Differential diagnosis between Pendred and pseudo-Pendred syndromes: clinical, radiologic, and molecular studies

The disease gene for Pendred syndrome has been recently characterized and named PDS. It codes for a transmembrane protein called pendrin, which is highly expressed at the apical surface of the thyroid cell and functions as a transporter of chloride and iodide. Pendrin is also expressed at the inner ear level, where it appears to be involved in the maintenance of the endolymph homeostasis in the membranous labyrinth, and in the kidney, where it mediates chloride-formate exchange and bicarbonate secretion. Mutations in the PDS gene and the consequent impaired function of pendrin leads to the classic phenotype of Pendred syndrome, i.e. dyshormonogenic goiter and congenital sensorineural hearing loss. In the present study, we performed a detailed clinical, radiologic, and molecular analysis of six families presenting with clinical diagnosis of Pendred syndrome. In two families a homozygous pattern for PDS mutations was found, whereas the affected members of the other four families were compound heterozygotes. One family did not harbor PDS mutations. Among the four novel mutations described, one is a transversion in exon 2 (84C>A), leading to the substitution S28R. Two other novel mutations lie in exon 4 (398T>A) and in exon 16 (1790T>C), leading to the substitutions S133T and L597S, respectively. The fourth novel mutation (1614+1G>A) is located in the first base pair of intron 14, probably affecting the splicing of the PDS gene. Clinically, all patients had goiter with positive perchlorate test, hypothyroidism, and severe or profound sensorineural hearing loss. In all the individuals harboring PDS mutations, but not in the family without PDS mutations, inner ear malformations, such as enlargement of the vestibular aqueduct and of the endolymphatic duct and sac, were documented. The pseudo-Pendred phenotype exhibited by the family without PDS mutations is likely caused by an autoimmune thyroid disease associated with a sensorineural hearing loss of different origin.     

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).     

The association of thyroid dyshormonogenesis and deafness (Pendred syndrome): Experience of the Victorian Neonatal Thyroid Screening Programme

Between 1977 and 1989, the Victorian Neonatal Thyroid Screening Programme detected five subjects with thyroid dyshormonogenesis and sensorineural deafness. These patients have been diagnosed as having Pendred syndrome. In two of the children, thyroid function tests which were initially abnormal at birth returned to normal spontaneously without treatment. However, hypothyroidism subsequently recurred and the children required thyroxine therapy. These two children could have been mistakenly diagnosed as having transient hypothyroidism. The detection of five patients with Pendred syndrome illustrates the importance of audiological assessment in all babies with thyroid dyshormonogenesis in whom there is increased uptake of isotope on thyroid scanning. In our experience, hearing loss in patients with Pendred syndrome may be progressive over time, so that repeated audiological assessments are necessary.     

Identification of SLC26A4 gene mutations in Iranian families with hereditary hearing impairment

Mutations in the SLC26A4 gene at the DFNB4 locus are responsible for Pendred syndrome and non-syndromic hereditary hearing loss (DFNB4). This study included 80 nuclear families with two or more siblings segregating presumed autosomal recessive hearing loss. All deaf persons tested negative for mutations in GJB2 at the DFNB1 locus and were, therefore, screened for autozygosity by descent (ABD) using short tandem repeat polymorphisms (STRPs) that flanked SLC26A4. In 12 families, homozygosity for STRPs suggested possible ABD in this genomic region. Affected individuals in five families had a positive perchlorate discharge test. Sequence analysis of SLC26A4 identified ten mutations in eight families (T420I, 1197delT, G334V, R409H, T721M, R79X, S448L, L597S, 965insA and L445W), of which, four are novel (T420I, G334V, 965insA and R79X). These results imply that Pendred syndrome is the most prevalent form of syndromic hereditary hearing loss in Iran.     

Solitary thyroid nodule as presenting symptom of Pendred syndrome caused by a novel splice-site mutation in intron 8 of the <Emphasis Type="Italic"> SLC26A4</Emphasis> gene

Thyroid nodules are a rare occurrence in children but represent an important clinical problem because of the possibility of malignancy. We report the case of a 4-year-old boy with sensorineural deafness, who presented with a painless mass in the right anterior cervical region. Cervical ultrasound demonstrated a solid nodule (1.4×2.5×1.7 cm) in the right thyroid lobe. Thyroid function tests revealed compensated hypothyroidism (free T4 1.0 ng/dl; TSH 57 mIU/l) with no detectable thyroid antibodies. A ^99m Tc thyroid scan showed a generalised slightly increased tracer retention (4.6%) with an enlarged right lobe, without distinct nodules. A fine-needle aspiration biopsy revealed normal follicular cells. The boy was treated with l-thyroxine which resulted in a complete clinical and sonographical disappearance of the nodule. A CT scan of temporal bones revealed a bilaterally enlarged vestibular aqueduct with Mondini malformation of the cochlea. The combination of all these symptoms suggested the diagnosis of Pendred syndrome (PDS), a disorder characterised by congenital sensorineural hearing loss and a variable degree of thyromegaly due to mutations in the SLC26A4/PDS gene. DNA analysis disclosed a so far unreported homozygous splice site mutation (1002–4 C>G) in intron 8 of the SLC26A4 gene confirming this diagnosis. Conclusion: a solitary thyroid nodule may therefore be another presenting symptom of thyroid involvement in Pendred syndromeAbbreviation PDS Pendred syndrome     

Genetic deafness:the primary cause of sensorineural hearing loss in children]

Genetically-transferred hearing impairments account for more than 50% of cases of pediatric sensorineural hearing defects. Multiple clinical aspects are involved in genetic hearing impairment, including the involvement of other organs, genetic inheritance, and the degree and age at onset of hearing loss. Diagnosis relies on family history, on the systematic investigation of the symptomatology including an associated syndrome, and audiometry testing in parents and siblings. Analysis of the connexin 26 gene is also indicated, as it is frequently involved in this disorder. Further genetic analysis in affected families will aid in detecting other as yet unidentified genes responsible for hearing impairment.     

Thiamine-responsive megaloblastic anaemia: a cause of syndromic diabetes in childhood

Thiamine-responsive megaloblastic anaemia (TRMA) is a rare autosomal recessive condition, characterized by megaloblastic anaemia, non-autoimmune diabetes mellitus, and sensorineural hearing loss. We describe three infants with TRMA from two consanguineous Pakistani families, who were not known to be related but originated from the same area in Pakistan. All children were homozygous, and the parents were heterozygous for a c.196G>T mutation in the SLC19A2 gene on chromosome 1q23.3, which encodes a high-affinity thiamine transporter. The result is an abnormal thiamine transportation and vitamin deficiency in the cells. Thiamine in high doses (100-200 mg/d) reversed the anaemia in all our patients. Two patients discontinued insulin treatment successfully after a short period, while the third patient had to continue with insulin. The hearing loss persisted in all three children. The diagnosis of TRMA should be suspected in patients with syndromic diabetes including hearing loss and anaemia, even if the latter is only very mild and, particularly, in the case of consanguinity.     

The Long–Evans Cinnamon rat: An animal model for Wilson's disease

The Long-Evans Cinnamon (LEC) rat is known to develop hepatitis and liver cancer spontaneously, phenomena attributed to abnormal copper metabolism. This mutant strain of rat shows some clinical features that are similar to those of Wilson's disease, including excessive copper in the liver, reduced excretion of copper into bile, a reduced level of serum copper and a remarkable decrease in serum ceruloplasmin activity. Molecular studies have revealed that the copper transporting P-type ATPase, atp7b, which is the rat gene homologous to human ATP7B, was found to be defective in the LEC rat. These observations have confirmed that the LEC rat is a rodent model for Wilson's disease. In addition, recent studies have suggested that the ATP7B protein is involved in the intracellular transport of hepatic copper. The absence or diminution of ATP7B function results in abnormal copper metabolism in the LEC rat and in patients with Wilson's disease.     

A contiguous deletion syndrome of X-linked agammaglobulinemia and sensorineural deafness

Hearing loss in patients with X-linked agammaglobulinemia is often attributed to recurrent infections. However, recent genetic studies suggest a different etiology in some patients. We present three unrelated patients, 6, 9, and 14 years of age, with large deletions of the terminal portion of the Bruton tyrosine kinase ( Btk ) gene extending 4.2–19 kb beyond the 3' end of the gene. The DNA immediately downstream of the 3' end of Btk contains the deafness-dystonia protein gene ( DDP ). Mutations in this gene have recently been shown to underlie the Mohr–Tranebjaerg syndrome, which is characterized by sensorineural deafness, dystonia, and mental deficiency. Besides the immunodeficiency, our patients exhibited progressive sensorineural deafness. The clue to an associated hearing problem was delayed development of speech in one patient and post-lingual deafness noticed between the age of 3–4 years in the other two. These patients have not yet exhibited significant associated neurologic deficits.     

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.     

Allan-Herndon-Dudley syndrome

Allan-Herndon-Dudley Syndrome (AHDS) is a rare X-linked disorder caused by mutation in the gene encoding the monocarboxylate transporter-8. Abnormal transport function is reflected by elevated free T3 and decreased free T4 levels along with clinical features characterized by neurological abnormalities including global developmental delay, central hypotonia, rotatory nystagmus, impaired hearing, spasticity and contractures of joints. We report a child with classical clinical features along with confirmatory deranged thyroid levels in blood.     

Van der Woude syndrome in combination with ring chromosome 18

7-month-old girl with a combination of van der Woude syndrome and ring chromosome 18 showed the following malformations: medial palate cleft, fistulas of the lower lips, hypertelorism, epicanthus, antimongoloid position of the eyelids, a small hymenal appendix, plantar placing of the third toe, atrial septum defect, stenosis of the auditory canal. The combination of fistulas of the lower lip and cleft lip or palate already established the diagnosis of Van der Woude Syndrome. Because of the additional malformations observed a chromosome analysis was performed which demonstrated a ring chromosome 18. The phenotypic features of ring-chromosome 18, a 18p-/18q- syndrome, vary according to the extend of deletion of the short or long arm. However, all patients show craniofacial dysmorphism, intellectual and developmental retardation, defective hearing, speech disorder, and more than 50% have stenosis or atresia of the auditory canal.     

Glucose transporter 1 deficiency syndrome and hemiplegic migraines as a dominant presenting clinical feature

Glucose transporter 1 deficiency syndrome (OMIM 606777) is a treatable epileptic encephalopathy caused by mutations in the SLC2A1 gene (OMIM 138140) causing impaired glucose transport into the brain. The classical phenotype is associated with seizures, developmental delay, ataxia and spasticity; however, milder phenotypes are emerging. We describe an 8‐year‐old boy with glucose transporter 1 deficiency syndrome whose clinical presentation was dominated by hemiplegic migraines that resolved with institution of a modified Atkins diet.     

GJB2基因及其诊断筛查技术研究进展

耳聋基因GJB2定位于13q11-q12,编码connexin26(CX26)蛋白.在常染色体隐形遗传的非综合征性耳聋中,有50%的患者存在着GJB2基因的突变,然而在不同种族中,GJB2基因的突变位点也是不同的.35delG是欧美人群主要的突变形式;突变位点167delT在犹太耳聋人群中多见;而在亚裔人群中,235delC突变占有极大的比例.由于GJB2基因在遗传性耳聋中的特殊地位,因此对于GJB2基因的诊断及筛查技术就显得尤为重要.在新生儿听力筛查基础上,融入耳聋易患基因分子水平筛查,在早期发现和干预先天性听力损失方面发挥着重要作用.     

Noonan's and DiGeorge syndromes with monosomy 22q11.

A boy with the dysmorphic features of Noonan's syndrome and pulmonary valve stenosis who had evidence of hypoparathyroidism and abnormal T lymphocyte numbers in the neonatal period is reported. He had a normal karyotype but molecular analysis revealed a submicroscopic deletion within chromosome 22q11, the region deleted in DiGeorge syndrome. Thus this child has both Noonan's syndrome and DiGeorge syndrome; 22q11 is a candidate region for a gene defective in Noonan's syndrome.     

Noonan's and DiGeorge syndromes with monosomy 22q11

A boy with the dysmorphic features of Noonan's syndrome and pulmonary valve stenosis who had evidence of hypoparathyroidism and abnormal T lymphocyte numbers in the neonatal period is reported. He had a normal karyotype but molecular analysis revealed a submicroscopic deletion within chromosome 22q11, the region deleted in DiGeorge syndrome. Thus this child has both Noonan's syndrome and DiGeorge syndrome; 22q11 is a candidate region for a gene defective in Noonan's syndrome.     

The Langer-Giedion-syndrome (tricho-rhino-phalangeal syndrome,type II)

A 15-year-old girl with the Langer-Giedion-syndrome (tricho-rhino-phalangeal syndrome, type II) is presented. The features are multiple exostoses, sparse, fine hair and an abnormal face and hands. X-ray examination reveals exostoses and abnormal epiphyses. In this case intelligence is normal; there is severe sensorineural deafness (60–80 dB hearing loss).The genetic aspects of the syndrome are discussed. Address for offrint requests: Department of Pediatrics, University Hospital of Amsterdam, Binnengasthuis, Grimburgwal 10, 1012 GA Amsterdam, The Netherlands     

Inborn Errors of Peroxisome Biogenesis and Brain Malformation: Clinical and Biochemical Studies*

Zellweger's cerebro-hepato-renal syndrome is characterized by the absence of peroxisomes, severe neurologic manifestations, and neuropathological findings such as polymicrogyria and neuronal heterotopia which are based on disturbances of neuronal migration. We investigated the pathogenesis of peroxisome-deficient disorders in attempts to clarify the molecular basis of these brain dysgenesis. Complementation analysis revealed that at least 9 genes contribute to the formation of peroxisomes. One of these gene products, peroxisome assembly factor-1 (PAF-1), was isolated, using a functional cloning method and a mutant Chinese hamster ovary cell line with defective peroxisomes. PAF-1 restored the peroxisomes and biochemical abnormalities in fibroblasts from patients with Zellweger syndrome and who belonged to complementation group F. Defects in PAF-1 would result in dysfunction of peroxisomal membrane or in the transport machinery of peroxisomal proteins, and metabolic disturbances such as accumulation of very long chain fatty acids and defects in plasmalogen may occur.     

Hearing defects in cystic fibrosis

34 children with cystic fibrosis were investigated for defective hearing. In 11 cases a pathological audiometric finding was observed; 10 of the children had conductive hearing loss, 1 had sensorineural hearing loss. 4 children who were too young for exact subjective audiometry were investigated with the Evoked Response Audiometry method; none of them had an abnormal result.No correlation between the defect and the severity and duration of cystic fibrosis could be demonstrated. The reason for the defect seems to be the hypobaric pressure in the middle ear, possibly caused by pathological secretion of the mucosal glands of the Eustachian tube with resulting obstruction. Ventilation of the tube was therapeutically successfull in 4 out of 5 cases and lead to normalization of the audiogram.A shorter version of this paper was presented at the 3rd Meeting of the European Working Group for Cystic Fibrosis, Erbach, Germany, September 6./7. 1972.