Two Distinct Compound Heterozygous Constellations (R277X/IVS34–1G>C and R277X/R1511X) in the Thyroglobulin (TG) Gene in Affected Individuals of a Brazilian Kindred with Congenital Goiter and Defective TG Synthesis

Abstract

In this study, we have extended our initial molecular studies of a nonconsanguineous family with two affected siblings and one of their nephews with congenital goiter, hypothyroidism, and marked impairment of thyroglobulin synthesis. Genomic DNA sequencing revealed that the index patient (affected nephew) was heterozygous for a single base change of a cytosine to a thymine at nucleotide 886 in exon 7 (886C>T, mother's mutation) in one allele and for a novel guanine to cytosine transversion at position -1 of the splice acceptor site in intron 34 (IVS34-1G>C, father's mutation) in the other allele. The two affected siblings inherited the 886C>T mutation from their mother and a previously reported cytosine to thymine transition at nucleotide 4588 in exon 22 from their father (4588C>T). The 886C>T and 4588C>T substitutions resulted in premature stop codons at amino acids 277 (R277X) and 1511 (R1511X), respectively. In vitro transcription analysis showed that the exon 35 is skipped entirely when the IVS34-1G>C mutation is present, whereas the wild-type allele is correctly spliced. SSCP (exon 7 and 35) and restriction analysis (exon 22) using Taq I indicated that the two affected siblings, the affected nephew, his mother, and his unaffected brother were all heterozygous for the R277X mutation. The two affected siblings, their father, and three unaffected siblings were all heterozygous for the R1511X mutation, whereas the affected nephew and his father were heterozygous for the IVS34-1G>C mutation. Moreover, in this kindred, we have characterized polymorphisms (insertion/deletion, microsatellite, and single nucleotide polymorphism) located within introns 18 and 29 and exon 44 that are associated with the described mutations. Haplotype analysis with these polymorphic markers in two unrelated Brazilian families (present family studied and previously reported family) harboring the R277X mutation suggests a founder effect for the R277X mutation. In conclusion, the affected individuals of this family are either compound heterozygous for R277X/IVS34-1G>C or R277X/R1511X. This observation further supports that thyroglobulin gene mutations display significant intraallelic heterogeneity.

Recurrence of the p.R277X/p.R1511X compound heterozygous mutation in the thyroglobulin gene in unrelated families with congenital goiter and hypothyroidism: haplotype analysis using intragenic thyroglobulin polymorphisms

“…Mutations in the human TG gene are associated with congenital goiter (Ieiri et al 1991, Targovnik et al 1993, 1995, Medeiros-Neto et al 1996, van de Graaf et al 1999, Hishinuma et al 1999, Caron et al 2003, Gutnisky et al 2004, Mendive et al 2005, Rivolta et al 2005, Alzahrani et al 2006, Kitanaka et al 2006 or endemic (Pérez-Centeno et al 1996) and non-endemic simple goiter (Corral et al 1993, González-Sarmiento et al 2001. Thirty-five inactivating mutations have been identified and characterized in the human TG gene: 20 missense mutations (p.C175G, p.Q310P, p.Q851H, p.S971I, p.R989C, p.P993L, p.C1058R, p.C1245R, p.S1447N, p.C1588F, p.C1878Y, p.I1912V, p.C1977S, p.C1987Y, p.C2135Y, p.R2223H, p.G2300D, p.R2317Q, p.G2355V, p.G2356R), 5 nonsense mutations (p.R277X, p.Q692X, p.W1418X, p.R1511X, p.Q2638X), 8 splice site mutations (g.IVS3-3COG, g.IVS5C1GOA, g.IVS10-1GOA, g.IVS24C1GOC, g.IVS30C1GOT, g.IVS30C lGOA, g.IVS34-1GOC, g.IVS45C2TOA) and 2 single nucleotide deletions (p.G362fsX382, p.D1494fsX1547) (Ieiri et al 1991, Corral et al 1993, Targovnik et al 1993, 1995, Medeiros-Neto et al 1996, Pérez-Centeno et al 1996, van de Graaf et al 1999, Hishinuma et al 1999, González-Sarmiento et al 2001, Caron et al 2003, Gutnisky et al 2004, Mendive et al 2005, Rivolta et al 2005, Alzahrani et al 2006, Kitanaka et al 2006. Rivolta et al (2005) reported that the p.R277X mutation is the most frequently identified TG mutation in south American population and haplotype studies suggest that a mutational hot spot could explain the recurrence of...…”

“…We have previously identified a p.R277X/p.R1511X compound heterozygous TG mutation in two members of a Brazilian family with a complex history of congenital goiter (Targovnik et al 1993, Gutnisky et al 2004, Mendive et al 2005.…”

A novel compound heterozygous mutation in the thyroglobulin gene resulting in congenital goitrous hypothyroidism with high serum triiodothyronine levels

“…Some patients with thyroglobulin gene mutations have been reported with normal serum T3 levels as well as low T4 levels (Ieiri et al 1991;Targovnik et al 1993;van de Graaf et al 1999;Gutnisky et al 2004). This condition may be one of the characteristics of thyroglobulin abnormality.…”

“…The prevalence of patients with thyroglobulin defects is 1:40,000-100,000 newborns. However, due to the difficulty of analyzing large genes, only nine different mutations leading to congenital goiter and hypothyroidism have thus far been identified in the human thyroglobulin gene (Ieiri et al 1991;Targovnik et al 1993Targovnik et al , 1995van de Graaf et al 1999;Hishinuma et al 1999;Caron et al 2003;Gutnisky et al 2004).…”

Congenital hypothyroidism

“…Mutations in the dual oxidase maturation factor (DUOXA2) gene also lead to deficient iodide organification through similar mechanisms and can cause partial iodide organification defects [49]. Other, rare causes of dyshormonogenesis include defects in sodium/iodide transport, resulting from a mutation in the gene encoding the sodium-iodide symporter [50], and defective thyroglobulin action, resulting from a mutation in the gene encoding thyroglobulin [51]. A defect in the enzyme iodotyrosine deiodinase which aids in the peripheral conversion of T4 to T3 has been shown in hypothyroid individuals.…”