A Homozygous Nonsense Thyroid Peroxidase Mutation (R540X) Consistently Causes Congenital Hypothyroidism in Two Siblings Born to a Consanguineous Family

Objective:

Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder, and mutations in the thyroid peroxidase (TPO) gene have been reported to cause the disease. Our aim in this study was to determine the genetic basis of CH in two affected children coming from a consanguineous family.

Methods:

First, we investigated the potential genetic linkage of the family to any known CH locus using microsatellite markers and then screened for mutations in the linked gene by Sanger sequencing. By using next-generation sequencing, we also checked if any other mutation was present in the remaining 10 causative CH genes.

Results:

The family showed potential linkage to the TPO gene, and we detected a homozygous nonsense mutation (R540X) in both cases. The two patients had total iodide organification defect (TIOD). Both the microsatellite marker haplotypes and the mutation segregated with the disease status in the family, i.e. all healthy subjects were either heterozygous carriers or homozygous wild-type, confirming the pathogenic nature of the mutation. Neither was the mutation present in any of the 400 control chromosomes nor were there any other mutations in the remaining causative CH genes.

Conclusion:

This study proves the pathogenicity of R540X mutation and demonstrates the strong genotype/phenotype correlation associated with this mutation. It also highlights the power of working with familial cases in revealing the molecular basis of CH and in establishing accurate genotype/phenotype relationships associated with disease causing mutations.     

Novel mutations of the thyroid peroxidase gene in patients with permanent congenital hypothyroidism.

OBJECTIVE: It is suggested that iodide organification defects account for 10% of all cases with congenital hypothyroidism (CH). One candidate gene for these defects is the thyroid peroxidase (TPO) gene. DESIGN: Exons 2, 8-10 and 14 of the TPO gene were examined in 30 patients with permanent CH without a family history of CH. This group was characterized by the presence of an orthotopic thyroid gland and elevated TSH levels. METHODS: The mutational screening was performed by single-strand conformational polymorphism followed by sequence analysis of fragments with abnormal migration patterns and by restriction enzyme analysis. RESULTS: In four patients we were able to identify mutations on both alleles which have not been described so far. One patient was a carrier of a new homozygous point mutation in exon 9 resulting in an exchange from Leu to Pro at codon 458. Another patient was found to be compound heterozygous for two mutations, a 20 bp duplication in exon 2 and a new mutation in exon 9 (Arg491His). Two brothers of consanguineous parents showed a homozygous T deletion in exon 14 at position 2512. CONCLUSIONS: Our findings confirm the genetic heterogeneity of TPO defects and support the suggested prevalence of organification defects.     

The Missense Alteration A5T of the Thyroid Peroxidase Gene is Pathogenic and Associated with Mild Congenital Hypothyroidism

Congenital hypothyroidism (CH) occurs with a prevalence of approximately 1:4000 live births. Defects of thyroid hormone synthesis account for 15-20% of these cases. Thyroid peroxidase (TPO) gene is the most common cause for dyshormonogenesis. So far, more than 60 mutations in the TPO gene have been described, resulting in a variable decrease in TPO bioactivity. We present an 8-day-old male with mild CH who was identified to have a G to A transition in the fifth codon of the TPO gene (c.13G>A; p.Ala5Thr). The unaffected family members were heterozygous carriers of the mutation, whereas 400 healthy individuals of the same ethnic background did not have the mutation. Mutation analysis of 11 known causative CH genes and 4 of our own strong candidate genes with next-generation sequencing revealed no mutations in the patient nor in any other family members. The results of in silico functional analyses indicated partial loss-of-function (LOF) in the resulting enzyme molecule due to mutation. The patient’s clinical finding s were consistent with the effect of this partial LOF of the mutation. In conclusion, we strongly believe that A5T alteration in the TPO gene is actually pathogenic and suggest that it should be classified as a mutation.     

Hereditary thrombocythaemia is a genetically heterogeneous disorder: exclusion of TPO and MPL in two families with hereditary thrombocythaemia

Hereditary thrombocythaemia (HT) is an autosomal dominant disorder with clinical presentation and complications resembling sporadic essential thrombocythaemia (ET). Mutations in the thrombopoietin (TPO) gene causing overproduction of TPO and elevated TPO serum levels have been found previously in three families with HT. Here, we present evidence for genetic heterogeneity by demonstrating that HT in a Spanish and a US family is caused by genes other than TPO. Affected family members in both families had normal TPO serum levels. Genetic linkage analysis with TPO microsatellite markers excluded TPO as the disease gene in the Spanish HT family, and sequencing of the TPO gene revealed no mutations in the propositus of the US family. To test a role for MPL, the gene for the TPO receptor, we identified three single nucleotide polymorphisms (SNP) and a novel polymorphic CA microsatellite marker. By linkage analysis, we excluded MPL as the cause of HT in the Spanish family. Interestingly, mapping of the CA microsatellite marker to a region 40.5 kb upstream of MPL revealed the presence of sequences from the TIE gene, which encodes a tyrosine kinase receptor expressed on megakaryocytes and endothelial cells. Thus, MPL and TIE are in close physical proximity, and the CA microsatellite described here will be a useful genetic marker for both genes.     

Exome sequencing identifies MPL as a causative gene in familial aplastic anemia

The primary cause of aplastic anemia remains unknown in many patients. The aim of this study was to clarify the genetic cause of familial aplastic anemia. Genomic DNA of an affected individual from a multiplex consanguineous family was hybridized to a Nimblegen exome library before being sequenced on a GAIIx genome analyzer. Once the disease causing homozygous mutation had been confirmed in the consanguineous family, this gene was then analyzed for mutation in 33 uncharacterized index cases of aplastic anemia (<13 years) using denaturing HPLC. Abnormal traces were confirmed by direct sequencing. Exome sequencing identified a novel homozygous nonsense mutation in the thrombopoietin receptor gene MPL. An additional novel homozygous MPL mutation was identified in the screen of 33 aplastic anemia patients. This study shows for the first time a link between homozygous MPL mutations and familial aplastic anemia. It also highlights the important role of MPL in trilineage hematopoiesis.     

Pseudodominant inheritance of goitrous congenital hypothyroidism caused by TPO mutations: molecular and in silico studies

CONTEXT AND OBJECTIVE: Most cases of goitrous congenital hypothyroidism (CH) from thyroid dyshormonogenesis 1) follow a recessive mode of inheritance and 2) are due to mutations in the thyroid peroxidase gene (TPO). We report the genetic mechanism underlying the apparently dominant inheritance of goitrous CH in a nonconsanguineous family of French Canadian origin. DESIGN, SETTING, AND PARTICIPANTS: Two brothers identified by newborn TSH screening had severe hypothyroidism and a goiter with increased (99m)Tc uptake. The mother was euthyroid, but the father and two paternal uncles had also been diagnosed with goitrous CH. After having excluded PAX8 gene mutations, we hypothesized that the underlying defect could be TPO mutations. RESULTS: Both compound heterozygous siblings had inherited a mutant TPO allele carried by their mother (c.1496delC; p.Pro499Argfs2X), and from their father, one brother had inherited a missense mutation (c.1978C-->G; p.Gln660Glu) and the other an insertion (c.1955insT; p.Phe653Valfs15X). The thyroid gland of one uncle who is a compound heterozygote for TPO mutations (p.Phe653Valfs15X/p.Gln660Glu) was removed because of concurrent multiple endocrine neoplasia type 2A. Immunohistochemistry revealed normal TPO staining, implying that Gln660Glu TPO is expressed properly. Modeling of this mutant in silico suggests that its three-dimensional structure is conserved, whereas the electrostatic binding energy between the Gln660Glu TPO and its heme group becomes repulsive. CONCLUSION: We report a pedigree presenting with pseudodominant goitrous CH due to segregation of three different TPO mutations. Although goitrous CH generally follows a recessive mode of inheritance, the high frequency of TPO mutations carriers may lead to pseudodominant inheritance.     

High prevalence of thyroid peroxidase gene mutations in patients with thyroid dyshormonogenesis

OBJECTIVE: Thyroid dyshormonogenesis is a genetically heterogeneous group of inherited disorders in the enzymatic cascade of thyroid hormone synthesis that result in congenital hypothyroidism (CH). Thyroid peroxidase gene (TPO) mutations are one of the most common causes of thyroid dyshormonogenesis. The aim of this study was to identify TPO gene defects in a cohort of patients with thyroid dyshormonogenesis from Slovenia, Bosnia, and Slovakia. DESIGN AND METHODS: Forty-three patients with permanent CH and orthoptic thyroid glands from 39 unrelated families participated in the study. Mutational analysis of the TPO gene and part of its promoter consisted of single-stranded conformation polymorphism analysis, sequencing, and restriction fragment length polymorphism (RFLP) analysis. Results: TPO gene mutations were identified in 46% of participants. Seven different mutations were identified, four mutations of these being novel, namely 613C > T (R175X), 1519_1539del (A477_N483del), 2089G > A (G667S), and 2669G > A (G860R). Only a single allele mutation was identified in 65% of the TPO mutation carriers. CONCLUSIONS: The results showed a higher prevalence of TPO gene mutations in thyroid dyshormonogenesis when compared with published studies. The high percentage of single allele mutations implied possible intronic or regulatory TPO gene mutations or monoallelic expression.     

Clinical and genetic characteristics of congenital hypothyroidism due to mutations in the thyroid peroxidase (TPO) gene in Israelis

OBJECTIVES: Iodide organification defect (IOD) is characterized by a reduced ability of the thyroid gland to retain iodide and results in hypothyroidism. Mutations in the thyroid peroxidase (TPO) gene are a frequent cause of IOD. While TPO mutations have been identified in various populations, none have been reported in Israeli patients with IOD. The objectives of this study were to characterize the molecular basis of IOD in an Israeli Arab-Muslim population and to analyse the clinical, neurological and imaging data of patients with TPO mutations followed for up to 29 years. PATIENTS: Twenty-two patients from six core families with congenital hypothyroidism (CH) and IOD living in the same region. DESIGN AND MEASUREMENTS: All subjects underwent clinical, hormonal and imaging evaluation. The TPO gene was directly sequenced and the presence of specific mutations among family members was determined by restriction fragment length polymorphism (RFLP). RESULTS: All patients had congenital and persistent primary hypothyroidism. The thyroid gland was demonstrated in all subjects by technetium (99mTc) scans. A positive perchlorate discharge test (mean 87%) was indicative of IOD. Enlargement of the thyroid gland was shown in 64% of our patients, mostly with multinodular appearance, and in some with retrosternal invasion. Neurological complications were observed in 13 patients (59%). Four subjects, who carry two different TPO mutations, had sensorineural deafness. Two previously described TPO gene mutations [G1567A (G493S) and C1708T (R540X)] and one novel TPO gene mutation [C965T (S292F)] were identified. The two previously described mutations were present in 90% of the subjects. Haplotyping suggested a distant common ancestry for each of these two mutations. CONCLUSIONS: Three different TPO gene mutations were found to be responsible for IOD in a consanguineous Israeli population. The high rate of development of multinodular glands (MNGs) in our cohort of patients indicates the need for long-term follow-up of patients with TPO gene mutations.     

Mutation screening of the thyroid peroxidase gene in a cohort of 55 Portuguese patients with congenital hypothyroidism

OBJECTIVE: Defects in the human thyroid peroxidase (TPO) gene are reported to be one of the causes of congenital hypothyroidism (CH) due to a total iodide organification defect. The aim of the present study was to determine the nature and frequency of TPO gene mutations in patients with CH, characterised by elevated TSH levels and orthotopic thyroid gland, identified in the Portuguese National Neonatal Screening Programme. SUBJECTS AND METHODS: The sample comprised 55 patients, from 53 unrelated families, with follow-up in the endocrinology clinics of the treatment centres of Porto and Lisbon. Mutation screening in the TPO gene (exons 1-17) was performed by single-strand conformational analysis followed by sequencing of fragments with abnormal migration patterns. RESULTS: Eight different mutations were detected in 13 patients (seven homozygotes and six compound heterozygotes). Novel mutations included three missense mutations, namely 391T > C (S131P), 1274A > G (N425S) and 2512T > A (C838S), as well as the predictable splice mutation 2748G > A (Q916Q/spl?). The undocumented polymorphism 180-47A > C was also detected. CONCLUSION: The results are in accordance with previous observations confirming the genetic heterogeneity of TPO defects. The proportion of patients in which the aetiology was determined justifies the implementation of this molecular testing in our CH patients with dyshormonogenesis.     

Congenital goitrous hypothyroidism: mutation analysis in the thyroid peroxidase gene

Background Iodide organification defect (IOD) is characterized by a reduced ability of the thyroid gland to retain iodide resulting in hypothyroidism. Mutations in thyroid peroxidase (TPO) gene appear to be the most common cause of IOD and are commonly inherited in an autosomal recessive fashion. The TPO gene is located on the chromosome 2p25. It comprises 17 exons, covers approximately 150 kb of genomic DNA and codes 933 amino acids. Objetives In this study, we characterize the clinical and molecular basis of seven patients from four unrelated families with congenital hypothyroidism (CH) because of IOD. Design and Methods All patients underwent clinical, biochemical and imaging evaluation. The promoter and the complete coding regions of the human TPO along with the flanking intronic regions were analysed by single‐strand conformation polymorphism analysis and direct DNA sequencing. Segregation analysis of mutations was carried out, and the effect of the novel missense identified mutations was investigated by ‘in silico’ studies. Results All subjects had congenital and persistent primary hypothyroidism. Three novel mutations: c.796C>T [p.Q266X], c.1784G>A [p.R595K] and c.2000G>A [p.G667D] and a previously reported mutation: c.1186_1187insGGCC [p.R396fsX472] have been identified. Four patients were compound heterozygous for p.R396fsX472/p.R595K mutations, two patients were homozygous for p.R595K, and the remaining patient was a compound heterozygous for p.Q266X/p.G667D. Conclusions Our findings confirm the genetic heterogeneity of TPO defects and the importance of the implementation of molecular studies to determinate the aetiology of the CH with dyshormonogenesis.     

甲状腺过氧化物酶基因c.2268dupT突变与甲状腺结节的相关性研究

目的 探讨先天性甲状腺功能减退症(先天性甲减)患者及其家系成员发生甲状腺结节与突变位点的关系.方法 58例先天性甲减患者入选,提取外周血白细胞基因组DNA,根据甲状腺功能及超声检查结果选择靶基因.PCR扩增甲状腺过氧化物酶(TPO)、双氧化酶2(DOUX2)、双氧化酶成熟因子2(DOUXA2)、促甲状腺激素受体(TSHR)、钠/碘协同转运体(NIS)基因的所有外显子,对纯化PCR产物进行测序.发现突变后对其家系成员进行筛查.患者及家系成员行甲状腺功能和99mTc甲状腺扫描或超声检查,然后分析5个基因的突变位点与甲状腺结节的关系.结果 16例先证者为复合杂合子或纯合子,其中10例为TPO基因突变,含c.2268dupT突变者6例.37例家系成员为杂合突变,其中TPO基因突变25例.TPO基因c.2268dupT突变先证者及杂合携带者共20例,其中12例并发甲状腺结节.与其他所有突变位点组相比,c.2268dupT突变组的甲状腺结节患病率较高,差异有统计学意义(x2=13.545,P ＜0.01).结论 TPO基因c.2268dupT突变为高频突变,该突变携带者发生甲状腺结节危险性较高.     

Identification of a novel mutation in CYBB gene in a Chinese neonate with X-linked chronic granulomatous disease: A case report

Rationale:X-linked chronic granulomatous disease (X-CGD) is an X-linked recessive disorder of the Nicotinamide adenine dinucleotide phosphate oxidase system that can cause primary immunodeficiency. Mutations in the CYBB gene located in Xp21.1 were accounting for X-CGD disease. More than 600 mutations have been identified as the cause of X-CGD in various populations worldwide.Patient concerns and diagnosis:In this study, the proband suffered from elevated white blood cells (WBC, 23.65 × 109/L), mainly in neutral (16.4 × 109/L). The neutrophil oxidative index of the patient was 2.13, which was extremely low, whereas his mother was 69.0 (Ref >100). Next, next-generation sequencing of the primary immunodeficiency diseases -related gene panel was performed. One novel mutation was identified in the CYBB gene in the CGD case: c.55C>G in exon 2. The mutation was verified by Sanger sequencing. The mother of the patient was heterozygous for the c.55C>G mutation, and the father was normal. These mutations were not present in the 100 unrelated normal controls.Interventions and outcomes:The patient died from severe and uncontrollable pulmonary infection at 3 months of age.Lessons:The identification of these mutations in this study further expands the spectrum of known CYBB gene mutations and contributes to the genetic counseling and prenatal molecular diagnosis of X-CGD.     

Genetic linkage studies of thyroid peroxidase (TPO) gene in families with TPO deficiency.

We have conducted biochemical and genetic studies in five unrelated families (denoted A, C, R, P, and G), which included nine goitrous subjects (five borderline euthyroid and four hypothyroid) with complete (n = 6) or partial (n = 3) thyroid peroxidase (TPO) deficiency. Thyroid tissue was obtained from four subjects, respectively, in families A, C, and R. No iodide organification or iodide incorporation into protein was present in families A and C. The two affected siblings in family R had a low normal tissue thyroperoxidase activity. Using a 0.8-kilobase (kb) cDNA clone (pM5) encoding 30% of the cDNA of human TPO gene down-stream from basepair 730 and four restriction enzymes (TaqI, PstI, BglI, and BglII), we were unable to find any polymorphisms in family A. In another family (C) blood samples were obtained from only two family members, and consequently, it was not possible to determine linkage. DNA from families G, P, and C showed biallelic polymorphisms when digested with BglII, at 8.7 and 8.5 kb. In family R we detected two biallelic polymorphisms at 9.0 and 8.5 kb, and the 9.0-kb bands were clearly larger than 8.7-kb bands found in the other subjects. Also, there was an absence of a 4.0- to 3.9-kb band that may represent a partial gene deletion. With PstI-restricted DNA a possible deletion of 5.5-kb band was also present in affected siblings of family R. The logarithm of odds (Lod) score analyzed from the family with inbreeding (R) was compatible with linkage of disease and the TPO gene (Lod = 2.08). When this method was used with families G and P, the Lod score was inconsistent with linkage between disease and the TPO gene. These data suggest that the cause of TPO deficiency in these families is heterogeneous. However, the restriction fragment length polymorphism pattern of BglII-restricted DNA in the R family strongly suggests that a partial TPO gene deletion has occurred in this family.     

Total iodide organification defect: clinical and molecular characterization of an Italian family.

Thyroid peroxidase (TPO) deficiency is frequently involved in total iodide organification defects (TIOD). According to the recessive mode of inheritance, mutations are found in homozygous or in compound heterozygous states. However, a single heterozygous TPO mutation is reported in a high percentage (approximately 20%) of patients with typical TIOD phenotype. In the present study, the genetic and clinical evaluation of a TIOD family is reported. The propositus is an Italian girl with congenital hypothyroidism and positive perchlorate discharge test. Two TPO frameshift mutations were documented: a C deletion at 477 in exon 5, and a GGCC duplication at 1277 in exon 8. Unaffected family members, heterozygous for one of the two TPO mutations, were also studied in order to evaluate in vivo the functional activity of a single TPO allele. They have been found to have normal thyroid morphology and function with normal perchlorate test. In conclusion, the present study reports the clinical and molecular investigations in an Italian TIOD family. The results show that the TIOD phenotype in the propositus is associated to a compound heterozygous pattern, while a single TPO mutation does not significantly affect in vivo the efficiency of iodide organification. Therefore, extensive analyses of TPO gene and 2p25 locus are needed in the frequent TIOD cases in whom conventional investigations disclosed only one mutant allele.     

Presence of c.3956delC mutation in familial adenomatous polyposis patients from Brazil

AIM: To characterize APC gene mutations and correlate them with patient phenotypes in individuals diagnosed with familial adenomatous polyposis(FAP) in northern Brazil. METHODS: A total of 15 individuals diagnosed with FAP from 5 different families from the north of Brazil were analyzed in this study. In addition to patients with histopathological diagnosis of FAP,family members who had not developed the disease were also tested in order to identify mutations and for possible genetic counseling. All analyzed patients or their guardians signed a consent form approved by the Research Ethics Committee of the Jo?o de Barros Barreto University Hospital(Belem,Brazil). DNA extracted from the peripheral blood of a member of each of the affected families was subjected to direct sequencing. The proband of each family was sequenced to identify germline mutations using the Ion Torrent platform. To validate the detected mutations,Sanger sequencing was also performed. The samples from all patients were also tested for the identification of mutations by real-time quantitative polymerase chain reaction using the amplification refractory mutation system. RESULTS: Through interviews with relatives and a search of medical records,it was possible to construct genograms for three of the five families included in the study. All 15 patients from the five families with FAP exhibited mutations in the APC gene,and all mutations were detected in exon 15 of the APC gene. In addition to the patients with a histological diagnosis of FAP,family members without disease symptoms showed the mutation in the APC gene. In the present study,we detected two of the three most frequent germline mutations in the literature: the mutation at codon 1309 and the mutation at codon 1061. The presence of c.3956 del C mutation was found in all families from this study,and suggests that this mutation was introduced in the population of the State of Pará through ancestor immigration(i.e.,a de novo mutation that arose in one member belonging to this state from Brazil). CONCLUSION: Regardless of its origin,the c.3956 del C mutation is a strong candidate biomarker of this hereditary cancer syndrome in families of northern Brazil.     

Genetics of specific phenotypes of congenital hypothyroidism: a population-based approach.

Congenital hypothyroidism (CH) may cause severe and irreversible neurologic and developmental abnormalities when not recognized early. Many millions of newborns have now been screened and many thousands of patients with CH have been identified. Approximately 80%-85% have defects of thyroid gland development, while 15%-20% have congenital errors of thyroid hormone biosynthesis. An entire population screened for CH over a long period of time, was studied in the present report, using a population-based approach. In particular, two CH phenotypes, both presenting with in situ thyroid gland (patients with either goiter or with thyroid gland volume ranging from normal to hypoplasic) were analyzed. Mutations were searched in some of the most likely candidate genes: thyroperoxidase (TPO) in patients with CH goiter, Pax8 and thyrotropin receptor (TSHR) in the other group. In the former group (n = 8), four TPO gene mutations were identified in three patients. One patient was a compound heterozygous. In two cases an already described mutation (1277(insGGCC)) was present; in two other cases mutations not previously described (1996(G-->T) and 2295(G-->A)), which induced aminoacid variations with a Glu --> Stop and Val --> Ile changes, respectively, were identified. In all patients mutations were inherited from one of the parents. In the case of the compound heterozygous patient, one mutation was inherited from the mother (1277(insGGCC)) and the other from the father (1996(G-->T), Glu --> Stop). In the latter group (n = 8), a patient with a 16-base pair C(T)(13)CC deletion in TSHR gene intron 8, 42-bp distal to exon/intron 8 splice junction, was identified. No mutation was identified in Pax8 gene.     

Identification of Three Novel and One Known Mutation in the WFS1 Gene in Four Unrelated Turkish Families: The Role of Homozygosity Mapping in the Early Diagnosis

Objective:Bi-allelic mutations in the wolframin gene (WFS1) cause Wolfram syndrome 1 (WS1 or DIDMOAD) characterized by non-autoimmune diabetes mellitus, optic atrophy, diabetes insipidus, sensorineural deafness, urinary tract abnormalities, and neuropsychiatric disorders. Patients presenting with an incomplete phenotype of WS1 were evaluated using homozygosity mapping and subsequent whole-exome sequencing.Methods:Four unrelated consanguineous Turkish families, including seven affected children, and their unaffected parents and siblings were evaluated. Homozygosity mapping was performed, followed by whole-exome sequencing of WFS1. Mutations were classified according to results of “in silico” analyses, protein prediction, and functional consequences.Results:Homozygosity mapping confirmed shared homozygous regions on chromosome 4 (chr4p16.1) between the affected individuals, that was absent in their unaffected siblings. Exome sequencing identified three novel (c.1215T>A, c.554G>A, c.1525_1540dup) and one known (c.1522_1523delTA) mutations in WFS1. All mutations were predicted to cause stop codon leading to early termination of protein synthesis and complete loss-of-function. All patients were found to be homozygous for the change, with parents and other unaffected siblings being carriers.Conclusion:Our study expands the mutation spectrum of WSF1 mutations with three novel mutations. Homozygosity mapping may provide enrichment for molecular genetic analysis and early diagnosis of WS1 patients with incomplete phenotype, particularly in consanguineous pedigrees.     

Clinical and biochemical features associated with BCS1L mutation

Our study describes a novel phenotype in a series of nine Saudi patients with lactic acidosis, from four consanguineous families three of which are related. Detailed genetic studies including linkage, homozygosity mapping and targeted sequencing identified a causative mutation in the BCS1L gene. All affected members of the families have an identical mutation in this gene, mutations of which are recognized causes of Björnstad syndrome, GRACILE syndrome and a syndrome of neonatal tubulopathy, encephalopathy, and liver failure (MIM 606104) leading to isolated mitochondrial respiratory chain complex III deficiency. Here we report the appearance of a novel behavioral (five patients) and psychiatric (two patients) phenotype associated with a p.Gly129Arg BCS1L mutation, differing from the phenotype in a previously reported singleton patient with this mutation. The psychiatric symptoms emanated after childhood, initially as hypomania later evolving into intermittent psychosis. Neuroradiological findings included subtle white matter abnormalities, whilst muscle histopathology and respiratory chain studies confirmed respiratory chain dysfunction. The variable neuro-psychiatric manifestations and cortical visual dysfunction are most unusual and not reported associated with other BCS1L mutations. This report emphasizes the clinical heterogeneity associated with the mutation in BCS1L gene, even within the same family and we recommend that defects in this gene should be considered in the differential diagnosis of lactic acidosis with variable involvement of different organs.     

Variable clinical manifestation of a novel missense mutation in the alpha-tropomyosin (TPM1) gene in familial hypertrophic cardiomyopathy

OBJECTIVES: This study was initiated to identify the disease-causing genetic defect in a family with hypertrophic cardiomyopathy (HCM) and high incidence of sudden death. BACKGROUND: Familial hypertropic cardiomyopathy (FHC) is an autosomal dominant transmitted disorder that is genetically and clinically heterogeneous. Mutations in 11 genes have been associated with the pathogenesis of the disease. METHODS: We studied a large FHC family, first by linkage analysis, to identify the gene involved, and subsequently screened the gene, encoding alpha-tropomyosin (TPM1), for mutations by using single-strand conformation polymorphism and sequencing analysis. RESULTS: Twelve family members presented clinical features of HCM, five of whom died at young age, while others had only mild clinical features. Marker analysis showed linkage for the TPM1 gene on chromosome 15q22 (maximal logarithm of the odds score is 5.16, theta = 0); subsequently, a novel missense mutation (Glu62Gln) was identified. CONCLUSIONS: The novel mutation identified in TPM1 is associated with the clinical features of cardiac hypertrophy in all but one genetically affected member of this large family. The clinical data suggest a malignant phenotype at young age with a variable clinical manifestation and penetrance at older age. The Glu62Gln mutation is the sixth TPM1 mutation identified as the cause of FHC, indicating that mutations in this gene are very rare. This is the first reported amino acid substitution at the f-position within the coiled-coil structure of the tropomyosin protein.