Alterations of neonatal thyroid function

Recent progress has been made in understanding the pathogenesis of neonatal thyroid disorders. Autosomal recessive inheritance of mutations of the thyroid peroxidase and thyroglobulin genes has been described in some patients with congenital hypothyroidism (CH) and a family history of CH. Autosomal recessive inheritance of mutations of the thyrotrophin (TSH) receptor gene has also been reported in patients with CH and thyroid hypoplasia, and autosomal dominant mutations of the PAX8 gene have been described in patients with different forms of thyroid dysgenesis. These discoveries are important for patients with CH diagnosed by neonatal screening, as these patients will have normal fertility. The molecular genetic analysis of mutations of the TSH gene in patients with familial and sporadic cases of isolated central CH, who are missed by TSH screening programmes, now enables rapid diagnosis and appropriate therapy in the neonate. In newborn infants with severe non-autoimmune hyperthyroidism, autosomal dominant gain-of-function mutations in the TSH receptor gene have been demonstrated. In these patients, molecular genetic studies are extremely helpful in therapeutic decision making, as early thyroid ablation is the only effective treatment that avoids the sequelae of long-term hyperthyroidism. Molecular genetic studies are therefore useful in the diagnostic work-up of neonatal thyroid alterations.     

Severe congenital hypothyroidism due to a homozygous mutation of the betaTSH gene.

Isolated TSH deficiency leading to hypothyroidism seems to be a rare condition, escaping the diagnosis by neonatal screening programs, which are based on the primary determination of TSH. This is the first report of a case with an autosomal recessive TSH defect caused by a homozygous mutation of the betaTSH gene that was diagnosed in the early neonatal period. Hypothyroidism in the first child of apparently unrelated parents was suspected because of the classical symptoms of congenital hypothyroidism, which were fully expressed already on the 11th day of life. Routine neonatal TSH-screening on the 4th day of life had been normal, but subsequent determination of serum thyroid hormone levels revealed almost undetectable levels and thyroid hormone substitution was immediately started. Because there was no indication for other pituitary hormone deficiencies, sequence analysis of the betaTSH gene was initiated. A homozygous T deletion in codon 105 was found resulting in a change of a highly conserved cysteine to valine followed by eight altered amino acids and a premature stop codon due to the frame-shift. This altered betaTSH is a biologically inactive peptide. Because of the early development of severe symptoms, it is possible that this altered TSH suppresses the physiologic constitutive activity of the unliganded TSH receptor. Rapid molecular diagnosis in this patient clarified the diagnosis without additional endocrine and imaging studies and it is concluded, that symptoms of hypothyroidism in the neonatal period should result always in an immediate comprehensive work-up of thyroid function including molecular genetic studies irrespective of the screening result.     

Pathology of the TSH receptor

Gain of function and loss of function mutations of the TSH receptor have been implicated in the pathogenesis of various thyroid diseases. Gain of function mutations, when somatic, are the first cause of autonomous nodules; when germline, they are responsible for hereditary non-autoimmune toxic thyroid hyperplasia and for some cases of sporadic congenital hyperthyroidism. A subset of mutations modifying the receptor selectivity have recently been found to be involved in the pathogenesis of familial gestational hyperthyroidism. These mutations are of great interest for understanding the mechanism of receptor activation. Loss of function mutations of the TSH receptor are responsible for different phenotypes ranging from asymptomatic resistance to TSH to overt congenital hypothyroidism.     

Hyperthyroxinämie mit kardialer Symptomatik

Resistance to thyroid hormone (RTH) is a rare autosomal dominant inherited disease, which is usually caused by mutations in the TRβ-gene. The clinical presentation of RTH is highly variable and patients can show signs of euthyroidism, hypothyroidism and/or hyperthyroidism. We report on a 12¹¹/₁₂ year old girl who was admitted to hospital with tachycardia. Laboratory tests showed high levels of serum free T3 and free T4 in the presence of non-suppressed TSH concentrations. Further investigations, including molecular genetic tests, were then performed and revealed a rare case of thyroid hormone resistance. Our case report demonstrates that patients with RTH may manifest only cardiovascular symptoms.     

TSHR is the main causative locus in autosomal recessively inherited thyroid dysgenesis

Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder and results in mental retardation if untreated. Eighty-five percent of CH cases are due to disruptions in thyroid organogenesis and are mostly sporadic, but about 2% of thyroid dysgenesis is familial, indicating the involvement of genetic factors in the aetiology of the disease. In this study, we aimed to investigate the Mendelian (single-gene) causes of non-syndromic and non-goitrous congenital hypothyroidism (CHNG) in consanguineous or multi-case families. Here we report the results of the second part (n=105) of our large cohort (n=244), representing the largest such cohort in the literature, and interpret the overall results of the whole cohort. Additionally, 50 sporadic cases with thyroid dysgenesis and 400 unaffected control subjects were included in the study. In familial cases, first, we performed potential linkage analysis of four known genes causing CHNG (TSHR, PAX8, TSHB, and NKX2-5) using microsatellite markers and then examined the presence of mutations in these genes by direct sequencing. In addition, in silico analyses of the predicted structural effects of TSHR mutations were performed and related to the mutation specific disease phenotype. We detected eight new TSHR mutations and a PAX8 mutation but no mutations in TSHB and NKX2-5. None of the biallelic TSHR mutations detected in familial cases were present in the cohort of 50 sporadic cases. Genotype/phenotype relationships were established between TSHR mutations and resulting clinical presentations. Here we conclude that TSHR mutations are the main detectable cause of autosomal recessively inherited thyroid dysgenesis. We also outline a new genetic testing strategy for the investigation of suspected autosomal recessive non-goitrous CH.     

A Case with Hyperthyroidism Who Had Been Treated with Thyroid Hormone Because of Congenital Hypothyroidism

We encountered a case with hyperthyroidism at the age of 14 who had been diagnosed with congenital hypothyroidism (CH) and had received thyroid hormone replacement therapy. At the age of 16 d, the patient was referred to our hospital because of positive results at neonatal screening for CH. Serum level of TSH was 91.0 μU/ml and serum level of T4 was 6.9 μg/dl. The patient was diagnosed as having hypothyroidism, and hormone replacement therapy was started. Thereafter the dosage of thyroid hormone was adjusted and increased gradually as he grew to a maximum dose of 110 μg/day at the age of 11. Until the age of 13, the patient’s serum levels of TSH were within the normal range; then, at the age of 13 yr and 4 mo, his serum level of TSH dropped to a level below the detectable range. The dosage of administered thyroid hormone was tapered off and eventually eliminated at the age of 14. A thyroid scan and a radioactive iodine uptake test demonstrated a diffuse goiter with homogeneous uptake of radioactive iodine; the uptake rate was 60% at 24 h, and the serum level of TSH receptor antibody (TRAb) was 62.5% at that time. Administration of an antithyroid drug was started after confirmation that our patient had developed hyperthyroidism. There have been no case reports similar to our case.     

Genetic Analysis in Children with Transient Thyroid Dysfunction or Subclinical Hypothyroidism Detected on Neonatal Screening

About 30% of children with elevated TSH levels during neonatal screening have a transient form of disorder. On the other hand, it has been reported that subclinical hypothyroidism persists in late childhood in about 30% of children found to be false-positive during neonatal screening. The aim of this study was to determine whether transient thyroid dysfunction and subclinical hypothyroidism detected during neonatal screening are influenced by genetic background. The TSH receptor (TSHR), thyroid peroxidase (TPO) and dual oxidase 2 (DUOX2) genes, for which it has been reported that heterozygous defects cause neonatal transient thyroid dysfunction, were analyzed. Nine children with transient thyroid dysfunction or subclinical hypothyroidism detected during neonatal screening were studied. One child was heterozygous for a TSHR gene mutation (R450H), and another child was heterozygous for a TPO gene mutation (P883S). No children with mutation of the DUOX2 gene were identified. Genetic background may contribute to development of transient thyroid dysfunction and subclinical hypothyroidism detected during neonatal screening.     

Thyroid function abnormalities among first‐degree relatives of Iranian congenital hypothyroidism neonates

Background: Congenital hypothyroidism (CH) is a relatively common metabolic disease in neonates. Until recent years the disorder was usually regarded as occurring in a sporadic manner. Over the past few years, however, a considerable proportion of familial cases have been identified, and possible roles of autoimmune factors suggested. The aim of the present study was to evaluate abnormality of thyroid function tests in first‐degree relatives of CH neonates and compared this to the normal population. Methods: From 2002 until 2007 thyroid function tests (T4 and thyroid‐stimulating hormone [TSH]) were done in randomly selected CH and normal neonates (n= 194 and n= 350, respectively) and their first‐degree relatives. Most mothers of the CH neonates and control groups were also evaluated for thyroid peroxidase antibody (TPOAb). Results: Thyroid function test in first‐degree relative of neonates with CH (361 parents, 136 siblings) were compared with those in control groups (665 parents, 478 siblings). Abnormal thyroid function tests were found in 85 patients in the CH group versus 96 patients in the control group; hypothyroidism was found in 75 (15.1%) and 57 subjects (5%) person in the CH and control groups, respectively (P < 0.05). Positive TPO antibody was found in 22 mothers (17.3%) of CH neonates in comparison with 65 mothers (32.5%) of control groups (P < 0.05). Frequency of hyperthyroidism in parents of control group had trend to be higher than parents of CH neonates (P= 0.05) Conclusion: Familial and genetic components play a role in inheritance of CH, but maternal thyroid autoimmunity may not play an important role in the development of CH in Iran.     

Pendred syndrome among patients with congenital hypothyroidism detected by neonatalscreening: identification of two novel <Emphasis Type="Italic">PDS/SLC26A4</Emphasis> mutations

Pendred syndrome is an autosomal recessive disorder characterised by sensorineural hearing loss and thyroid dyshormonogenesis. It is caused by mutations in the PDS/SLC26A4 gene (OMIM 605646) encoding for pendrin. Hypothyroidism in Pendred syndrome can be—although rarely—present from birth and therefore diagnosed by neonatal screening. The aim of our study was to identify patients with Pendred syndrome among a historical cohort of patients with congenital hypothyroidism (CH) identified by neonatal screening, and to find their mutations in the PDS/SLC26A4 gene. We investigated 197 Czech Caucasian children with CH detected by the neonatal screening between the years 1985 and 2005. The clinical diagnosis of Pendred syndrome was based on the laboratory and sonographic signs of thyroid dyshormonogenesis in association with sensorineural hearing loss. In subjects clinically diagnosed with Pendred syndrome, we sequenced all exons and exon-intron boundaries of the PDS/SLC26A4 gene. Hearing loss was present in 10/197 children with screening-detected CH. Of these, three fulfilled the diagnostic criteria of Pendred syndrome. Two patients were compound heterozygotes for PDS/SLC26A4 mutations: patient 1 carried c.2089+1G>A / c.3G>C and patient 2 carried p.Tyr530His / p.Val422Asp. Two of the four identified mutations were novel (c.3G>C in patient 1 and p.Val422Asp in patient 2). The third patient was free of mutations in the PDS/SLC26A4 gene, representing a phenocopy. In conclusion, our results indicate the rarity of Pendred syndrome as a cause of CH. The identification of two novel mutations expands the spectrum of mutations in the PDS/SLC26A4 gene and emphasizes their marked allelic heterogeneity. The study was supported by grants of the Czech Ministry of Education (MSM 0021620814) and Charles University in Prague (GAUK 2008/2007).     

非典型溶血尿毒综合征分子遗传学研究进展

非典型溶血尿毒综合征是一种罕见的有遗传倾向的疾病,易患基因主要是补体旁路途径活化的调控基因:补体因子H基因、膜辅助蛋白基因和补体因子Ⅰ基因.但其总突变率约为50%,突变类型包括错义突变、无义突变、缺失突变、插入突变和剪切位点突变.遗传方式有常染色体隐性遗传和常染色体显性遗传,显性遗传的三个突变基因均为不完全外显.     

Newborn screening for congenital hypothyroidism

Most neonates born with congenital hypothyroidism (CH) have normal appearance and no detectable physical signs. Hypothyroidism in the newborn period is almost always overlooked and delayed diagnosis leads to the most severe outcome of CH, mental retardation, emphasizing the importance of neonatal screening. Blood spot T4 or TSH or both can be used in neonatal screening for CH. The latter, which is more sensitive, is not cost effective, so the first two are used in different programs in the world. TSH screening was shown to be more specific in the diagnosis of CH; T4 screening is more sensitive in detecting newborns especially with rare hypothalamic-pituitary hypothyroidism, but less specific with a high frequency of false positives mainly in low birth weight and premature infants. The time at which the sample is taken may vary between centers, with the majority taking blood from a heel prick after 24 hours of age to minimize the false positive high TSH due to the physiological neonatal TSH surge that elevates TSH levels and causes dynamic T4 and T3 changes in the first 1 or 2 days after birth. Early discharge of mothers postpartum has increased the ratio of false positive TSH elevations. Although transient hypothyroidism may occur frequently, all suspected infants should be treated as having CH for the first 3 years of life, taking into account the risks of mental retardation. A reevaluation after 3 years is needed in such patients. The goal of initial therapy in CH is to minimize neonatal central nervous system exposure to hypothyroidism by normalizing thyroid function, as reflected by T4 and TSH levels, as rapidly as possible. Iodine deficiency is the most important cause of CH worldwide. Iodine is essential for thyroid hormone synthesis and is present in soil, water and air. Prevention of iodine deficiency can be by iodized salt, iodized oil, iodized bread or iodine tablets.     

先天性甲状腺功能减低症筛查及治疗效果分析

目的了解先天性甲状腺功能减低症(CH)的筛查及替代治疗结果。方法回顾性分析2003年7月—2015年7月采用时间分辨荧光免疫法测定新生儿促甲状腺激素(TSH)水平筛查CH的资料;阳性召回的可疑患儿采用化学免疫发光法测定血清甲状腺功能,确诊者予左旋甲状腺素钠替代治疗并定期随访。结果 12年来共筛查新生儿1 228 289例,确诊950例,CH发病率1/1 293。接受正规治疗、随访满2年及以上的635例CH患儿中,488例(76.85%)为永久性CH,147例(23.15%)为暂时性CH。CH患儿随访至1岁和3岁时,体格生长和发育商(DQ)无异常。结论新生儿筛查可早期诊断CH,早期实施替代治疗。     

Congenital hypothyroidism caused by a novel homozygous mutation in the thyroglobulin gene

Congenital hypothyroidism (CH) due to thyroglobulin (TG) deficit is an autosomal recessive disease (OMIM #274700) characterized by hypothyroidism, goiter, low serum TG, and a negative perchlorate discharge test. The aim of this study was to perform the genetic analysis of the TG gene in two sisters born from consanguineus parents and affected by CH and low serum TG levels. The index patient and her sister were identified at neonatal screening for CH and treated with L-thyroxine (L-T4). After discontinuation of L-T4 therapy, hypothyroidism was confirmed, serum TG was undetectable, and no organification defect after ¹²³I scintigraphy and perchlorate test was shown; thyroid ultrasound showed a eutopic gland of normal size. DNA was extracted from peripheral white blood cells of the two sisters and the father. All 48 exons of TG gene were amplified by polymerase chain reaction and subjected to direct sequencing. A novel homozygous point mutation in exon 10 of TG gene was identified in the patient and her sister. The mutation determined a stop codon at position 768 (R768X) resulting in an early truncated protein or in the complete absence of the protein. The father (euthyroid) was heterozygous carrier of the mutation. Conclusion: Genetic analysis of TG gene was performed in two sisters affected by CH. A novel point mutation of the TG gene determining a stop codon at position 768 of the protein was identified. The early truncated nonfunctioning protein or the absence of the protein due to the premature degradation of abnormal mRNA may be responsible of the observed phenotype.     

An activating mutation of the thyrotropin receptor gene in hereditary non-autoimmune hyperthyroidism

The thyroid stimulating hormone (TSH) receptor gene displays a diverse spectrum of activating and inactivating mutations. We report a germline activating mutation M463V of the TSH receptor gene in two siblings with hereditary non-autoimmune hyperthyroidism. The onset of disease in the affected members of the pedigree occurred during childhood or adolescence. The significance of diagnosing activating TSHR mutations lies in therapeutic management and genetic counseling; thyroid ablation is advocated as first line treatment.     

A family with a novel TSH receptor activating germline mutation (p.Ala485Val)

Autosomal dominant nonautoimmune hyperthyroidism (ADNAH) is caused by gain of function mutations in the TSH receptor (TSHr) gene and characterized by toxic thyroid hyperplasia with a variable age of onset in the absence of thyroid antibodies and clinical symptoms of autoimmune thyroid disease in at least two generations. We report here a Turkish family with a novel TSHr gene mutation with distinct features all consistent with ADNAH. Thyroid function tests of the proband were as follows: free T3: 13.1 pg/ml (N: 1.8–4.6); free T4: 5.1 ng/dl (N: 0.9–1.7); TSH: 0.01 μIU/ml (N: 0.2–4.2); and TSH receptor antibody: 2 IU/ml (N: 0–10). A heterozygous missense mutation in exon 10 of the TSHr gene (c.1454C>T) resulting in the substitution of valine for alanine at codon 485 (p.Ala485Val) was found in the father and his son and daughter. This mutation had arisen de novo in the father. Functional studies of the novel TSHr germline mutation demonstrated a higher constitutive activation of adenyl cyclase than wild type without any effect on phospholipase C activity. In conclusion, our data indicate that gain of function germline mutations in the TSHr gene should be investigated in families with members suffering from thyrotoxicosis and progressive growth of goiter, but without clinical and biochemical evidence of autoimmune thyroid disease. In addition, patients harboring the same mutation of the TSHr gene may show wide phenotypic variability with respect to the age at onset, and severity of hyperthyroidism and thyroid growth.     

先天性甲状腺功能减退症患儿GNAS和THRA基因突变分析

目的 对70例先天性甲状腺功能减退症（CH）患儿的刺激性G蛋白α亚基（GNAS）基因和甲状腺素受体α（THRA）基因进行二代测序分析,并初步探讨GNAS和THRA基因突变型与CH患儿的临床表现型之间的关系。方法 选取70例通过新生儿筛查确诊为CH的患儿,采集外周血并进行DNA样本提取,利用二代测序技术对GNAS和THRA基因进行突变筛查,利用生物信息学软件分析基因突变的致病性。结果 70例CH患儿中,3例患儿（4%）检出9种GNAS基因的错义突变（包括3种已知基因突变和6种新突变）,4例患儿检出同1种THRA基因多态c.508A > G（p.I170V）。经过生物信息学软件预测和ACMG/AMP指南分析发现2种GNAS基因突变[c.301C > T（p.R101C）、c.334G > A（p.E112K）]致病的可能性大。3例携带GNAS基因突变的患儿存在不同程度的甲状腺功能低下表现。结论 GNAS基因突变与CH的发病有关,患儿的临床表现存在较大的异质性;THRA基因突变可能与CH的发病无相关性。