Thymidine kinase 2 mutations in autosomal recessive progressive external ophthalmoplegia with multiple mitochondrial DNA deletions

Autosomal-inherited progressive external ophthalmoplegia (PEO) is an adult-onset disease characterized by the accumulation of multiple mitochondrial DNA (mtDNA) deletions in post-mitotic tissues. Mutations in six different genes have been described to cause the autosomal dominant form of the disease, but only mutations in the DNA polymerase gamma gene are known to cause autosomal recessive PEO (arPEO), leaving the genetic background of arPEO mostly unknown. Here we used whole-exome sequencing and identified compound heterozygous mutations, leading to two amino acid alterations R225W and a novel T230A in thymidine kinase 2 (TK2) in arPEO patients. TK2 is an enzyme of the mitochondrial nucleotide salvage pathway and its loss-of-function mutations have previously been shown to underlie the early-infantile myopathic form of mtDNA depletion syndrome (MDS). Our TK2 activity measurements of patient fibroblasts and mutant recombinant proteins show that the combination of the identified arPEO variants, R225W and T230A, leads to a significant reduction in TK2 activity, consistent with the late-onset phenotype, whereas homozygosity for R225W, previously associated with MDS, leads to near-total loss of activity. Our finding identifies a new genetic cause of arPEO with multiple mtDNA deletions. Furthermore, MDS and multiple mtDNA deletion disorders are manifestations of the same pathogenic pathways affecting mtDNA replication and repair, indicating that MDS-associated genes should be studied when searching for genetic background of PEO disorders.     

Molecular Genetic Analysis of SLC3A1 and SLC7A9 Genes in Czech and Slovak Cystinuric Patients

Cystinuria is a frequently inherited metabolic disorder in the Czech population (frequency 1/5,600) caused by a defect in the renal transport of cystine and dibasic amino acids (arginine, lysine and ornithine). The disease is characterized by increased urinary excretion of the amino acids and often leads to recurrent nephrolithiasis. Cystinuria is classified into two subtypes (type I and type non‐I). Type I is caused predominantly by mutations in the SLC3A1 gene (2p16.3), encoding heavy subunit (rBAT) of the heterodimeric transporter. Cystinuria non‐I type is caused by mutations in the SLC7A9 gene (19q13.1). In this study, we present results of molecular genetic analysis of the SLC3A1 and the SLC7A9 genes in 24 unrelated cystinuria families. Individual exons of the SLC3A1 and SLC7A9 genes were analyzed by direct sequencing. We found ten different mutations in the SLC3A1 gene including six novel ones: three missense mutations (G140R), D179Y and R365P), one splice site mutation (1137‐2A>G), one deletion (1515_1516delAA), and one nonsense mutation (Q119X). The most frequent mutation, M467T; was detected in 36% of all type I classified alleles. In the SLC7A9 gene we found six mutations including three new ones: one missense mutation (G319R), one insertion (611_612insA) and one deletion (205_206delTG). One patient was compound heterozygote for one SLC3A1 and one SLC7A9 mutation. Our results confirm that cystinuria is a heterogeneous disorder at the molecular level, and contribute to the understanding of the distribution and frequency of mutations causing cystinuria in the Caucasian population.     

Deoxyguanosine kinase mutations and combined deficiencies of the mitochondrial respiratory chain in patients with hepatic involvement

The activity of deoxyguanosine kinase (DGUOK), a mitochondrial enzyme involved in the anabolism of mitochondrial (mt) deoxyribonucleotides, governs the maintenance of the mtDNA. Deleterious mutations of the DGUOK gene are thus associated with mtDNA depletion and result in combined deficiencies of mtDNA-encoded respiratory chain enzymes. With the aim to estimate the prevalence of DGUOK mutations in a cohort of 30 patients with hepatocerebral disease and combined respiratory chain deficiencies, we studied the DGUOK gene and identified previously unreported mutations in five families. Two patients and their affected sibs, born to non-consanguineous parents, were homozygous for a missense mutation (M1T, and L250S, respectively). One patient presented a homozygous 4 pb insertion (796 insTGAT) and two other patients, and their affected sibs, were compound heterozygous (E165V/L266R and E211G/L266R, respectively). These findings allowed us to propose prenatal diagnosis in two families. In conclusion, we observed a high prevalence of DGUOK mutations (17%) in patients with hepatic involvement and combined respiratory chain deficiencies with hepatic involvement.     

Novel SLC5A2 Variants Contribute to Renal Glucosuria in Chinese Families: Abnormal Expression and Dysfunction of Variant SLC5A2

Familial renal glucosuria (FRG) is characterized by persistent glucosuria despite normal serum glucose and the absence of overt tubular dysfunction. Variants in solute carrier family 5 (sodium–glucose cotransporter), member 2 (SLC5A2) have been reported in FRG patients. However, the functional and expression‐related consequences of such variants have been scarcely investigated. In the current study, we studied five FRG families and identified six missense mutations, including four novel variants (c.1051T>C/.(C351R), c.1400T>C/p.(V467A), c.1420G>C/p.(A474P), c.1691G>A/p.(R564Q); RNA not analyzed) and two variants that had been previously reported (c.294C>A/p.(F98L), c.736C>T/p.(P246S); RNA not analyzed). The probands were either heterozygous or compound heterozygous for SLC5A2 variants and had glucosuria of 5.9%–19.6 g/day. Human 293 cells were transfected with plasmid constructs to study the expression and function of SLC5A2 variants in vitro. Western blotting revealed that the expression levels of SLC5A2–351R‐GFP, SLC5A2–467A‐GFP, SLC5A2–474P‐GFP, and SLC5A2–564Q‐GFP were significantly decreased compared with wild‐type SLC5A2‐GFP (37%–55%). Confocal microscopy revealed that three variants (c.1400T>C, c.1420G>C, c.1691G>A) resulted in a loss of the punctate membrane pattern typical of wild‐type SLC5A2. All variants had a significantly lower transport capacity in than the wild‐type control. The current study provides a starting point to further investigate the molecular mechanism of SLC5A2 in FRG families and provides functional clues for antidiabetes drugs.     

Identification of 13 novel mutations including a retrotransposal insertion in SLC25A13 gene and frequency of 30 mutations found in patients with citrin deficiency

Deficiency of citrin, liver-type mitochondrial aspartate-glutamate carrier, is an autosomal recessive disorder caused by mutations of the SLC25A13 gene on chromosome 7q21.3 and has two phenotypes: neonatal intrahepatic cholestatic hepatitis (NICCD) and adult-onset type II citrullinemia (CTLN2). So far, we have described 19 SLC25A13 mutations. Here, we report 13 novel SLC25A13 mutations (one insertion, two deletion, three splice site, two nonsense, and five missense) in patients with citrin deficiency from Japan, Israel, UK, and Czech Republic. Only R360X was detected in both Japanese and Caucasian. IVS16ins3kb identified in a Japanese CTLN2 family seems to be a retrotransposal insertion, as the inserted sequence (2,667-nt) showed an antisense strand of processed complementary DNA (cDNA) from a gene on chromosome 6 (C6orf68), and the repetitive sequence (17-nt) derived from SLC25A13 was found at both ends of the insert. All together, 30 different mutations found in 334 Japanese, 47 Chinese, 11 Korean, four Vietnamese and seven non-East Asian families have been summarized. In Japan, IVS16ins3kb was relatively frequent in 22 families, in addition to known mutations IVS11 + 1G > A, 851del4, IVS13 + 1G > A, and S225X in 189, 173, 48 and 30 families, respectively; 851del4 and IVS16ins3kb were found in all East Asian patients tested, suggesting that these mutations may have occurred very early in some area of East Asia.     

Pharmacological rescue of carnitine transport in primary carnitine deficiency

Primary carnitine deficiency is a recessive disorder caused by heterogeneous mutations in the SLC22A5 gene encoding the OCTN2 carnitine transporter. Here we extend mutational analysis to eight new families with this disorder. To determine the mechanism by which missense mutations impaired carnitine transport, the OCTN2 transporter was tagged with the green fluorescent protein and expressed in CHO cells. Analysis by confocal microscopy indicated that several missense mutants (M1I, R169W, T232 M, G242 V, S280F, R282Q, W283R, A301D, W351R, R399Q, T440 M, E452 K, and T468R) matured normally to the plasma membrane. By contrast, other mutations (including R19P, DeltaF22, R83L, S280F, P398L, Y447C, and A142S/R488 H) caused significant retention of the mutant OCTN2 transporter in the cytoplasm. Failed maturation to the plasma membrane is a common mechanism in disorders affecting membrane transporters/ion channels, including cystic fibrosis. To correct this defect, we tested whether drugs reducing the efficiency of protein degradation in the endoplasmic reticulum (ER) (phenylbutyrate, curcumin) or capable of binding the OCTN2 carnitine transporter (verapamil, quinidine) could improve carnitine transport. Prolonged incubation with phenylbutyrate, quinidine, and verapamil partially stimulated carnitine transport, while curcumin was ineffective. These results indicate that OCTN2 mutations can affect carnitine transport by impairing maturation of transporters to the plasma membrane. Pharmacological therapy can be effective in partially restoring activity of mutant transporters.     

Screening of SLC25A13 mutations in early and late onset patients with citrin deficiency and in the Japanese population: Identification of two novel mutations and establishment of multiple DNA diagnosis methods for nine mutations

We have recently identified SLC25A13 on chromosome 7q21.3 as the gene responsible for adult‐onset type II citrullinemia (CTLN2) and found seven mutations in the SLC25A13 gene of CTLN2 patients. Most recently, the SLC25A13 mutations have been detected in neonatal/infantile patients with a type of neonatal hepatitis associated with cholestasis (NICCD). In the present study, we identified a novel mutation, E601X, in the SLC25A13 gene and established multiple DNA diagnosis methods for eight mutations by using a genetic analyzer with GeneScan and the single primer extension procedure (SNaPshot). An additional novel missense mutation (variation), E601K, was detected by SNaPshot analysis and was indistinguishable from the mutation E601X detected by the PCR/RFLP method. Multiple DNA diagnoses for the nine mutations revealed that 100 (male/female: 70/30) out of 115 CTLN2 and 38 (14/24) out of 45 NICCD patients tested were homozygotes or compound heterozygotes. The frequency of homozygotes carrying SLC25A13 mutations in both alleles is estimated to be minimally 1 in 21,000 from carrier detection (18 in 1,315 individuals tested) in the Japanese population. The differences in the gender ratio and in mutation types between CTLN2 and NICCD patients are significant. It is, however, unknown whether all homozygotes with mutated SLC25A13 in both alleles suffer from NICCD, CTLN2, both, or neither. Hum Mutat 19:122–130, 2002. © 2002 Wiley‐Liss, Inc.     

Identification of sequence polymorphisms in two sulfation-related genes, PAPSS2 and SLC26A2, and an association analysis with knee osteoarthritis

Osteoarthritis (OA) is one of the most common musculoskeletal disorders and is characterized by degeneration of articular cartilage. Sulfation of extracellular ma-trix proteins in articular cartilage is an important step in maintaining normal cartilage metabolism. Two sulfation-related genes have been reported as the causal genes of severe chondrodysplasias: mutations in PAPSS2 (3′-phosphoadenosine 5′-phosphosulfate synthase 2) cause spondylo-epimetaphyseal dysplasia (SEMD), and mutations in SLC26A2 (solute carrier family 26, member 2) cause diastrophic dysplasia. Given their critical roles in cartilage metabolism and the severe phenotypes that result from mutations in these genes, we examined PAPSS2 and SLC26A2 as candidate susceptibility loci for OA. We identified sequence polymorphisms in the coding and core promoter regions of these genes and analyzed their potential association with knee OA within the Japanese population. Ten sequence polymorphisms were detected in PAPSS2 and five in SLC26A2. An association analysis showed suggestive association of one minor polymorphism in the promoter region of SLC26A2. This 4-bp adenine deletion allele, del4A, was over-represented in knee OA (P = 0.043, odds ratio = 3.43) and is thought to confer a minor susceptibility to knee OA within the Japanese population. Haplotype analysis showed no evidence of association with the two genes, however, excluding them as major susceptibility loci for knee OA. Received: May 7, 2001 / Accepted: June 21, 2001     

感音神经性耳聋患者大前庭导水管综合征相关SLC26A4基因IVS7-2A＞G的全序列分析

目的 对携带SLC26A4基因IVS7-2A＞G单杂合突变感音神经性耳聋患者进行 SLC26A4基因的全序列检测,以期发现除IVS7-2A＞G以外的其他突变.方法 应用直接测序法对80例携带IVS7-2A＞G单杂合突变的感音神经性耳聋患者进行SLC26A4基因进行全序列测序.结果 80例患者中47例发现另1个突变位点,其余33例未发现复合杂合突变,IVS7-2A＞G单杂合突变找到另外1个突变的比例为58.8%(47/80).发现了 3个新的突变,分别是5+2T＞A、14-2A＞G和1825del G,最为常见的5种突变为H723R(20%)、T410M(5%)、15+5G＞A(5%)、L676Q(5%)、N392Y(3.75%).第17外显子是突变发生种类最多的外显子.结论 SLC26A4基因IVS7-2A＞G单杂合突变者应该进行其他突变的筛查,SLC26A4基因复合突变可以解释部分的耳聋原因.     

Novel mutation in DGUOK in hepatocerebral mitochondrial DNA depletion syndrome associated with cystathioninuria

Mitochondrial depletion syndrome (MDS) refers to a heterogeneous group of mitochondrial disorders characterized by a reduction of the mtDNA copy number in affected tissues. Mutations in DGUOK encoding deoxyguanosine kinase (MIM 601465) cause the hepatocerebral form of MDS (MIM 251880). Cystathioninuria (MIM 219500) can result from mutations in CTH encoding cystathionine gamma lyase (MIM 607657) or can be a secondary finding in several diverse clinical conditions. We present three patients from two apparently unrelated old colony Mennonite families, each of whom had the hepatocerebral form of MDS together with cystathioninuria. Each affected child was homozygous for the novel DGUOK p.D255Y mutation, but had no CTH mutation, indicating that the hepatocerebral form of MDS might be associated with secondary cystathioninuria.     

Lack of TP53 and FMS gene mutations in children with myelodysplastic syndrome

Myelodysplastic syndromes (MDS) are rare disorders in children. Molecular mechanisms underlying MDS in children are not yet completely understood. Considering the role of FMS and TP53 gene mutations in adult MDS patients, we analyzed mutations of these genes in a cohort of 35 children with MDS. Single-strand conformation polymorphism polymerase chain reaction analysis performed on FMS codon 969 and TP53 exons 5-9 showed no mutations in the analyzed sequences. Our results suggest that molecular mechanisms of MDS evolution in children are different from those in adults.     

Thymidine kinase 2 (H126N) knockin mice show the essential role of balanced deoxynucleotide pools for mitochondrial DNA maintenance

Mitochondrial DNA (mtDNA) depletion syndrome (MDS), an autosomal recessive condition, is characterized by variable organ involvement with decreased mtDNA copy number and activities of respiratory chain enzymes in affected tissues. MtDNA depletion has been associated with mutations in nine autosomal genes, including thymidine kinase (TK2), which encodes a ubiquitous mitochondrial protein. To study the pathogenesis of TK2-deficiency, we generated mice harboring an H126N Tk2 mutation. Homozygous Tk2 mutant (Tk2(-/-)) mice developed rapidly progressive weakness after age 10 days and died between ages 2 and 3 weeks. Tk2(-/-) animals showed Tk2 deficiency, unbalanced dNTP pools, mtDNA depletion and defects of respiratory chain enzymes containing mtDNA-encoded subunits that were most prominent in the central nervous system. Histopathology revealed an encephalomyelopathy with prominent vacuolar changes in the anterior horn of the spinal cord. The H126N TK2 mouse is the first knock-in animal model of human MDS and demonstrates that the severity of TK2 deficiency in tissues may determine the organ-specific phenotype.     

Detection of uniparental isodisomy in autosomal recessive mitochondrial DNA depletion syndrome by high-density SNP array analysis

Mitochondrial DNA (mtDNA) depletion syndrome encompasses a heterogeneous group of disorders characterized by a reduction in the mtDNA copy number. We identified two patients with clinical presentations consistent with mtDNA depletion syndrome (MDS), who were subsequently found to have apparently homozygous point mutations in TYMP and DGUOK, two of the nine nuclear genes commonly associated with these disorders. Further sequence analyses of parents indicated that in each case only one parent; the mother of the first and the father of the second, was a heterozygous carrier of the mutation identified in the affected child. The presence of underlying deletions was ruled out by use of a custom target array comparative genomic hybridization (CGH) platform. A high-density single-nucleotide polymorphism (SNP) array analysis revealed that the first patient had a region of copy-neutral absence of heterozygosity (AOH) consistent with segmental isodisomy for an 11.3?Mb region at the long-arm terminus of chromosome 22 (including the TYMP gene), and the second patient had results consistent with complete isodisomy of chromosome 2 (where the DGUOK gene is located). The combined sequencing, array CGH and SNP array approaches have demonstrated the first cases of MDS due to uniparental isodisomy. This diagnostic scenario also demonstrates the necessity of comprehensive examination of the underlying molecular defects of an apparently homozygous mutation in order to provide patients and their families with the most accurate molecular diagnosis and genetic counseling.     

Analysis of slc19a2, on 1q23.3 encoding a thiamine transporter as a candidate gene for type 2 diabetes mellitus in pima indians

Mutations in the SLC19A2 gene cause thiamine-responsive megaloblastic anemia (TRMA) frequently combined with diabetes mellitus and deafness. Type 2 diabetes mellitus is heritable and a region on 1q21-q23 encompassing SLC19A2 was linked with the disease in Pima Indians and Caucasians. We therefore investigated this candidate gene in selected diabetic and nondiabetic Pimas and found no variants. We conclude that mutations in SLC19A2 do not contribute to type 2 diabetes in this population.     

Identification of fifteen novel mutations in the SLC12A3 gene encoding the Na-Cl Co-transporter in Italian patients with Gitelman syndrome

The SLC12A3 gene encodes the thiazide-sensitive Na-Cl co-transporter (NCCT) expressed in the apical membrane of the distal convoluted tubule of the kidney. Inactivating mutations of this gene are responsible for Gitelman syndrome (GS), a disorder inherited as an autosomal recessive trait. We searched for SLC12A3 gene mutations in 21 Italian patients with the clinical and biochemical features of GS (hypokalemia, hypomagnesemia, metabolic alkalosis, hypocalciuria, and the absence of nephrocalcinosis). All coding regions with their intron-exon boundaries were analyzed using PCR and SSCP techniques followed by sequencing analysis. We identified 21 different mutations evenly distributed throughout the gene without any mutation hot-spot. Fifteen are novel variants, including 12 missense mutations, one deletion, one deletion-insertion and one splice site mutation: R158Q, T163M, W172R, G316V, G374V, G463E, A464T, S615W, V677M, R852S, R958G, C985Y, 2114-2120delACCAAGT, 2144-2158delGCCTTCTACTCGGATinsTG, and 531-2A>G.     

Eleven novel mutations and clinical characteristics in seven Chinese patients with thiamine metabolism dysfunction syndrome

Thiamine metabolism dysfunction syndrome (THMD) comprises a group of clinically and genetically heterogeneous encephalopathies with autosomal recessive inheritance. Four genes, SLC19A3, SLC25A19, SLC19A2, and TPK1, are associated with this disorder. This study aimed to explore the clinical, biochemical and molecular characteristics of seven Chinese patients with THMD. Targeted next-generation sequencing of mitochondrial DNA and nuclear DNA was used to identify the causative mutations. The patients presented with subacute encephalopathy between the ages of 1–27 months. Brain magnetic resonance imaging (MRI) revealed abnormalities in the basal ganglia, indicating Leigh syndrome. Urine α-ketoglutarate in five patients was elevated. In four patients, five novel mutations (c.1276_1278delTAC, c.265A > C, c.197T > C, c.850T > C, whole gene deletion) were found in SLC19A3, which is associated with THMD2. In two patients, four novel mutations (c.194C > T, c.454C > A, c.481G > A, and c.550G > C) were identified in SLC25A19, supporting a diagnosis of THMD4. In one patient, two novel mutations (c.395T > C and c.614-1G > A) were detected in TPK1, which is indicative of THMD5. The patients received thiamine, biotin, and symptomatic therapy, upon which six patients demonstrated clinical improvement. Our findings expanded the phenotypic and genotypic spectrum of THMD, with eleven novel mutations identified in seven Chinese patients. Early diagnosis and treatment have a significant impact on prognosis.     

婴儿肝内胆汁淤积症SLC25A13基因突变分析

目的探讨SLC25A13基因突变在中国婴儿肝内胆汁淤积症患儿中的检出率,初步了解突变患儿血生化及氨基酸谱特征,肝脏活组织病理变化。方法2003年12月至2006年12月就诊于复旦大学附属儿科医院的婴儿肝内胆汁淤积症患儿,满足本研究入选条件者共115例进行了血氨基酸质谱分析,伴血浆瓜氨酸明显升高的患儿进行SLC25A13基因全部外显子及邻近序列测序,不伴血浆瓜氨酸明显升高的患儿进行SLC25A13基因常见突变851del4（突变Ⅰ）及突变1638ins23（突变Ⅲ）筛查,突变851del4采用实时荧光定量PCR双标记探针法检测,突变1638ins23采用PCR产物直接电泳法检测,对仅检出单个位点突变的筛查对象,继续进行其余已报道的10种突变位点检测。检测结果仍为单个杂合突变的对象进行SLC25A13基因所有外显子区及其邻近序列分析。对确诊突变患儿的临床表现、血生化及血氨基酸特征等进行分析。结果5例伴血瓜氨酸明显升高的患儿共检出突变4例,其中纯合突变851del4/851del41例,复合杂合突变851del4/1638ins231例,杂合突变851del42例;110例不伴血浆瓜氨酸明显升高患儿共检出突变6例,其中纯合突变851del4/851del41例,复合杂合突变851del4/1638ins231例,杂合突变851del44例。115例婴儿肝内胆汁淤积症患儿共检出SLC25A13基因突变10例,占8.7%。突变患儿血生化改变包括胆红素、γ-谷氨酰转移酶以及碱性磷酸酶等明显升高,AST升高较ALT明显。血串联质谱发现5例突变患儿有特征性氨基酸瓜氨酸、苏氨酸及蛋氨酸升高,另5例突变患儿并无血氨基酸改变。10例患儿中有7例行肝脏活组织病理学检查,4例有显著的脂肪变性。结论SLC25A13基因突变是中国婴儿肝内胆汁淤积症的重要原因之一。肝脏活组织病理、血生化及氨基酸谱等检查对诊断SLC25A13基因突变患儿有重要意义,但最终仍需通过基因检测确诊。     

Association of SLC26A4 muations with clinical features and thyroid function in deaf infants with enlarged vestibular aqueduct

Pendred syndrome and non-syndromic recessive deafness associated with enlarged vestibular aqueduct (NSRD with EVA) are caused by mutations in the SLC26A4 (PDS) gene. Unlike NSRD with EVA, Pendred syndrome is characterized by goiter, which may be present after early adulthood. However, the clinical diagnosis of these two disorders is difficult in deaf children. Expression of the SLC26A4 gene may be responsible for iodide transport in the thyroid as well as for formation and function of the inner ear. Here, we analyzed the SLC26A4 gene and performed thyroid function tests (FT3, FT4, TSH, and Thyroglobulin) on six congenitally deaf infants (mean age 2.7 years) with EVA. Mutation of the SLC26A4 gene was identified in five patients: four were compound heterozygous (H723R/919−2A>G, H723R/IVS15+5G>A, H723R/R581S, IVS7-2A>G/IVS8+1G>A), the fifth had a frameshift mutation (322delC). All the patients demonstrated an elevation of serum thyroglobulin level. FT3 level was elevated in four of the five patients. The patient who did not have a detectable gene mutation showed normal thyroid function. We conclude that the mutations in the SLC26A4 gene identified here are highly associated with high serum thyroglobulin levels in congenital and deafness infants. These mutations may be of value for the diagnosis of Pendred syndrome and NSRD with EVA.     

SLC25A13 gene mutations in Taiwanese patients with non-viral hepatocellular carcinoma

Mutations of the SLC25A13 gene, which encodes citrin, result in adult-onset type II citrullinemia (CTLN2). Because CTLN2 has been associated with hepatocellular carcinoma (HCC) and may be involved in hepatocarcinogenesis, the objective of this study was to assess the frequency of SLC25A13 mutations in patients with non-viral HCC. A retrospective review of 154 patients with HCC, who underwent total tumor resection from July 1998 to August 2005, was conducted. After exclusion of 137 patients infected with hepatitis B and/or C viruses, 17 patients were analyzed. Genomic DNA from stored tumor and normal hepatic samples was analyzed for the SLC25A13 gene mutation. In addition, the clinicopathological and histopathological features of patients with and without the SLC25A13 gene mutation were compared. The SLC25A13 mutation was observed in two patients (12%), and the carrier rate was approximately 1 in 8 patients. The IVS6+5G>A mutation was heterozygous in both normal hepatic and tumor tissues for case 1. On the other hand, the c.851del4 mutation was heterozygous in normal tissue but homozygous in tumor tissue for case 2. No significant differences in patient characteristics were observed. Further analyses of patients with SLC25A13 gene mutations may elucidate the relationship between the citrin gene and susceptibility of HCC.