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CLINICAL STUDY |
Unidade de Genética Molecular, 1 Unidade de Consulta and 2 Comissão Nacional de Diagnóstico Precoce, Instituto de Genética Médica Jacinto Magalhães, Prãa Pedro Nunes 88, 4099-028 Porto, Portugal and 3 Consulta de Endocrinologia Pediátrica, Hospital de Santa Maria, Av. Prof. Egas Moniz, 1699 Lisboa Codex, Portugal
(Correspondence should be addressed to R Santos; Email: rosario.santos{at}igm.min-saude.pt)
Objective: Defects in the human thyroid peroxidase (TPO) gene are reported to be one of the causes of congenital hypothyroidism (CH) due to a total iodide organification defect. The aim of the present study was to determine the nature and frequency of TPO gene mutations in patients with CH, characterised by elevated TSH levels and orthotopic thyroid gland, identified in the Portuguese National Neonatal Screening Programme.
Subjects and methods: The sample comprised 55 patients, from 53 unrelated families, with follow-up in the endocrinology clinics of the treatment centres of Porto and Lisbon. Mutation screening in the TPO gene (exons 117) was performed by single-strand conformational analysis followed by sequencing of fragments with abnormal migration patterns.
Results: Eight different mutations were detected in 13 patients (seven homozygotes and six compound heterozygotes). Novel mutations included three missense mutations, namely 391T > C (S131P), 1274A > G (N425S) and 2512T > A (C838S), as well as the predictable splice mutation 2748G > A (Q916Q/spl?). The undocumented polymorphism 180-47A > C was also detected.
Conclusion: The results are in accordance with previous observations confirming the genetic heterogeneity of TPO defects. The proportion of patients in which the aetiology was determined justifies the implementation of this molecular testing in our CH patients with dyshormonogenesis.
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