Mireille Castanet

FIVE NEW TTF1/NKX2.1 MUTATIONS IN BRAIN-LUNG-THYROID SYNDROME: RESCUE BY PAX8 SYNERGISM IN ONE CASE

Thyroid transcription factor 1 (NKX2-1/TITF1) mutations cause brain-lung-thyroid syndrome, characterized by congenital hypothyroidism (CH), infant respiratory distress syndrome (IRDS) and benign hereditary chorea (BHC). The objectives of the present study were (i) detection of NKX2-1 mutations in patients with CH associated with pneumopathy and/or BHC, (ii) functional analysis of new mutations in vitro and (iii) description of the phenotypic spectrum of brain-lung-thyroid syndrome. We identified three new heterozygous missense mutations (L176V, P202L, Q210P), a splice site mutation (376-2A-->G), and one deletion of NKX2-1 at 14q13. Functional analysis of the three missense mutations revealed loss of transactivation capacity on the human thyroglobulin enhancer/promoter. Interestingly, we showed that deficient transcriptional activity of NKX2-1-P202L was completely rescued by cotransfected PAX8-WT, whereas the synergistic effect was abolished by L176V and Q210P. The clinical spectrum of 6 own and 40 published patients with NKX2-1 mutations ranged from the complete triad of brain-lung-thyroid syndrome (50%), brain and thyroid disease (30%), to isolated BHC (13%). Thyroid morphology was normal (55%) and compensated hypothyroidism occurred in 61%. Lung disease occurred in 54% of patients (IRDS at term 76%; recurrent pulmonary infections 24%). On follow-up, 20% developed severe chronic interstitial lung disease, and 16% died. In conclusion, we describe five new NKX2.1 mutations with, for the first time, complete rescue by PAX8 of the deficient transactivating capacity in one case. Additionally, our review shows that the majority of affected patients display neurological and/or thyroidal problems and that, although less frequent, lung disease is responsible for a considerable mortality.

NKX2-1 Mutations Leading to Surfactant Protein Promoter Dysregulation Cause Interstitial Lung Disease in "Brain-Lung-Thyroid Syndrome''

NKX2‐1 (NK2 homeobox 1) is a critical regulator of transcription for the surfactant protein (SP)‐B and ‐C genes (SFTPB and SFTPC, respectively). We identified and functionally characterized two new de novo NKX2‐1 mutations c.493C>T (p.R165W) and c.786_787del2 (p.L263fs) in infants with closely similar severe interstitial lung disease (ILD), hypotonia, and congenital hypothyroidism. Functional analyses using A549 and HeLa cells revealed that NKX2‐1‐p.L263fs induced neither SFTPB nor SFTPC promoter activation and had a dominant negative effect on wild‐type (WT) NKX2‐1. In contrast,NKX2‐1‐p.R165W activated SFTPC, to a significantly greater extent than did WTNKX2‐1,whileSFTPB activation was only significantly reduced in HeLa cells. In accordance with our in vitro data, we found decreased amounts of SP‐B and SP‐C by western blot in bronchoalveolar lavage fluid (patient with p.L263fs) and features of altered surfactant protein metabolism on lung histology (patient with NKX2‐1‐p.R165W). In conclusion, ILD in patients with NKX2‐1 mutations was associated with altered surfactant protein metabolism, and both gain and loss of function of the mutated NKX2‐1 genes on surfactant protein promoters were associated with ILD in “Brain‐Lung‐Thyroid syndrome”.

Familial Forms of Thyroid Dysgenesis among Infants with Congenital Hypothyroidism

To the Editor: Thyroid dysgenesis (thyroid aplasia or an ectopic thyroid gland) is responsible for 85 percent of cases of congenital hypothyroidism. The pathogenesis of thyroid dysgenesis is not kn...

Experience with Intraamniotic Thyroxine Treatment in Nonimmune Fetal Goitrous Hypothyroidism in 12 Cases

CONTEXT Nonimmune fetal goitrous hypothyroidism is a rare condition that can induce obstetrical and/or neonatal complications and neurodevelopmental impairments such as those still seen in some patients with congenital hypothyroidism. Prenatal treatment to prevent these adverse outcomes is appealing, but experience is limited and the risk to benefit ratio controversial. OBJECTIVE The objective of the study was to evaluate the feasibility, safety, and effectiveness of intrauterine l-thyroxine treatment in a large cohort with nonimmune fetal goitrous hypothyroidism. DESIGN This was a retrospective study of 12 prenatally treated fetuses diagnosed between 1991 and 2005 in France. METHODS During pregnancy, goiter size and thyroid hormone levels were compared before and after prenatal treatment. At birth, clinical, laboratory, and ultrasound data were evaluated. RESULTS Prenatal treatment varied widely in terms of l-thyroxine dosage (200-800 microg/injection), number of injections (one to six), and frequency (every 1-4 wk). No adverse events were recorded. During pregnancy, thyroid size decreased in eight of nine cases and amniotic-fluid TSH levels decreased in the six investigated cases, returning to normal in four. However, at birth, all babies had hypothyroidism, indicating that intraamniotic TSH levels did not reliably reflect fetal thyroid function. CONCLUSION Our data confirm the feasibility and safety of intraamniotic l-thyroxine treatment for nonimmune fetal goitrous hypothyroidism. Although goiter size reduction is usually obtained, thyroid hormone status remains deficient at birth. Amniocentesis seems inadequate for monitoring fetal thyroid function. Further studies are needed to determine the optimal management of this disorder.

Update on Cystic Fibrosis-Related Bone Disease: A Special Focus on Children

A high prevalence of low bone mineralization is documented in adult patients with cystic fibrosis (CF). Osteopenia is present in up to 85% of adult patients and osteoporosis in 10% to 34%. In children, study results are discordant probably because of comparisons to different control populations and corrections for bone size in growing children. Malnutrition, inflammation, vitamin D and vitamin K deficiency, altered sex hormone production, glucocorticoid therapy, and physical inactivity are well known risk factors for poor bone health. Puberty is a critical period for bone mineralization and requires a careful follow-up to achieve optimal bone peak mass. Strategies for optimizing bone health, such as monitoring bone mineral density (BMD) and providing preventive care are necessary from childhood through adolescence to minimize CF-related bone disease in adult CF patients.

Linkage and mutational analysis of familial thyroid dysgenesis demonstrate genetic heterogeneity implicating novel genes

The pathophysiology of thyroid dysgenesis (TD) is not elucidated yet in the majority of cases. The unexpected familial clustering of congenital hypothyroidism due to TD suggests a genetically determined disorder. Four genes have been hitherto involved in thyroid development, including migration and growth. Three of these encode transcription factors (the thyroid transcription factors 1 and 2 (TTF1 or NKX2.1 and TTF2 or FOXE1) and PAX8) while the other encodes the thyrotropin hormone receptor (TSHR). Some mutations have been reported in patients affected by thyroid defects, which supports the relevance of these four genes in TD. However, their involvement in the general TD population remains questionable. Therefore, to document their involvement, we performed a linkage analysis followed by mutational analysis in 19 multiplex TD families. The LOD score results failed to prove linkage between any of the four genes and the TD phenotype, whatever the postulated mode of inheritance. Manual extended haplotypes showed allele sharing among affected individuals of at least one of these four genes in the majority of families. Nevertheless, mutational analysis did not identify mutations in these cases, arguing in favor of identity by descent and not identity by state. Furthermore, as a main result of the present study, extended haplotypes confirmed by mutational analysis showed that the four genes were excluded in five out of the 19 investigated families, demonstrating the relevance of other genes. In conclusion, the present study demonstrates genetic heterogeneity in the TD disorder and suggests the involvement of novel genes.

Primary Hyperparathyroidism in Neonates and Children

Objectives: Primary hyperparathyroidism (HP1) in childhood is thought to be extremely rare. Its exact incidence remains unknown, as do the characteristics of HP1. A retrospective st

Thyroid Hemiagenesis Is a Rare Variant of Thyroid Dysgenesis with a Familial Component but without Pax8 Mutations in a Cohort of 22 Cases

Thyroid hemiagenesis is a rare form of thyroid dysgenesis of which some familial cases have been reported, including one associated with a heterozygous mutation in the Pax8 gene. However, the physiopathology remains not well known. The objectives of this study were 1) to describe the clinical features, 2) to look for familial clustering, and 3) to search for Pax8 mutations in a relatively large cohort of affected patients. A family history of thyroid dysgenesis was found in nine patients (40%), whose affected relatives had ectopic thyroid (n = 4), athyreosis (n = 1), thyroid hemiagenesis (n = 2), or thyroglossal duct cysts (n = 2). Screening for Pax8 mutations identified abnormal migration profiles by SSCP analysis in 3 patients, but direct sequencing did not show coding region mutations in any of the 22 patients. In conclusion, this study provides the first evidence that thyroid hemiagenesis can occur as a familial disorder associated with any form of thyroid dysgenesis. This finding supports both a common underlying mechanism to the various abnormalities in thyroid development and a role for genetic factors; however, our results from Pax8 analysis suggest that this gene may not be a key factor.

Molecular Mechanisms of Thyroid Dysgenesis

Thyroid dysgenesis (TD) is the most prevalent form of congenital hypothyroidism. Ttf-1, Ttf-2, Pax8 and the Tshr are expressed at early stages of thyroid development and are implicated in thyroid ontogeny. Mutations in these genes have been found in some cases of TD. The prevalence of familial forms of TD is significantly higher than expected if the disease was only sporadic, allowing to postulate a genetic basis of the disease. Linkage analysis and mutational screening of the four above-mentioned genes in familial forms of TD showed their exclusion as contributors to the disease in some families, implicating genetic heterogeneity and involving other genetic mechanisms. Strategies to uncover new genes involved in TD are therefore needed. We underscore differences in the temporal expression patterns during the human thyroid development with those in animal models. Further, the extrathyroid expression of these genes during human development enables to define the gene-specific malformations that may be present in patients bearing mutations. The data gathered on molecular thyroid development enable precise genetic counselling of affected families. By increasing our knowledge of thyroid development, we hope to uncover new perspectives of genetic screening and eventually of early in utero treatment.

Clinical Description of Infants with Congenital Hypothyroidism and Iodide Organification Defects

Aims: To describe the phenotype of a large group of children with congenital hypothyroidism (CH) and iodide organification defect (IOD), suspected based on normal thyroid position and abnormal perchlorate discharge test, as first step of a project evaluating correlations between phenotypes and genotypes. Methods: 71 children born in Paris between 1980 and 2006 were included. Two groups were defined according to perchlorate discharge: total IOD (TIOD) when the release was above 90% and partial IOD (PIOD) between 10 and 90%. Comparisons between groups were performed using SPSS 14.0 for Windows. Results: The incidence of IOD over the 2003–2006 period was 1:20,660. Of the 71 children, 61 had PIOD and 10 TIOD. Compared to PIOD, TIOD was characterized by greater clinical severity. A wide spectrum of clinical features was seen in the PIOD group. Evolution showed transient hypothyroidism in 10/61 patients with PIOD and 1/10 TIOD patients. Conclusions: Severe presentation in the majority of TIOD patients suggests dysfunction of a key iodide-organification enzyme. In contrast, the variety of clinical features in PIOD group suggests that diverse mechanisms may lead to PIOD, such as delayed or reduced activity of enzymes involved in hormonogenesis or defects in iodine storage and release.