Clinical and epidemiological characteristics of thyroid hemiagenesis: ultrasound screening in patients with thyroid disease and normal population

Thyroid hemiagenesis is a rare form of thyroid dysgenesis, in which one thyroid lobe fails to develop. The true prevalence of this rare abnormality is about 0.05-0.2% in normal population. We aimed to determine prevalence of thyroid hemiagenesis in patients with various thyroid disorders and a normal population in a mild to moderate iodine-deficient area. The clinical and thyroid ultrasonography records of 4,833 patients who presented with various thyroid disorders were reviewed. In addition, ultrasonographic data of two large surveys carried out for the community screening of iodine status of children (n = 4,772) and thyroid disorders of adult subjects (n = 2,935) were analyzed. In patients with thyroid disorders, we found 12 cases with thyroid hemiagenesis (0.25%). Thyroid hemiagenesis was due to the agenesis of the left lobe in all cases. The underlying thyroid diseases were Hashimoto's thyroiditis (n = 4), euthyroid multinodular goiter (n = 4), and toxic adenoma (n = 1). Three subjects have no underlying thyroid disease. In ultrasonography screening of normal population, altogether, the absence of the left lobe was detected in only two cases, indicating a true prevalence of thyroid hemiagenesis of 0.025%. None of the reviewed patients had thyroid dysfunction. Our community-based data is in accordance with previous studies in terms of prevalence and male-to-female ratio.

Screening for mutations in transcription factors in a Czech cohort of 170 patients with congenital and early-onset hypothyroidism: identification of a novel PAX8 mutation in dominantly inherited early-onset non-autoimmune hypothyroidism

OBJECTIVE

Mutations in NKX2.1, NKX2.5, FOXE1 and PAX8 genes, encoding for transcription factors involved in the development of the thyroid gland, have been identified in a minority of patients with syndromic and non-syndromic congenital hypothyroidism (CH).

DESIGN

In a phenotype-selected cohort of 170 Czech paediatric and adolescent patients with non-goitre CH, including thyroid dysgenesis, or non-goitre early-onset hypothyroidism, PAX8, NKX2.1, NKX2.5, FOXE1 and HHEX genes were analysed for mutations.

METHODS

NKX2.1, NKX2.5, FOXE1 and HHEX genes were directly sequenced in patients with syndromic CH. PAX8 mutational screening was performed in all 170 patients by single-stranded conformation polymorphism, followed by direct sequencing of samples with abnormal findings. The R52P PAX8 mutation was functionally characterized by DNA binding studies.

RESULTS

We identified a novel PAX8 mutation R52P, dominantly inherited in a three-generation pedigree and leading to non-congenital, early-onset, non-goitre, non-autoimmune hypothyroidism with gradual postnatal regression of the thyroid size and function. The R52P PAX8 mutation results in the substitution of a highly conserved residue of the DNA-binding domain with a loss-of-function effect.

CONCLUSIONS

The very low frequency of genetic defects in a population-based cohort of children affected by non-goitre congenital and early-onset hypothyroidism, even in a phenotype-focussed screening study, suggests the pathogenetic role of either non-classic genetic mechanisms or the involvement of genes unknown so far. Identification of a novel PAX8 mutation in a particular variant of non-congenital early-onset hypothyroidism indicates a key function of PAX8 in the postnatal growth and functional maintenance of the thyroid gland.

Clinical evaluation of isolated nonvisualized fetal gallbladder

OBJECTIVE

Isolated nonvisualized fetal gallbladder (INVFGB) is relatively rare. In most cases, the gallbladder will eventually be detected. In some cases however, INVFGB may be associated with serious abnormalities, cystic fibrosis (CF), aneuploidy, and agenesis of the gall bladder. We describe a clinical evaluation of prenatally diagnosed INVFGB.

METHODS

Cases of nonvisualized gallbladder were first evaluated by serial scans. Cases with no additional malformations were designated as INVFGB, and were further evaluated by mutation analysis for CF, and amniocentesis for karyotype and microvillar membrane enzymes (MME).

RESULTS

A total of 22 cases of nonvisualized gallbladder were detected. Of these, 2 had additional malformations, and 3 were excluded because of incomplete evaluation. Of the remaining 17 cases, 3 (17.6%) had adverse outcomes: 1 case of CF, 1 case of 47,XXX, and 1 case of multiple congenital anomalies detected only postnatally. Abnormal levels of MMEs were detected in 3 cases, 1 of which was diagnosed with CF. In 2 cases, the gallbladder was not detected even after birth, but development is normal.

CONCLUSION

Evaluation of INVFGB should include genetic counselling, amniocentesis for karyotype and MME analysis, CFTR mutation analysis and repeated ultrasound scans.

Thyroid imaging in children

Ultrasonography (US) and radionuclide thyroid scanning are the imaging modalities of choice in the evaluation of the thyroid gland in children. The main normal US patterns of the thyroid gland are reviewed. In early infancy, thyroid imaging is usually performed in the context of congenital hypothyroidism (CH). The aetiological diagnosis of CH is usually based on the combined use of US and radionuclide thyroid scanning. A detailed description of thyroid abnormalities observed in CH is given. Thyroid dysgenesis includes athyreosis, 'empty' thyroid area with ectopic thyroid tissue and thyroid hypoplasia (global hypoplasia and thyroid hemiagenesis). Mild thyroid developmental anomalies (pyramidal lobe, thyroglossal duct cysts, thyroid hemiagenesis) may be observed in euthyroid patients or among first-degree relatives of a CH population with thyroid dysgenesis. A normally located gland (goitre, normal-sized thyroid gland or hypoplastic thyroid gland) may also be observed in patients with CH. The main patterns observed in chronic and acute thyroiditis, in hyperthyroidism and thyroid tumours are described. Moreover, fetuses and neonates born to mothers with Graves' disease are at risk of thyroid dysfunction and goitre due to hypothyroidism in relation to excessive maternal treatment or to maternal hyperthyroidism which may be observed with fetal US.