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  • Author: Marianna Di Frenna x
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Tiziana de Filippis Laboratory of Endocrine and Metabolic Research, Milan, Italy
Division of Endocrinology and Metabolic Diseases, IRCCS Istituto Auxologico Italiano, Milan, Italy

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Federica Marelli Laboratory of Endocrine and Metabolic Research, Milan, Italy
Division of Endocrinology and Metabolic Diseases, IRCCS Istituto Auxologico Italiano, Milan, Italy

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Maria Cristina Vigone Department of Pediatrics, Vita-Salute University, San Raffaele Scientific Institute, Milan, Italy

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Marianna Di Frenna Department of Pediatrics, Vita-Salute University, San Raffaele Scientific Institute, Milan, Italy

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Giovanna Weber Department of Pediatrics, Vita-Salute University, San Raffaele Scientific Institute, Milan, Italy

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Luca Persani Laboratory of Endocrine and Metabolic Research, Milan, Italy
Division of Endocrinology and Metabolic Diseases, IRCCS Istituto Auxologico Italiano, Milan, Italy
Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy

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Objectives: To verify the involvement of NKX2-1 gene in infants with brain-lung-thyroid (BLT) syndrome and hypothyroid phenotypes variable among congenital hypothyroidism (CH) or idiopathic mild hypothyroidism (IMH) of postnatal onset. Methods: The candidates were selected by a case-finding approach in 130 CH and 53 IMH infants. The NKX2-1 gene was analyzed by direct sequencing and multiplex ligation-dependent probe amplification. The variants were studied in vitro, by expression analyses and luciferase bioassay. Results: Four cases (3 CH and 1 IMH) consistent with BLT syndrome were identified. Two children were affected with respiratory distress and CH, but wild-type NKX2-1 gene. The remaining two presented choreic movements and no pulmonary involvement, but discrepant thyroid phenotypes: one had severe CH with lingual ectopy and the other one IMH with gland in situ. They were carriers of new de novo heterozygous frameshift mutations of NKX2-1 (c.177delG and c.153_166del14). The c.177delG leads to a prematurely truncated protein (p.H60TfsX11) with undetectable activity in vitro. The c.153_166del14 leads to the generation of an elongated aberrant protein (p.A52RfsX351) able to translocate into the nucleus, but completely inactive on a responsive promoter. Conclusions: Two novel heterozygous frameshift mutations of NKX2-1 were identified in 2 cases selected on the basis of a BLT-like phenotype among 183 hypothyroid infants. The atypical hypothyroid phenotypes of these 2 children (CH with lingual ectopy or IMH of postnatal onset) further expand the clinical spectrum that can be associated with NKX2-1 mutations.

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