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Novel thyroid specific transcripts identified by SAGE: implication for congenital
hypothyroidism
Moreno Navarro, J.C.
Publication date
2003
Link to publication
Citation for published version (APA):
Moreno Navarro, J. C. (2003). Novel thyroid specific transcripts identified by SAGE:
implication for congenital hypothyroidism.
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CHAPTERR 3
Inactivatingg mutations in the gene for thyroid oxidase 2
(THOX2)) and congenital hypothyroidism.
Joséé C. Moreno, Hennie Bikker. Marlies J. Kempers. A.S. Paul van T rotsenburg. Frankk Baas. Jan J.M. de Vijlder. Thomas Vulsma. Carolyn Ris-Stalpers.
DepartmentDepartment of Pediatric Endocrinology. Emma Children's Hospital. AcademicAcademic Medical Center. University of Amsterdam. The Netherlands.
Cunqb'"-- ta: n v n o ^ y r o : : : ^ - rin-'j THOX2 T ^ a t ' C ^
A b s t r a c t t
Backgroundd Several genetic defects are associated with permanent congenital
hypothyroidism.. Immunologic, environmental, and iatrogenic (but not genetic) factorss are known to induce transient congenital hypothyroidism, which spontaneouslyy resolves within the first months of life. We hypothesized that molecularr defects in the thyroid oxidase system, which is composed of at least two proteins,, might be involved in the pathogenesis of permanent or transient congenital hypothyroidismm in babies with defects in iodide organification, for which the oxidase systemm is required.
Methodss Nine patients were recruited who had idiopathic congenital
hypothyroidismm (one with permanent and eight with transient hypothyroidism) and ann iodide- organification defect and who had been identified by the screening programm for congenital hypothyroidism. The DNA of the patients and their relatives wass analyzed for mutations in the genes for thyroid oxidase 1 (THOX1) and 2 (THOX2). .
Resultss The one patient with permanent and severe thyroid hormone deficiency
andd a complete iodide-organification defect had a homozygous nonsense mutation inn the THOX2 gene that eliminates all functional domains of the protein. Three of the eightt patients with mild transient congenital hypothyroidism and a partial iodide-organificationn defect had heterozygous mutations in the THOX2 gene that prematurelyy truncate the protein, thus abolishing its functional domains.
Conclusionss Biallelic inactivating mutations in the THOX2 gene result in complete
disruptionn of thyroid hormone synthesis and are associated with severe and permanentt congenital hypothyroidism. Monoallelic mutations are associated with milder,, transient hypothyroidism caused by insufficient thyroidal production of hydrogenn peroxide, which prevents the synthesis of sufficient quantities of thyroid hormoness to meet the large requirement for thyroid hormones at the beginning of life. .
KeyKey words Oxidase. THOX1. THOX2. mutations, hydrogen peroxide, transient
Introduction n
Congenita!! hypothyroidism is the most common congenital endocrine disoraer affectingg 1 m every 3000 to 4000 newborns. Neonatal screening programs allow its earlyy detection and treatment, thus preventing the cognitive and motor impairment causedd by lacK of thyroid hormone during the early postnatal phase of brain developmentt [1]. The need for thyroia hormone supplementation can be permanent orr transient '2.3].
Thee cause of permanent congenita1 hypothyroidism of primary origin has been
linkedd to defects in proteins involved in the synthesis of thyroid hormones [4] and to defectss in transcnphon factors involved in the development of the thyroid gland [5-7|.. Overall, these cases represent a small percentage of the population with congenitall hypothyroidism, and the cause of the vast majority of cases remains unknownn [8.9],
Transientt congenital hypothyroidism can be caused by endemic iodine deficiency, exposuree to excess iodine m the De-natal period (e.g from the use of lodmated disinfectanss or contrast agents), or fetal exposure to either maternally derived thyroid-blockingg antibodies or antithyroid drugs taken by pregnant women with thyroidd autoimmune disease [10-13] Congenital thyroid dysfunction can also be a consequencee of premature birth [14.15]. or. in rare cases, of protein-losing nephrosiss [16]. However, in about 20 percent of patients with transient disease, the causee remains elusive [17-20], Sporadic reports have suggested that transient congenita!! hypothyroidism might oe related to mild thyroid dyshormonogenesis [21]. .
Thee generation of hydrogen peroxide is a cr.tical step in the synthesis of thyroid hormoness [22]. Hydrogen peroxide .s used as a substrate by thyroid peroxidase in thee incorporation of iodine into thyroglobuhn. an essential step of thyroid hormonogenesiss known as organ f cation. The thyroid oxidase 1 (THOX1) and 2 (THOX2)) proteins have recently :.)een identified as components of the hydrogen peroxidee generation system of the thyroid [23.24], The level of expression of the THOX22 gene, as determined by serial analysis of gene expression, is at least five timess as high as that of THOX1 [25]. The THOX1 and THOX2 genes encode two veryy similar proteins that are inserted in the apical membrane of the thyroid follicular cell.. The structure of these proteins includes 7 putative transmembrane domains, fourr NADPH-bindung sites and o^e flavme adenine dinucleotide (FAD)-binding site, andd (unlike other human oxidases) two EF-hand motifs (so termed because helixes
EE and F resemble an outstretched index finger and thumb, respectively) that putativelyy control enzymatic act.vity through calcium binding [26],
Mostt inborn errors of thyroid hormone synthesis are caused by defects in iodide organification.. To date, patients with thyroid-organification defects have been shown too harbor mutations in the genes encoding thyroid peroxidase, thyreoglobulin, and pendrinn [27-29], We tested the hypothesis that mutations in the thyroid oxidase systemm are the molecular basis for apparently idiopathic cases of congenital hypothyroidismm with an iodide-organification defect.
Methods s
SelectionSelection of Patients
Patientss with congenital hypothyroidism were selected for genetic screening after writtenn informed consent had been obtained from the parent or guardian The inclusionn criterion was the presence of an iodide-organification defect, as determinedd by a positive intravenous perchlorate test (discharge. 10 percent or moree in the neonatal period. Patients who had iodide-organification defects of knownn cause were excluded. The causes included complete iodide-organification defectss with mutations in the thyroid peroxidase gene [27]: Pendred's syndrome or mutationss in the PDS gene, which encodes the iodide transporter pendrin [30]: and biochemicall indicators of thyroglobulin-synthesis defects or mutations in the thyreoglobulinn gene [31]. Patients who had transient congenital hypothyroidism of knownn cause were also excluded. The causes included maternal thyroid
autoimmunee disease; maternal use of antithyroid drugs during pregnancy, an
excesss or shortage of iodine and premature birth.
EvaluationEvaluation of Clinical Data
Dataa on gestational age. mode of delivery, birth weight and documented use of iodmatedd products were collected from clinical files. In the Dutch screening program forr congenital hypothyroidism, the total thyroxine in a filter-paper blood spot is determined,, normally within the first week of life. When thyroxine values are less thann or equal to -0.8 S.D of the mean value on the standard daily distribution curve, thyrotropinn is measured. When the screening results are abnormal, plasma thyrotropin,, total thyroxine, free thyroxine, total triiodothyronine, thyroxine-binding globulinn and thyroglobulin are determined Urinary excretion of iodine is determined withinn the first three weeks of life [32]. Before the start of thyroxine treatment, when dyshormonogenesiss is suspected, the uptake of iodine-123 by the thyroid is measured,, foliowed by the administration of sodium perchlorate Thyroid hormone therapyy is monitored by periodic determinations of plasma thyrotropin and free thyroxinee levels, and the thyroxine dose is adjusted accordingly. Therapy is stopped
inn patients with suspected transient hypothyroidism when they reach the age of threee years. Four weeks later, thyrotropin, thyroxine, and tniocothyronme are measured,, undergo withdrawal f m n therapy. Four weeKs after withdrawal, thyrotropin.. T4 and T3 are determined All these measurements obtained from the studyy patients were compared with 44 patients with congenital hypothyroidism who hadd a complete lodide-organificaüon defect due to mutations in the thyroid peroxidasee gene.
Perchlorate-DischargePerchlorate-Discharge test
Thee perchlorate challenge was perormed according to a protocol adapted for neonatess [19]. After intravenous administration of 0 9 MBg i25 uCi) [ " d] sodium iodide,, thyroidal uptake of the isotope was monitored every 30 minutes with a gammaa camera and a pinhole collimator. At 120 minutes. 100 mg of sodium perchloratee was given intravenously, and the decrease in radioactivity in the thyroid wass determined at 150 and 180 mmutes. The percent discharge of iodine from the thyroidd gland was calculated as the ratio between the uptake 60 minutes after perchloratee administration and the uptake just before perchlorate administration, multipliedd by 100. A discharge value above 10 percent indicates failure to retain the administeredd radioiodine. usually because of a defect in organification.
IdentificationIdentification of the Genomic Organization of the THOX1 and THOX2 genes
Thee GenBank data base was screened with the THOX1 and THOX2 complementaryy DNA sequences :'AF230495 and AF230496). From three human genomicc clones (contigs) on chromosome 15 (AC009700.4. AC12255.4 and AC051619).. the intran-exon boundaries of the THOX genes were analyzed, and the numberr of coding exons was determined.
DetectionDetection of Mutations
Afterr written informed consent had been obtained, genomic DNA was isolated from thee venous blood of patients and first-degree relatives, together with 100 control subjectss of white, black and Asian origin. The complete coding region of the human THOX11 and THOX2 genes, including intron-exon boundaries, was amplified from genomicc DNA with use of the polymerase chain reaction (PCR) and sense and antisensee primers designed on the basis of the genetic seqiuenr.es. The PCR fragmentss were analyzed on an Agilent 1100-DHPLC system equipped with a Zorbaxx double-stranded DNA temperature-controlled column and a Diode array detectorr [33.34], The oligonucleotide sequences. PCR-amplification process, and conditionss used in chromatography are described in Supplementary Appendix 1
Congenitaa hypothyroidism and THOX2 ^lutcst.rjrs
(availablee with the full text of this article at http://www.nejm.org). Samples showing ann aberrant chromatographic pattern were directly sequenced with fluorescent dideoxynucleotidee primers (Big Dye. Perkin Elmer Applied Biosystems) on an automatedd DNA sequencer (ABI 3100. Perkin Elmer Applied Biosystems).
Thee relatives of the patients and the 100 controls underwent genotyping by heteroduplexx analysis, sequencing or digestion of the respective DNA-amplified PCRR products with appropriate restriction enzymes, according to the specifications off the manufacturers.
Thee sponsors of this study had no involvement in the design of the study, in the collection,, analysis and interpretation of data, or in the writing of the report.
R e s u l t s s
PatternPattern of Congenital Hypothyroidism in Selected Patients.
Fromm an original cohort of 45 patients with severe congenital hypothyroidism at screeningg and a complete lodide-organification defect, 44 patients were excluded becausee of mutations in the thyroid peroxidase gene, leaving 1 patient of this group inn the study (Patient 1 in Table 1). From an original cohort of 15 patients who had mildd hypothyroidism at screening that proved to be transient during follow-up and a partiall iodide-organification defect, 4 were excluded because of iodine intoxication (11 patient), putative thyroglobulin-synthesis defects (2 patients), or Pendred's syndromee (1 patient) Another three of these patients were not available for genetic testing.. Thus, eight patients in this group were studied (Patients 2, 3, and 4 and the fivee patients with a partial organification defect). Table 1 shows the clinical data from thesee patients and their status with respect to mutations in the THOX1 and THOX2 genes. .
Att screening. Patient 1 had thyroxine levels below the limit of detection and very highh thyrotropin levels. Subsequent diagnostic procedures showed a properly locatedd gland with a high uptake of iodine-123 and complete discharge of iodide in thee perchlorate test. This patient requires continued thyroid hormone therapy.
Tablee 1 Thyroid funtion in patients with iodid-organification defects and mutations
inin the TH0X2 gene
r a n g e e P a t i e n tt 1 Patient 2 Patient 3 Patient 4
PIODD TIOD (N=5>> (N=44) S c r e e n i n g g E t i o l o g i c a ll d i a g n o s i s rlefl-- d u'! 'J' " T44 withdrawal A : ; i '' > : _ ; > ;; r.,' ' .. P : „ - ^ - 44 -V P! }} T S '; P:^-.;P:^-.; T''. M o l e c u l a rr d a t a r . MC iy : - , , . , , , r^ C X 22 p r o t o n ' 7 P C w r H H P ; O CC ~ I O C .'.or- t'l-lütJOlhvrrir'i.llt;--p e r o x i d a s ee ' / . i \ : " - o V = -m oo Di.-:c:n < w o o ^ ; i ' - i n : s l " a l o ; ' ii c; u r o ^ o i k o o oo t i u -f i r c i t hh n a : p o s i t i o ' ; -- R.' -> ;.;~,ol L xx 7 rS7 - » "irTv.i .;: />> -^ Pr! T3G G 11 . , ' - ^ ;; ; ; :'HClC--'èltr.'d d '11 £' H 4 T:.ii n g
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\-. .
K A A N A A:: *"
' . k . i a n c o ^^ -- y -- n x i o ee T S H t | -- , rC' r o p -: T 2 c i i ' i ee e * : r e t : o r - " P O t h y - o i r : u ii v a u e i a<e !n e a " . s S D (ii T j , - , ; , - . ; ; .,; c in ^vv . t w o ' - o i . r s a ' t s r ( t i e II aeso- nv.tcir t ( i ' O t f t i r ; - . i ' e 911 p:)s.tii":-i 9 6 5 t a ; ' i ' : ; - i ' e s i h o '2*7'2*7 -> - . o - c l L. I " U a a d . x << i r- -> : : " ' o L n - i d u v i J O riavCongen.taa r y p o i r y r o d i s m and THOX2 n u i a i o n s
Att screening. Patient 2 had mildly decreased thyroxine and elevated thyrotropin levels,, whereas Patients 3 and 4 had thyroxine values in the low-normal range (0.8 andd 1.1 SD below the mean value of the daily distribution curve, respectively) and hyperthyrotropinemia.. Routine determination of thyrotropin in blood spots at thyroxinee levels below -0.8 SD of the mean value of the daily distribution curve allowedd the detection of hyperthyrotropinemia and subsequent referral of Patients 3 andd 4. lodine-123 uptake studies in each case showed a properly located gland with aa partial (40 to 66 percent) discharge of iodide in the perchlorate test. After several adjustmentss in dosage, these three patients were given very low doses of thyroxine (meann 1 3 ug per kilogram of body weight per day) and after they reached the age off three years, therapy was stopped for diagnostic purposes. All of them remained euthyroidd during the follow-up period of 12 months.
Thee same mild and transient phenotype of congenital hypothyroidism was present inn the other five patients with a partial iodide-organification defect in whom no mutationss in the THOX genes were identified. The phenotype of this subgroup clearlyy differed from that of patients who had severe congenital hypothyroidism with completee iodide-organification defects due to mutations in the gene for thyroid peroxidasee (Table 1).
ScreeningScreening for Mutations of the THOX 1 and 2 genes.
Thee open reading frames of the THOX1 and THOX2 genes are divided among 33 exons,, spanning 36 and 22 kb, respectively, on the long arm of chromosome 15. All 333 coding exons for both genes were PCR-amplified from genomic DNA of the patients.. Analysis of PCR products by denaturing high-performance liquid chromatographyy showed multiple aberrant patterns. Most of them were also present inn normal control alleles, and are considered nonfunctional polymorphisms. The sampless corresponding to the aberrant chromatographic patterns of exon 11 (Patientt 1), exon 16 (Patients 2 and 3) and exon 21 (Patient 4) of the THOX2 gene weree directly sequenced, revealing three different single-nucleotide changes and a 4-bpp deletion. Patient 1 was homozygous for the mutation and Patients 2, 3 and 4 weree heterozygous (Fig.1). These changes were absent in 100 control alleles. In Patientt 1. exon 11 of THOX2 had a homozygous substitution of thymine for cytosine att position 1300 (C1300T) that generates a premature termination signal (R434X). Patientt 2 was heterozygous for the C2056T mutation in exon 16 of THOX2: which alsoo generates a premature stop codon instead of the incorporation of a glutamine (Q686X).. Patient 3 was heterozygous for the C2101T nonsense mutation in exon 16 off THOX2. which changes arginine 701 into a premature termination signal (R701X).. Patient 4 had a monoallelic deletion of GTTC at position 2895
(2895-Chapterr .';,
2898del)) in exon 21 of THOX2 that introduces a frame shift generating a termination signall in exon 22 (S965fsX994,-. Southern blotting found no evidence of chromosomall deletions in the THOX genes (data not shown).
Alll four THOX2 mutations should nduce premature stopcodons that delete the predictedd functional hydrogen peroxide-generating domains and are considered inactivatingg mutations (Fig.2).
PedigreePedigree Analysis.
Thee parents of Families 1 and 2 (from Turkey) and Family 3 (from Surinam.) settled inn the Netherlands before the 1980s, and most of their descendants participated in thee Dutch screening program for congenital hypothyroidism. Family 4 has a white Dutchh background. The parents were all born before the screening was instituted. A totall of 17 persons from two generations were available for hormonal and genetic testing.. The levels of thyrotropin, thyroxine, free thyroxine, triiodothyronine, and thyroglobuiinn and the thyroid size were normal in every member of the four families exceptt for the patients (data not shown). The genotypes of the available family memberss was determined by direct sequencing, restriction-site analysis or heteroduplexx analysis (Fig. 3).
Inn Family 1. the index patient (Subject 11-1 in Figure 3). the product of a consanguineouss marriage, was homozygous for the C1300T mutation in THOX2. Herr father (Subject 1-1). mother (Subject I-2) and brother (Subject II-2) were heterozygous,, and had normal thyroid function.
Inn Family 2, the index patient (Subject II-3 <n Fig. 3) and her father (Subject 1-1 ,i were heterozygouss for the C2056T THOX2 mutant allele, whereas the mother (Subject I-2)) was homozygous for the wild-type allele. The patient's older brother (Subject 11-1) didd not carry the mutation and had normal screening values. Subject II-2 was born inn Turkey and was not available for screening.
Inn Family 3. the index patient (Subject II-2 in Fig. 3). her brother (Subject 11-1) and herr mother (Subject I-2) had the THOX2 C2101T mutation. The results of screening off the patient's brother (Subject II-1) were reported to be normal. Retrieval of these resultss after 10 years showed a blood-spot thyroxine value of 12 ug per deciliter (1544 nmol per liter) corresponding to -0.6 SD of the mean value of the daily distributionn curve, just above the cut-off level for thyrotropin determination in the Dutchh screening program.
Congenitall hypothyroidism and THOX2 mutations
Fig.. 1 Mutations in the Thyroid Oxidase 2 Gene (THOX2) in Patients with
PermanentPermanent and Transient Congenital Hypothyroidism. Sequencing chromatograms of
genomicgenomic DNA from control subjects and patients are shown. Arrows indicate the positions of identifiedidentified mutations. Single chromatogram peaks (C1300T) indicate homozygosity at the mutantmutant locus. Two overlapping peaks at the same locus (C2101T. C2056T) denote heterozygousheterozygous mutations. Double overlapping patterns of chromatogram peaks (2895-2898del)2898del) represent heterozygous frame-shift mutations. The C1300T. C2056T and C2101T nucleotidenucleotide changes induce premature stop codons (TGA or TAG) that truncate the correspondingcorresponding proteins. The 4-bp deletion (GTTC) induced by the 2895-2898del mutation causescauses a shift in the reading frame that leads to a stop codon (TGA) after the coding of 29 aberrantaberrant amino acids. (^ p. 178)
Chapterr 3
Thiss borderline blood-spot thyroxine value might have caused a false negative screeningg result. At 10 years of age, Subject 11-1 was euthyroid and performed normallyy at school. His target height was 173.5 cm. and he growing at -2.0 SD of thee mean value on the Dutch standard growth curve, whereas his sister (Subject II-2)) with a target height of 159 cm, was growing at -0.8 SD of the standard curve. Inn Family 4. the index patient (Subject II-2 in Fig. 3) inherited the THOX2 2895-2898dell mutation from her father (Subject 11-1). Her older brother, who had normal screeningg results, did not carry the deletion.
THOX2 2 proteinn 2 -COOH H R434XX S965fsX994 Q686XX R701X O — OO 50 amino acids Transmemoranee domain EF-handd motif FAD-Qii": : NADPH-bindmgg motil Putativee glycosylal Putativee heme-binding site
Fig.. 2 Functional Domains and Mutations of the Thyroid Oxidase 2 (THOX2)
Protein.Protein. Arrows indicate the places where mutant proteins are prematurely truncated. The frame-shiftframe-shift induced by the S965fsX994 mutation codes for 29 aberrant amino acids before truncation.truncation. The relative position of calcium-binding (EF-handj. flavine adenine dinucleotide (FAD)-binding.(FAD)-binding. and NADPH-binding motifs are indicated. (> - p. 179)
Congenitall hypothyroidism and THOX2 mutations Familyy 1 i i Gene e Mutation n Detection n II ! II I 11.2 THOX2 2 C1300T T DdelDdel RFLP
Familyy 2 Family 3 Familyy 4
. .
ii : ii i ii ; i : THOX2 2 C2056T T AvailAvail RFLP THOX2 2 C2101T T DdelDdel RFLP TH0X2 2 2895-2898del l Heteroduplex Heteroduplex Indexx patientPermanentt congenital hypothyroidism and TIOD Transientt congenital hypothyroidism and PIOD T44 screening result: -0.6 S.D.
Fig.. 3 Segregation Analysis of Mutations in the Thyroid Oxidase 2 Gene (THOX2) in
ThreeThree Families with Permanent or Transient Congenital Hypothyroidism. Squares
indicateindicate male family members, and circles female family members. Arrows indicate index patients,patients, the black symbol a patient with permanent congenital hypothyroidism and a completecomplete iodide-organification defect, the grey symbols patients with transient congenital hypothyroidismhypothyroidism and partial iodide-organification defects, and the stippled symbol a patient withwith a thyroxine-screening result 0.6 SD below the reference value. Gels show
restriction-fragment-lengthfragment-length polymorphism (RFLP) and heteroduplex analyses of mutations. Polymerase-chain-reactionchain-reaction (PCR) fragments were stained with ethidium bromide. Fragments correspondingcorresponding to the mutant alleles are indicated by asterisks. The THOX2 C1300T and C2101TC2101T mutations introduce a Dde I site, and an Ava II site is destroyed by the C2056T mutation.mutation. The 2895-2899del mutation cannot be distinguished by restriction-site analysis, but inin this case the presence of the mutated allele results in a heteroduplex PCR fragment with aberrantaberrant running pattern on agarose gel.
O^pte-- 7;
Discussion n
Thee generation of hydrogen peroxide is an essential step ;n the synthesis of thyroid hormones.. Over the past three decades, a few cases of thyroidal hydrogen peroxide deficiencyy have been described, but the molecular basis of these defects has not beenn investigated [39-41],
Wee studied the genomic organization and screened the THOX1 and THOX2 genes forr mutations in patients with congenital hypothyroidism and lodide-organification defects.. Mutations in the THOX2 ge^e were present in one patient with a complete iodide-organificationn defect and permanent congenital hypothyroidism and in three off eight patients with partial iodide-organification defects and transient congenital hypothyroidism.. All mutations resulted in premature stop codons that delete the NADPH-- and FAD-binding sites of the 1HOX2 protein. Functional studies of g p 9 1p h ü X.. a protein of the phagocyte oxidase system that is homologous with the THOXX proteins, show that truncation of these sites leads to complete loss of activity [42], ,
Thee patient with severe and permanent congenital hypothyroidism w;as
homozygouss for a THOX2 inactivating mutation. This finding proves that abolishing functionall THOX2 protein completely blocks thyroid hormone synthesis.
Thee three patients with a milder and transient form of the disease were heterozygouss for three other inactivating mutations, suggesting that insufficiency of thee THOX2 protein within the thyroid oxidase complex was the underlying mechanismm of disease. However, the neonatal euthyroid profile of Subject II-2 in Familyy 1. who was heterozygous for the C1300T mutation, might indicate the existencee of dominant negative properties in mutant proteins 2. 3. and 4 that are not presentt in mutant protein 1. In contrast to mutant 1. mutants 2. 3. and 4 retain the hydrophobicc stretch of the first transmembrane domain of the THOX2 protein, which mightt allow the insertion of the protein in the membrane and aberrant interactions withh other components of the oxidase system [43], It is tempting to speculate that thesee putative other components are involved in the molecular basis of the transient congenitall hypothyroidism of the patients in our study who did not have THOX1 nor THOX22 mutations.
Partiall insufficiency of the THOX2 protein, resulting in diminished hydrogen peroxidee production, is present only during trie first weeks or months of postnatal life,, when the requirement for thyroid hormones is large. On the basis of evidence thatt transient congenital hypothyroidism and hyperthyrotropinemia are associated withh impaired intellectual development in children [44]. we advise treatment of these patientss as soon as possible after birth, as well as thyroid-function tests in newborn
Congenita,, hvpntryroicisr- a~d THOX2 r u ' a t i o n s
siblingss of children with transient congenital hypothyroidism. Furthermore, it is importantt to follow these patients for subclinical or overt hypothyroidism, goiter, or bothh in adolescence and adulthood, especially during pregnancy, when the need for thyroxinee increases. If the expression of this genetic disorder recurs during pregnancy,, the neurologic development of the offspring can be hampered [45,46]. Inn conclusion, biallelic and monoallelic inactivating mutations in the THOX2 gene aree associated with permanent and transient congenital hypothyroidism, respectively.. These findings prove that THOX2 protein is an essential component of thee thyroidal system of hydrogen peroxide generation. Furthermore, they represent too our knowledge the first demonstration that transient congenital hypothyroidism cann be genetically determined and show that thyroid dyshormonogenesis is involvedd in the transient form of congenital hypothyroidism.
Acknowledgements s
Wee are indebted to patients (and to their parents) for their collaboration, to Janine dee Randamie for her assistance in DNA diagnostics, to Brenda Wiedijk for assistancee in the collection of data, to Dr. B. Bakker, Dr. P. Harmsen and Dr. R. van Andell for clinical follow-up of some patients, and to Professor Dirk Roos for critical readingg of the manuscript.
Supportedd by an ESPE (European Society for Pediatric Endocrinology) Research Fellowship,, sponsored by Novo Nordisk A/S. (to J.CM.), and a grant from the Dr. Ludgardinee Bouwman foundation (to J.J.M.V.).
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