionate use of lenvatinib was indicated, showing a rapid and favorable clinical response with resolution of respiratory failure on the ninth day.Early diagnosis of papillary thyroid cancer prevents severe respiratory morbidity caused by late diagnoses. The use of lenvatinib should be considered as a previous step towards first-line therapies (surgery and radioactive iodine) in cases with great local and distant involvement.

[Response to lenvatinib in a pediatric patient with respiratory failure associated with papillary thyroid carcinoma]. / Respuesta al lenvatinib en una paciente pediátrica con insuficiencia respiratoria secundaria a carcinoma papilar de tiroides.

Papillary thyroid cancer is the most common thyroid tumor in childhood. In advanced stages, it can present with respiratory failure. The treatment of choice is total thyroidectomy and radioactive iodine. In cases of unresectable tumors, therapy with multikinase inhibitors should be considered. A 10-year-old girl was referred for progressive respiratory failure. A diagnosis of papillary thyroid cancer with pulmonary metastases was made. Due to the presence of an unresectable tumor not subject to surgery, the compassionate use of lenvatinib was indicated, showing a rapid and favorable clinical response with resolution of respiratory failure on the ninth day. Early diagnosis of papillary thyroid cancer prevents severe respiratory morbidity caused by late diagnoses. The use of lenvatinib should be considered as a previous step towards first-line therapies (surgery and radioactive iodine) in cases with great local and distant involvement.

El cáncer papilar de tiroides es el tumor tiroideo más común en la infancia. En estadios avanzados, puede presentarse con cuadro de insuficiencia respiratoria. El tratamiento de elección es la tiroidectomía total y iodo radiactivo. En tumores irresecables, se debería considerar terapia con inhibidores multicinasa. Niña de 10 años de edad derivada por insuficiencia respiratoria progresiva. Se realizó el diagnóstico de cáncer papilar de tiroides con metástasis pulmonares. Por presentar un tumor irresecable no pasible de cirugía, se indicó el uso compasivo de lenvatinib, que mostró una rápida y favorable respuesta clínica con resolución de la insuficiencia respiratoria al noveno día del tratamiento. El diagnóstico temprano de cáncer papilar de tiroides previene la grave morbilidad respiratoria ocasionada por diagnósticos tardíos. Podría considerarse el uso de lenvatinib como alternativa previa a las terapias de primera línea (cirugía e iodo radiactivo) en casos de enfermedad con gran compromiso local y a distancia.

Variables predictivas de talla baja adulta en pacientes con hipotiroidismo adquirido grave de origen autoinmune / Predictive outcome measures of adult short stature in patients with severe acquired autoimmune hypothyroidism

El hipotiroidismo por tiroiditis de Hashimoto es la causa más frecuente de disfunción tiroidea en niños.Nuestro objetivo fue analizar el impacto en la talla final según la talla y el estadio puberal al momento del diagnóstico en menores de 18 años con hipotiroidismo grave de origen autoinmune. De los 79 pacientes, el 78,5 % fueron mujeres. Los que presentaron bocio (el 56 %) mostraron mejor talla en el diagnóstico que los que no lo tenían (puntaje de desvío estándar de media de talla: 0,2 vs. -2,42; p < 0,0001). Cinco niñas (el 6,3 %) presentaron pubertad precoz. De los pacientes con talla final (n: 33), dentro de los que presentaron talla baja al momento del diagnóstico, los púberes tuvieron una talla final significativamente menor que los prepúberes (puntaje de desvío estándar media: -2,82 vs. -1,52; p = 0,0311).El diagnóstico tardío de hipotiroidismo grave en pediatría tiene un impacto negativo en la talla final, especialmente, en los pacientes puberales al momento del diagnóstico.

Hypothyroidism caused by Hashimoto's thyroiditis is the most common reason for thyroid dysfunction in children. Our objective was to analyze its impact on final stature in relation to height and pubertal stage at the time of diagnosis in children younger than 18 years with severe autoimmune hypothyroidism. Out of 79 patients, 78.5 % were girls. Those with goiter (56 %) had a better height at diagnosis than those without goiter (mean standard deviation score for height: 0.2 versus −2.42; p < 0.0001). Five girls (6.3 %) had precocious puberty. When considering the final stature of patients (n: 33), among those with short stature at the time of diagnosis, pubertal children had a significantly shorter final stature than prepubertal children (mean standard deviation score for height: −2.82 versus −1.52; p = 0.0311). The late diagnosis of severe hypothyroidism in pediatrics has a negative impact on final stature, especially in those who were pubertal patients at the time of diagnosis

Predictive outcome measures of adult short stature in patients with severe acquired autoimmune hypothyroidism. / Variables predictivas de talla baja adulta en pacientes con hipotiroidismo adquirido grave de origen autoinmune.

Hypothyroidism caused by Hashimoto's thyroiditis is the most common reason for thyroid dysfunction in children. Our objective was to analyze its impact on final stature in relation to height and pubertal stage at the time of diagnosis in children younger than 18 years with severe autoimmune hypothyroidism. Out of 79 patients, 78.5 % were girls. Those with goiter (56 %) had a better height at diagnosis than those without goiter (mean standard deviation score for height: 0.2 versus -2.42; p < 0.0001). Five girls (6.3 %) had precocious puberty. When considering the final stature of patients (n: 33), among those with short stature at the time of diagnosis, pubertal children had a significantly shorter final stature than prepubertal children (mean standard deviation score for height: -2.82 versus -1.52; p = 0.0311). The late diagnosis of severe hypothyroidism in pediatrics has a negative impact on final stature, especially in those who were pubertal patients at the time of diagnosis.

El hipotiroidismo por tiroiditis de Hashimoto es la causa más frecuente de disfunción tiroidea en niños. Nuestro objetivo fue analizar el impacto en la talla final según la talla y el estadio puberal al momento del diagnóstico en menores de 18 años con hipotiroidismo grave de origen autoinmune. De los 79 pacientes, el 78,5 % fueron mujeres. Los que presentaron bocio (el 56 %) mostraron mejor talla en el diagnóstico que los que no lo tenían (puntaje de desvío estándar de media de talla: 0,2 vs. -2,42; p < 0,0001). Cinco niñas (el 6,3 %) presentaron pubertad precoz. De los pacientes con talla final (n: 33), dentro de los que presentaron talla baja al momento del diagnóstico, los púberes tuvieron una talla final significativamente menor que los prepúberes (puntaje de desvío estándar media: -2,82 vs. -1,52; p = 0,0311). El diagnóstico tardío de hipotiroidismo grave en pediatría tiene un impacto negativo en la talla final, especialmente, en los pacientes puberales al momento del diagnóstico.

Debilidad muscular con hipokalemia e hipertiroidismo en un adolescente con síndrome de Down / Muscle weakness with hypokalemia and hyperthyroidism in an adolescent with Down syndrome

La hipokalemia aguda es una causa poco frecuente de debilidad muscular. La parálisis periódica tirotóxica es una complicación infrecuente de la tirotoxicosis, en sus diferentes etiologías, en la cual se produce hipokalemia por un flujo masivo de potasio al compartimiento intracelular, que provoca parálisis muscular, que afecta, principalmente, la musculatura proximal de los miembros inferiores. Es importante reconocer esta entidad para instaurar un tratamiento adecuado que incluya el rápido suplemento de potasio y el uso de beta-bloqueantes no selectivos. El tratamiento del hipertiroidismo subyacente y el retorno al estado eutiroideo es imprescindible para la resolución de los episodios de parálisis periódica tirotóxica. Aquí se presenta a un paciente de 13 años de edad con síndrome de Down que consultó por debilidad muscular de los miembros inferiores y trastorno de la marcha, asociada a hipokalemia aguda, en el que se realizó el diagnóstico de hipertiroidismo por enfermedad de Graves.

Acute hypokalemic paralysis is a rare cause of acute weakness. Thyrotoxic periodic paralysis (TPP) is an unusual complication of hyperthyroidism. It is characterized by sudden onset of hypokalemia condition resulting from a shift of potassium into cells and paralysis that primarily affects the lower extremities. Failure to recognize TPP may lead to improper management. Treatment of TPP includes replacing potassium rapidly, using nonselective beta-blockers and correcting the underlying hyperthyroidism as soon as possible. TPP is curable once euthyroid state is achieved. We describe a 13-year-old male with Down syndrome who presented with acute onset of lower extremity weakness secondary to acute hypokalemia and was found to have new onset Graves' disease.

[Muscle weakness with hypokalemia and hyperthyroidism in an adolescent with Down syndrome]. / Debilidad muscular con hipokalemia e hipertiroidismo en un adolescente con síndrome de Down.

Acute hypokalemic paralysis is a rare cause of acute weakness. Thyrotoxic periodic paralysis (TPP) is an unusual complication of hyperthyroidism. It is characterized by sudden onset of hypokalemia condition resulting from a shift of potassium into cells and paralysis that primarily affects the lower extremities. Failure to recognize TPP may lead to improper management. Treatment of TPP includes replacing potassium rapidly, using nonselective beta-blockers and correcting the underlying hyperthyroidism as soon as possible. TPP is curable once euthyroid state is achieved. We describe a 13-year-old male with Down syndrome who presented with acute onset of lower extremity weakness secondary to acute hypokalemia and was found to have new onset Graves' disease.

La hipokalemia aguda es una causa poco frecuente de debilidad muscular. La parálisis periódica tirotóxica es una complicación infrecuente de la tirotoxicosis, en sus diferentes etiologías, en la cual se produce hipokalemia por un flujo masivo de potasio al compartimiento intracelular, que provoca parálisis muscular, que afecta, principalmente, la musculatura proximal de los miembros inferiores. Es importante reconocer esta entidad para instaurar un tratamiento adecuado que incluya el rápido suplemento de potasio y el uso de beta-bloqueantes no selectivos. El tratamiento del hipertiroidismo subyacente y el retorno al estado eutiroideo es imprescindible para la resolución de los episodios de parálisis periódica tirotóxica. Aquí se presenta a un paciente de 13 años de edad con síndrome de Down que consultó por debilidad muscular de los miembros inferiores y trastorno de la marcha, asociada a hipokalemia aguda, en el que se realizó el diagnóstico de hipertiroidismo por enfermedad de Graves.

Second Neoplasms in Children Following a Treatment for Acute Leukemia and/or Lymphoma: 29 Years of Experience in a Single Institution in Argentina.

INTRODUCTION: Childhood acute leukemias (AL) and lymphomas achieve good survival rates. However, second neoplasms (SN) are a devastating event. METHODS: From August 1987 to December 2016, 34 of 3321 (1%) patients with diagnosis of AL or lymphoma developed SN. SN were AL (n=16), CNS tumors (n=5), endocrinal tumors (n=3), lymphomas (n=2), schwannoma (n=2) assorted sarcomas (n=4), retinal melanoma (n=1), and Vanek tumor (n=1). Median latency was 51 (range, 10 to 110) months for hematological malignancies and 119 (range, 25 to 236) months for solid tumors (P=0.001). RESULTS: A total of 33 patients with SN were treated taking into account cumulative doses of anthracyclines and radiotherapy. Twenty-three (67.6%) patients achieved complete remission (CR), 5 died early during therapy and 5 were refractory or partial responders. Six patients presented relapses of the SN and 1 died in CR. Seventeen patients remain alive in CR, with a median follow-up of 110 (range, 4 to 276) months. CONCLUSIONS: (1) The latency period was significantly longer for patients developing solid tumors than for those developing AL. (2) AL was the most frequent SN. (3) Our results strongly encourage giving standard therapy to SN, considering cumulative doses of previous treatment, since similar probabilities of surviving as "de novo" counterparts can be achieved.

Age-specific thyroid hormone and thyrotropin reference intervals for a pediatric and adolescent population.

BACKGROUND: Establishment of reliable reference intervals remains valuable for confirming validity and advancing standardization across methods and populations. Moreover, knowledge of the measurement uncertainty (U) and of the reference change value (RCV) has important applications in clinical chemistry. METHODS: Starting from the information available in the laboratory data base (29,901 subjects) an initial selection was carried out by eliminating all subjects with a clinical or laboratory pathological report; data from 7581 0- to 20-year-old subjects (53.87% girls) remained in the study. These subjects, divided into nine age groups, were used to define reference distribution percentiles (2.5th, 50th and 97.5th) of serum thyrotropin (TSH), triiodothyronine (T3), thyroxine (T4), and free T4 (fT4), as well as U and RCV of these assays. RESULTS: In early infancy, T4 and fT4 values were higher than in the older age groups. Serum T4 95th percentile reference value, useful for the diagnosis of hyperthyroidism, was 142.9 in 20-year-old boys and 230.4 nmol/L in early infants and serum T3 95th percentile was 2.6 and 3.5 nmol/L, respectively, while fT4 2.5th percentile reference value, useful for the diagnosis of hypothyroidism, was 9.6 and 13.0 pmol/L, respectively. Serum TSH 97.5th percentile showed less age variation, 4.38-4.88 mIU/L. Performance of the four assays resulted in approximately 20% Us, reflecting simple and complex imprecision, trueness, analytical and functional sensitivity. RCV of serum TSH (58.6%) was larger than for thyroid hormones (28.3%-34.7%), probably due to the high biological variation of this hormone. CONCLUSIONS: We have established reference interval for TSH and thyroid hormones, as well as Us for assessing reliability of measurements, and RCVs to alert users on the presence of clinical significant changes.

Evaluation and clinical application of changes in thyroid hormone and TSH levels in critically ill full-term newborns.

INTRODUCTION: The term "euthyroid sick syndrome" (ESS) has been used to describe a pattern of thyroid hormone changes during the course of critical illness in adult patients without thyroid disease, often associated with reduced thyroid hormone secretion. OBJECTIVE: To describe the thyroid hormone profile in full-term newborns critically ill compared with thyroid hormone profile of healthy infants, and determine if alterations could be related to the severity of the disease and outcome. METHODS: A cross-sectional, observational, and prospective study of full-term infants admitted to the neonatal intensive care unit (NICU) of the Hospital de Pediatría J.P. Garrahan between July 2007 and April 2008. Serum T3, T4, and thyroid stimulating hormone (TSH) levels were measured at admission and severity of the disease was evaluated through SNAP, lactic acid, respiratory assistance and number of organs affected. RESULTS: Sick newborns showed significantly lower T3 and T4 levels compared with healthy infants [T3: -0.97 µg/dL (95% CI -0.89, -1.13) and T4: -4.37 µg/dL (95% CI -2.95, -5.78)]. Only 29 out of 94 (31%) infants presented a normal profile; 37 (39%) infants showed isolated low T3 levels, 20 (21%) infants had low T3 and T4 levels and eight (9%) infants had low TSH, T3, and T4. Of this latter group, five of eight (62%) children died suggesting a significantly higher risk of death for patients with low T3 associated with low T4 and TSH [Risk ratio (RR) 10.75 95% CI 3.93, 29]. CONCLUSIONS: Full-term sick newborns frequently have lower thyroid hormone levels than healthy ones. These observed thyroid hormones changes might be related to the underlying disease and could be used as a prognostic marker of the severity and fatal outcome of the patient.

Two novel mutations of the TSH-beta subunit gene underlying congenital central hypothyroidism undetectable in neonatal TSH screening.

CONTEXT: Patients with TSH-beta subunit defects and congenital hypothyroidism are missed by TSH-based neonatal screening. OBJECTIVE: Our objective was to report the molecular consequences of a novel splice-junction mutation and a novel missense mutation in the TSH-beta subunit gene found in two patients with congenital central hypothyroidism and conventional treatment-resistant anemia. RESULTS: Patient 1 had a homozygous G to A nucleotide change at the 5' donor splice site of exon/intron 2. This resulted in a silent change at codon 34 of the mature protein. In vitro splicing assays showed that the mutant minigene dramatically affected pre-mRNA processing, causing exon 2 to be completely skipped. The putative product from a new out-of-frame translational start point in exon 3 is expected to yield a nonsense 25-amino-acid peptide. In patient 2, sequence analysis revealed a compound heterozygosis for the already reported 313delT (C105Vfs114X) mutation and for a second novel mutation in exon 3, substituting G for A at cDNA nucleotide position 323, resulting in a C88Y change. This cysteine residue is conserved among all dimeric pituitary and placental glycoprotein hormone-beta subunits. Data from in silico analysis confirmed that the C88Y mutation would affect subunit conformation. Indeed, two different bioinformatics approaches, PolyPhen and SIFT analysis, predicted C88Y to be a damaging substitution. CONCLUSIONS: In isolated TSH deficiency, the exact molecular diagnosis is mandatory for diagnosis of isolated pituitary deficiency, delineation of prognosis, and genetic counseling. Moreover, diagnosis of central hypothyroidism should be considered in the face of severe infant anemia of uncertain etiology.

Thyroid axis dysfunction in patients with Prader-Willi syndrome during the first 2 years of life.

INTRODUCTION: Prader-Willi syndrome (PWS) is a genetic disorder caused by the loss of expression of paternally transcribed genes in a highly imprinted region of chromosome 15q11-13. The clinical phenotype has been well characterized, mostly related to hypothalamic dysfunction. Even though central hypothyroidism has been documented in 20-30% of patients with PWS, thyroid function during the first 2 years of life has not been clearly defined. OBJECTIVE: To evaluate hypothalamic-pituitary-thyroid function in infant PWS patients. STUDY DESIGN: Eighteen patients with PWS, aged 0.16-2 years, were included in a prospective study. PWS diagnosis was based on clinical features and molecular analysis. Serum total (T) T4, free (F) T4, T3 and thyroid-stimulating hormone (TSH) were evaluated in the patients with PWS included in the study. Serum hormone values were compared to those of a large reference population of the same age. RESULTS: In 13 of 18 patients with PWS (72.2%), serum TT4 and/or FT4 levels were below the 2.5th percentile of the reference population, while in only one PWS patient serum T3 was below this cut-off. CONCLUSION: The results of this study suggest that transient or definitive thyrotropin-releasing hormone (TRH)-TSH thyroid axis dysfunction may frequently be present in infant PWS patients. Paediatricians should be aware of this dysfunction in this critical period of thyroid hormone action on neurological development.

Genotyping of resistance to thyroid hormone in South American population. Identification of seven novel missense mutations in the human thyroid hormone receptor beta gene.

Thyroid Hormone Receptor beta (THRB) defects, typically transmitted as autosomal dominant traits, cause Resistance to Thyroid Hormone (RTH). We analyzed the THRB gene in thirteen South American patients with clinical evidence RTH from eleven unrelated families. Sequence analysis revealed seven novel missense mutations. Four novel mutations were identified in exon 9. The first, a c.991A>G transition which originates a substitution of asparagine by aspartic acid (p.N331D). The second nucleotide alteration consists of a guanine to cytosine transversion at position 1003 (c.1003G>C) and results in substitution of the alanine at codon 335 by proline (p.A335P). The third mutation, a c.1022T>C transition produces a change of leucine by proline (p.L341P). The fourth mutation detected in exon 9 was a c.1036C>T transition which replaces the leucine at codon 346 by phenylalanine (p.L346F). The sequencing of the exon 10 detected three novel missense mutations. The first, a c.1293A>G transition changing isoleucine 431 for methionine (p.I431M). The second, the cytosine at position 1339 was replaced by adenine (c.1339C>A) resulting in the replacement of proline by threonine (p.P447T). The third mutation detected in exon 10 was a c.1358C>T transition resulting in the substitution of proline at codon 453 by leucine (p.P453L). Finally, sequencing analysis of the THRB gene revealed three substitutions previously described (p.A268G, p.P453T and p.F459C). The p.P453T was found in two patients. In conclusion, we report thirteen patients with RTH caused by heterozygous mutations of the THRB gene. Seven of the identified mutations correspond to novel substitutions.

Identification and characterization of four PAX8 rare sequence variants (p.T225M, p.L233L, p.G336S and p.A439A) in patients with congenital hypothyroidism and dysgenetic thyroid glands.

CONTEXT: Thyroid dysgenesis may be associated with mutations in the paired box transcription factor 8 (PAX8) gene and is characterized by congenital hypothyroidism transmitted in an autosomal dominant mode. OBJECTIVES: The aim of this study was to identify new mutations in the PAX8 gene. Sixty congenital hypothyroidism-affected individuals with dysgenetic (agenesis, ectopia and hypoplasia) and eutopic thyroid glands were studied. METHODS: The 12 exons of the PAX8 gene along with their exon-intron boundaries were amplified from genomic DNA and a mutational screening was performed by single-strand conformational polymorphism (SSCP) followed by direct sequencing of samples with abnormal migration patterns. The PAX8 mutations were functionally characterized by transient transfection experiments. RESULTS: Molecular analysis of the PAX8 gene indicated that four affected individuals had four sequence differences: three novel variations [c.699C>T (p.L233L), c.1006G>A (p.G336S) and c.1317A>G (p.A439A)] and one recently reported [c.674C>T (p.T225M)], whereas the 56 remaining patients showed only wild-type alleles of PAX8. p.T225M, p.L233L and p.G336S variants were not detected in 530 chromosomes from 265 subjects randomly selected from the general population, whereas the p.A439A variant was identified in only one of the 530 chromosomes analysed. Functional analysis of the nonsynonymous substitutions showed that the p.T225M and p.G336S proteins had not lost their ability to bind a specific DNA sequence and to activate the transcription of the thyroglobulin (TG) promoter in synergy with thyroid transcription factor 1 (TTF1). CONCLUSIONS: We report the occurrence of two nonsynonymous substitutions, one recently reported (p.T225M) and one novel (p.G336S), and two novel synonymous substitutions (p.L233L and p.A439A) in the PAX8 gene. p.T225M and p.G336S are rare sequence variants or may act by inhibiting an unknown particular function. Our study also confirms the very low prevalence of PAX8 mutations in thyroid dysgenesis.

The C105fs114X is the prevalent thyrotropin beta-subunit gene mutation in Argentinean patients with congenital central hypothyroidism.

BACKGROUND: Congenital isolated thyrotropin (TSH) deficiency is an unusual condition characterized by low levels of thyroid hormones and TSH, usually presenting early typical signs of severe hypothyroidism. Five different beta-TSH mutations have been described so far. While 4 of them affect only consanguineous families, a frameshift mutation in exon 3 (C105fs114X) has been found also in nonconsanguineous families. OBJECTIVE: The aim of the present study was to characterize beta-TSH mutations in Argentinean patients with congenital central hypothyroidism (CCH) and to emphasize the importance of early biochemical and molecular diagnosis of this disorder. PATIENTS AND METHODS: We investigated 8 Argentinean children (3 boys, 5 girls) from 7 unrelated families with CCH based upon low levels of T(4) and T(3), and low basal and stimulated TSH levels. Mutation characterizations for the beta-TSH gene were performed by PCR amplification followed by sequence and restriction enzyme analysis with SNABI in the patients, 9 parents and in 100 newborn children. RESULTS: All patients presented the same homozygous mutation in exon 3 of the beta-TSH gene (C105fs114X), the 9 studied parents were heterozygous for the same mutation and 1 carrier was found in the 100 studied newborns. CONCLUSION: Our findings show that the C105fs114X mutation is prevalent in our population and may constitute a hot spot at codon 105 in the beta-TSH gene. Since this mutation is easily demonstrable by a SNABI digestion in DNA amplified from dried blood spots, its investigation would be indicated in patients in our milieu with clinical and biochemical features of CCH, allowing early L-thyroxine (LT(4)) replacement and genetic counseling of the family.