Hereditary congenital goitre with thyroglobulin deficiency causing hypothyroidism

Protein Aggregation in the ER: Calm behind the Storm

As one of the largest organelles in eukaryotic cells, the endoplasmic reticulum (ER) plays a vital role in the synthesis, folding, and assembly of secretory and membrane proteins. To maintain its homeostasis, the ER is equipped with an elaborate network of protein folding chaperones and multiple quality control pathways whose cooperative actions safeguard the fidelity of protein biogenesis. However, due to genetic abnormalities, the error-prone nature of protein folding and assembly, and/or defects or limited capacities of the protein quality control systems, nascent proteins may become misfolded and fail to exit the ER. If not cleared efficiently, the progressive accumulation of misfolded proteins within the ER may result in the formation of toxic protein aggregates, leading to the so-called “ER storage diseases”. In this review, we first summarize our current understanding of the protein folding and quality control networks in the ER, including chaperones, unfolded protein response (UPR), ER-associated protein degradation (ERAD), and ER-selective autophagy (ER-phagy). We then survey recent research progress on a few ER storage diseases, with a focus on the role of ER quality control in the disease etiology, followed by a discussion on outstanding questions and emerging concepts in the field.

Six new mutations of the thyroglobulin gene discovered in taiwanese children presenting with thyroid dyshormonogenesis

BACKGROUND

Thyroglobulin (TG) defect is a rare cause of congenital hypothyroidism. Although only 44 mutations of the human TG gene have been identified, we have suspected a TG defect in 38% of Taiwan Chinese children/adolescents presenting with moderate or severe thyroidal dyshormonogenesis.

STUDY OBJECTIVE

The aim of the study is to report the discovery of new TG gene mutations and associated clinical manifestations of the defective TG protein.

PATIENTS AND RESULTS

In seven patients from six families, we detected six new TG gene mutations, including c.1348delT, p.R432X (c.1351C>T), g.IVS3 + 2T>G, c.1712delT, p.Q1765X (c.5350C>T), and c.6047delA. The c.1348delT and p.R432X mutations were the most common, detected in 33 and 25%, respectively, of alleles studied. Haplotype analysis suggested that the c.1348delT and g.IVS3 + 2T>G mutations are due to founder effects, whereas p.R432X is probably due to independently recurrent de novo mutations. mRNA transcript of the g.IVS3 + 2T>G mutant, detected in whole blood by reverse transcription-nested PCR, showed skipping of exon 3 (98-bp deletion) and a frameshift, with a terminal signal after 17 altered amino acid residues.

CONCLUSIONS

TG defects have an important role in severe thyroidal dyshormonogenesis (pretreatment, or after a 3-wk T(4) withdrawal, plasma T(4) < or = 30 nmol/liter) in Taiwanese. Its genetic characteristics are markedly different from those described in other populations presenting with mutations of the TG gene.

Clinical and morphologic findings of familial goiter in bongo antelope (Tragelaphus eurycerus)

Inherited defects of thyroglobulin synthesis resulting in congenital goiter are well described in certain breeds of domestic ungulates and in human beings. Goiter associated with synthesis of an abnormal thyroglobulin and the presence of thyroidal albumin was identified in five closely related bongo antelopes (Tragelaphus eurycerus). The goiter had an adult onset, and the affected bongos appeared to remain euthyroid with normal serum T3 and T4 values, normal serum cholesterol concentrations, and nonelevated concentrations of circulating thyroid stimulating hormone (TSH). Goitrous bongos had significant reproductive difficulties, including reduced cyclic activity and prolonged gestations, but were otherwise normal. Over the course of the disease, the thyroid glands greatly enlarged (up to 10 x 20 cm) and became polycystic. Microscopically, there was an admixture of giant colloid-filled follicles and follicles of normal size lined with variable follicular epithelium ranging from squamoid to mildly to moderately hyperplastic. The pathogenesis of goiter in the bongo may reflect a mixture of genetic predisposition coupled with environmental factors, including a period of exposure to a goitrogen.

Congenital euthyroid goitre with impaired thyroglobulin transport

A case of congenital goitre with defective thyroglobulin (Tg) synthesis was studied from the clinical, biochemical and morphological perspectives. The patient, 5.5-year-old boy, who was clinically euthyroid, showed a positive perchlorate discharge test (37.2%). However, the iodination system seemed to be normal since radioiodine uptake into the thyroid was very high, and inspection of the H2O2-generating system using thyroid slices and an assay for peroxidase activity in microsomes showed no abnormalities. On the other hand, virtually no Tg was detected in the serum, and the amount of Tg in thyroid tissue, estimated with gel electrophoresis, was below 10% of the normal value, the quality of Tg being unchanged. Morphological observations demonstrated the presence of Tg in the markedly distended rough endoplasmic reticulum of the cytoplasm of follicular cells and a lack of Tg in the colloid of the follicular lumen. These results suggest that the thyroid is defective in Tg synthesis, probably associated with impaired transport of Tg from the cells to the lumen.

Low-molecular-weight iodoproteins in the congenital goiters of cog/cog mice

Previously we described sedimentation and immunologic abnormalities of thyroglobulin (Tg) in a strain of mice with inherited congenital goiter and hypothyroidism (cog/cog). The goals of the present study were to determine the extent to which thyroid gland stimulation by TSH accounts for the abnormal properties of cog/cog Tg and to characterize further the abnormally small iodoproteins found in cog/cog mice. Cog/cog and control +/cog and BALB/c mice were fed with either normal or thyroid-hormone-containing diets and were injected with Na125I. Sucrose density gradient centrifugation of labeled thyroid extracts from cog/cog mice on normal diet showed that 82% of the iodine was in iodoproteins smaller than Tg, with sedimentation rates of 3-8S. No 12S and 19S peaks, characteristic of normal Tg, were present, but distinct and stable 12S and 19S peaks emerged after recentrifugation of the 12S and 19S areas. In contrast, in cog/cog mice treated with T4, a smaller (55%) amount of 3-8S iodoproteins and distinct 12S and 19S peaks were present. In both groups of mice, the labeled 3-8S iodoproteins were composed of three fractions: 15% precipitated by antirat Tg serum, 38% precipitated by antimouse albumin serum, and 47% not precipitated by either serum. The 3-8S iodoproteins contained labeled MIT and DIT and no T4. On sodium dodecyl sulfate polyacrylamide gel electrophoresis the 3-8S iodoprotein fraction that reacted with anti-Tg serum contained a distinct electrophoretic band at 49K. The 3-8S nonreactive iodoproteins resolved into several bands of lower molecular weight. We conclude that the 3-8S iodoproteins in cog/cog mice are heterogeneous and that TSH stimulation contributes to the production of these low-molecular-weight iodoproteins.