Molecular characterization of WFS1 in an Iranian family with Wolfram syndrome reveals a novel frameshift mutation associated with early symptoms

Wolfram syndrome (WS) is a rare autosomal recessive neurodegenerative disorder that represents a likely source of childhood diabetes especially among countries in the consanguinity belt. The main responsible gene is WFS1 for which over one hundred mutations have been reported from different ethnic groups. The aim of this study was to identify the molecular etiology of WS and to perform a possible genotype–phenotype correlation in Iranian kindred.     

Comorbidity of GJB2 and WFS1 mutations in one family

It is rarely reported that two distinct genetic mutations affecting hearing have been found in one family. We report on a family exhibiting comorbid mutation of GJB2 and WFS1. A four-generation Japanese family with autosomal dominant sensorineural hearing loss was studied. In 7 of the 24 family members, audiometric evaluations and genetic analysis were performed. We detected A-to-C nucleotide transversion (c.2576G>C) in exon 8 of WFS1 that was predicted to result in an arginine-to-proline substitution at codon 859 (R859P), G-to-A transition (c.109G>A) in exon 2 of GJB2 that was predicted to result in a valine-to-isoleucine substitution at codon 37 (V37I), and C-to-T transition (c.427C>T) in exon 2 of GJB2 that was predicted to result in an arginine-to-tryptophan substitution at codon 143 (R143W). Two individuals who had heterozygosity of GJB2 mutations and heterozygosity of WFS1 mutations showed low-frequency hearing loss. One individual who had homozygosity of GJB2 mutation without WFS1 mutation had moderate, gradual high tone hearing loss. On the other hand, a moderate flat loss configuration was seen in one individual who had compound heterozygosity of GJB2 and heterozygosity of WFS1 mutations. Our results indicate that the individual who has both GJB2 and WFS1 mutations can show GJB2 phenotype.     

Novel mutations of endothelin-B receptor gene in Pakistani patients with Waardenburg syndrome

Mutations in EDNRB gene have been reported to cause Waardenburg-Shah syndrome (WS4) in humans. We investigated 17 patients with WS4 for identification of mutations in EDNRB gene using PCR and direct sequencing technique. Four genomic mutations were detected in four patients; a G to C transversion in codon 335 (S335C) in exon 5 and a transition of T to C in codon (S361L) in exon 5, a transition of A to G in codon 277 (L277L) in exon 4, a non coding transversion of T to A at −30 nucleotide position of exon 5. None of these mutations were found in controls. One of the patients harbored two novel mutations (S335C, S361L) in exon 5 and one in Intronic region (−30exon5 A>G). All of the mutations were homozygous and novel except the mutation observed in exon 4. In this study, we have identified 3 novel mutations in EDNRB gene associated with WS4 in Pakistani patients.     

Wolfram syndrome: new mutations, different phenotype

Background

Wolfram Syndrome (WS) is an autosomal recessive neurodegenerative disorder characterized by Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy, and Deafness identified by the acronym “DIDMOAD”. The WS gene, WFS1, encodes a transmembrane protein called Wolframin, which recent evidence suggests may serve as a novel endoplasmic reticulum calcium channel in pancreatic β-cells and neurons. WS is a rare disease, with an estimated prevalence of 1/550.000 children, with a carrier frequency of 1/354.The aim of our study was to determine the genotype of WS patients in order to establish a genotype/phenotype correlation.

Methodology/Principal Findings

We clinically evaluated 9 young patients from 9 unrelated families (6 males, 3 females). Basic criteria for WS clinical diagnosis were coexistence of insulin-treated diabetes mellitus and optic atrophy occurring before 15 years of age. Genetic analysis for WFS1 was performed by direct sequencing.Molecular sequencing revealed 5 heterozygous compound and 3 homozygous mutations. All of them were located in exon 8, except one in exon 4. In one proband only an heterozygous mutation (A684V) was found. Two new variants c.2663 C>A and c.1381 A>C were detected.

Conclusions/Significance

Our study increases the spectrum of WFS1 mutations with two novel variants. The male patient carrying the compound mutation [c.1060_1062delTTC]+[c.2663 C>A] showed the most severe phenotype: diabetes mellitus, optic atrophy (visual acuity 5/10), deafness with deep auditory bilaterally 8000 Hz, diabetes insipidus associated to reduced volume of posterior pituitary and pons. He died in bed at the age of 13 years. The other patient carrying the compound mutation [c.409_424dup16]+[c.1381 A>C] showed a less severe phenotype (DM, OA).     

Identification of two novel mutations in the first Sicilian APECED patient with no R203X mutation in AIRE gene and review of Italian APECED genotypes

Aims of the present study are: 1) to report an additional Sicilian patient with autoimmune polyendocrinopathy-candidiasis-ectodermal-dystrophy (APECED), whose genotypic features are original, in that she is the first APECED patient with three coexisting mutations of Autoimmune Regulator (AIRE) gene, two of which had never been reported to date; 2) to review the genotypic epidemiology of APECED in Italy, in order to underline the great genetic heterogeneity of this disorder in Italian patients. Both the novel mutations of our new patient, named S107C and Q108fs respectively, were detected on exon 3 and were inherited by the mother, whereas the third one (T16M) was inherited by the father. Phenotypically, the present case is quite characteristic, in that she exhibited a classical clinical picture, with no original features. Conclusions: a) this is the seventh Sicilian APECED patient identified to date, and the first one with no R203X mutation; b) our data confirm that distribution of mutations may considerably vary according to different geographical distribution, within the same country, thus suggesting a potential founder effect.     

A novel mutation in MID1 in a patient with X-linked Opitz G/BBB syndrome

Opitz G/BBB syndrome (OS) is a genetically heterogeneous disease. We report on an OS patient with a novel inherited mutation in MID1. Metaphase analysis showed a normal male karyotype. Array CGH revealed a maternally inherited duplication at Xp22.31 (6,467,203–7,992,261, hg18), the size was estimated to 1.5 Mb. Sequence analysis of the MID1 coding region revealed a novel missense mutation in exon 8 (c.1561C>T/p. R521C) which resulted in an ammonia acid substitution (R521C) in the PRX domain of the MID1 protein. The mutation was inherited from unaffected grandmother and mildly affected mother. Prenatal diagnosis was performed for the third pregnancy after identification of the causative mutation in the family. The third fetus was found to be a female carrier. Postnatal follow-up at 2-month-old showed normal phenotype. In conclusion, we reported a familial OS patient with a novel mutation in exon 8 which provided another evidence for that mutation clustered in C-terminal domain of MID1. The newly identified mutation in our patient expands mutation spectrum in MID1 gene.     

Identification of two novel missense WFS1 mutations, H696Y and R703H,in patients with non-syndromic low-frequency sensorineural hearing loss

Non-syndromic low-frequency sensorineural hearing loss (LFSNHL) is an unusual type of hearing loss in which frequencies ≤2000 Hz predominantly are affected. To date, different mutations in two genes, DIAPH1 and WFSI, have been found to be associated with LFSNHL.Here, we report a five-generation Chinese family with postlingual and progressive LFSNHL. We mapped the disease locus to a 2.5 Mb region on chromosome 4p16 between markers SNP_A-2167174 and D4S431, overlapping with the DFNA6/14/38 locus. Sequencing of candidate gene revealed a heterozygous c.2086C＞T substitution in exon 8 of WFS1, leading to p. H696Y substitution at the C-terminus of Wolframin (WFS1).In addition, we performed mutational screening of WFS1 in 37 sporadic patients, 7-50 years of age, with LFSNHL. We detected a heterozygous c.2108G＞A substitution in exon 8 of WFS1, leading to p. R703H substitution in a patient. The H696 and R703 in WFS1 are highly conserved across species, including human, orangutan, rat, mouse, and frog (Xenopus). Sequence analysis demonstrated the absence of c.2086C＞T or c.2108G＞A substitutions in the WFS1 genes among 200 unrelated control subjects of Chinese background, supporting the hypothesis that they represent causative mutations, and not rare polymorphisms. Our data provide additional molecular and clinical information for establishing a better genotype-phenotype correlation for LFSNHL.     

Novel Mutations in the Human HPRT Gene

Inherited mutation of a purine salvage enzyme, hypoxanthine guanine phosphoribosyltransferase (HPRT), gives rise to Lesch-Nyhan Syndrome (LNS) or HPRT-related gout. Here, we report five novel independent mutations in the coding region of the HPRT gene from five unrelated male patients manifesting different clinical phenotypes associated with LNS: exon 2: c.133A > G, p.45R > G; c.35A > C, p.12D > A; c.88delG; exon 7: c.530A > T, p.177D > V; and c.318 + 1G > C: IVS3 + 1G > C splice site mutation.     

Clinical and Molecular Genetic Analysis of 19 Wolfram Syndrome Kindreds Demonstrating a Wide Spectrum of Mutations in WFS1

Wolfram syndrome is an autosomal recessive neurodegenerative disorder characterized by juvenile-onset diabetes mellitus and progressive optic atrophy. mtDNA deletions have been described, and a gene (WFS1) recently has been identified, on chromosome 4p16, encoding a predicted 890 amino acid transmembrane protein. Direct DNA sequencing was done to screen the entire coding region of the WFS1 gene in 30 patients from 19 British kindreds with Wolfram syndrome. DNA was also screened for structural rearrangements (deletions and duplications) and point mutations in mtDNA. No pathogenic mtDNA mutations were found in our cohort. We identified 24 mutations in the WFS1 gene: 8 nonsense mutations, 8 missense mutations, 3 in-frame deletions, 1 in-frame insertion, and 4 frameshift mutations. Of these, 23 were novel mutations, and most occurred in exon 8. The majority of patients were compound heterozygotes for two mutations, and there was no common founder mutation. The data were also analyzed for genotype-phenotype relationships. Although some interesting cases were noted, consideration of the small sample size and frequency of each mutation indicated no clear-cut correlations between any of the observed mutations and disease severity. There were no obvious mutation hot spots or clusters. Hence, molecular screening for Wolfram syndrome in affected families and for Wolfram syndrome-carrier status in subjects with psychiatric disorders or diabetes mellitus will require complete analysis of exon 8 and upstream exons.     

Biochemical and genetic studies of four patients with pyruvate dehydrogenase E1α deficiency

We report studies of four patients with pyruvate dehydrogenase complex (PDH) deficiency caused by mutations in the E1α subunit. Two unrelated male patients presented with Leigh syndrome and a R263G missense mutation in exon 8. This mutation has previously been described in males with the same phenotype. The two other patients had different novel mutations: (1) an 8-bp deletion at the C-terminus (exon 11) was found in one allele of a young girl suffering from microcephaly and (2) a C88S missense mutation (exon 3) in a boy who only presented with motor neuropathy. These mutations were not found in the mothers of any of the four cases. Immunoblot analysis revealed decreased immunoreactivity for the E1α and E1β subunits in three out of the four patients. These findings confirm that: (1) PDH deficiencies are genetically heterogeneous, (2) the R263G mutation is more frequent in male cases than are other mutations and this amino acid is a hot spot for gene mutations, (3) the last eight amino acids may be important for the conformation of the tetrameric E1-PDH enzyme, and (4) the amino acids at positions 88, 263 and 382–387 are essential for the linking of the α subunit with the β subunit and for the activity of the holoenzyme. Received: 28 October 1996 / Revised: 13 January 1997     

Significant expressivity of Wolfram syndrome: phenotypic assessment of two known and one novel mutation in the WFS1 gene in three Iranian families

Wolfram syndrome also known as DIDMOAD (Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy, and Deafness) is a rare neurodegenerative autosomal recessive disorder. There is evidence of variable expressivity both in patients and heterozygous carriers. In this study, we describe three Persian Wolfram syndrome families with differences in the age of onset, signs and symptoms of the disease. We clinically evaluated affected families for verifying WS clinical diagnosis. After linkage analysis via 5 STR markers, molecular analysis for WFS1 was performed by direct sequencing for patients and available family members. Three homozygous mutations were identified including c.1885 C>T, c.2205C>A both in exon 8 and c.460+1G>A in intron 4. The mutation c.2205C>A was found to be novel. We report interesting phenotype-genotype correlations: homozygous c.1885C>T and c.2205C>A variants were correlated with quite different disease severity and onset in the siblings. We report a rare case of WS with homozygous c.1885C>T who is married and has a healthy child. c.460+1G>A showed a possible partial dominant inheritance put forth by a heterozygous parent showing partial WS symptoms while her daughter displayed typical WS symptoms. Due to variable expressivity, detailed clinical examination and molecular diagnostics should be used to confirm WS and a more exact recurrence risk data.     

Missense variations of the gene responsible for Wolfram syndrome (WFS1/wolframin) in Japanese: possible contribution of the Arg456His mutation to type 1 diabetes as a nonautoimmune genetic basis

Recently, a novel gene for a putative transmembrane protein (WFS1/wolframin) was found to be mutated in patients with Wolfram syndrome or DI-DM-OA-D (diabetes insipidus, diabetes mellitus, optic atrophy, and deafness) syndrome. It is suggested that the WFS1 protein is important in the survival of islet beta-cells. We studied the WFS1 gene in a Japanese population to assess its possible role in common type 1 diabetes. Mutation screening revealed four missense mutations; R456H, G576S, H611R, and I720V. By genetic association studies of 185 type 1 diabetes patients and 380 control subjects, we found that R456H was significantly increased in the type 1 diabetes group compared to the control group (P = 0.0005); H611R and I720V were also significantly increased with weaker significance. Furthermore, in patients with the R456H mutation, type 1 diabetes-resistant HLA-DRB1 alleles (DRB1*0406, 1501, and 1502) were significantly increased compared to mutation-negative patients while susceptible DRB1*0901 was significantly decreased. Frequencies of autoimmunity characteristics (ICA or GAD-Ab positiveness and combination of autoimmune thyroid disease) were decreased in the R456H-positive patients compared to the R456H-negative patients. These data suggest that the WFS1 gene may have a role in the development of common type 1 diabetes as a nonautoimmune genetic basis.     

Novel mutations in the human HPRT gene

Inherited mutation of a purine salvage enzyme, hypoxanthine guanine phosphoribosyltransferase (HPRT), gives rise to Lesch-Nyhan Syndrome (LNS) or HPRT-related gout. Here, we report five novel independent mutations in the coding region of the HPRT gene from five unrelated male patients manifesting different clinical phenotypes associated with LNS: exon 2: c.133A > G, p.45R > G; c.35A > C, p.12D > A; c.88delG; exon 7: c.530A > T, p.177D > V; and c.318 + 1G > C: IVS3 + 1G > C splice site mutation.     

Leigh syndrome associated with mitochondrial complex I deficiency due to novel mutations In NDUFV1 and NDUFS2

Leigh syndrome (LS) is a progressive neurodegenerative disease caused by either mitochondrial or nuclear DNA mutations resulting in dysfunctional mitochondrial energy metabolism. Mutations in genes encoding for subunits of the respiratory chain or assembly factors of respiratory chain complexes are often documented in LS cases. Nicotinamide adenine dinucleotide (NADH):ubiquinone oxidoreductase (complex I) enzyme deficiencies account for a significant proportion of mitochondrial disorders, including LS. In an attempt to expand the repertoire of known mutations accounting for LS, we describe the clinical, radiological, biochemical and molecular data of six patients with LS found to have novel mutations in two complex I subunits (NDUFV1 and NDUFS2). Two siblings were homozygous for the previously undescribed R386C mutation in NDUFV1, one patient was a compound heterozygote for the R386C mutation in NDUFV1 and a frameshift mutation in the same gene, one patient was a compound heterozygote for the R88G and R199P mutations in NDUFV1, and two siblings were compound heterozygotes for an undescribed E104A mutation in NDUFS2. After the novel mutations were identified, we employed prediction models using protein conservation analysis (SIFT, PolyPhen and UCSC genome browser) to determine pathogenicity. The R386C, R88G, R199P, and E104A mutations were found to be likely pathogenic, and thus presumably account for the LS phenotype. This case series broadens our understanding of the etiology of LS by identifying new molecular defects that can result in complex I deficiency and may assist in targeted diagnostics and/or prenatal diagnosis of LS in the future.     

Waardenburg综合征Ⅱ型患者MITF基因突变分析

Waardenburg综合征(WS)是临床上常见的常染色体显性遗传性耳聋综合征, MITF基因突变与部分Waardenburg 综合征Ⅱ型(WS2)病例的发病有关。MITF属于碱性螺旋-环-螺旋亮氨酸拉链转录因子家族, 能调节酪氨酸酶基因, 参与黑色素细胞的分化。文章报道了1个携带MITF基因点突变的3代Waardenburg综合征Ⅱ型中国家系。先证者表现为先天性重度感音神经性聋、虹膜异色、面部雀斑; 其他家系成员除一名仅表现为先天性耳聋外, 均表现为颜面、上肢雀斑和/或早白发。患者可检测到c.639delA杂合突变, 该突变在MITF基因第7外显子上产生了终止密码子(p.I220X), 突变产生的截短的MITF蛋白没有DNA结合活性。该突变是WS2病例中第3个位于MITF第7外显子的突变, 尚未见报道。该突变与已报道的位于第7外显子其他两个突变仅相差1个碱基, 氨基酸改变十分相似, 但在表型上有显著差别, 提示遗传背景对WS临床表型有重要影响。     

Identification of Novel Mutations in the Human HPRT Gene

Inherited mutation of the purine salvage enzyme, hypoxanthine guanine phosphoribosyltransferase (HPRT) gives rise to Lesch–Nyhan syndrome (LNS) or Lesch–Nyhan variants (LNVs). We report three novel independent mutations in the coding region of HPRT gene: exon 3: c.141delA, p.D47fs53X; exon 5: c.400G>A, p.E134K; exon 7: c.499A>G, p.R167G from three LNS affected male patients.     

Novel missense mutations outside the allosteric domain of glutamate dehydrogenase are prevalent in European patients with the congenital hyperinsulinism-hyperammonemia syndrome

The hyperinsulinism-hyperammonemia syndrome (HHS) has been shown to result from 'gain-of-function' mutations of the glutamate dehydrogenase (GlDH) gene, GLUD1. In the original report, all mutations were found in a narrow range of 27 base pairs within exons 11 and 12 which predicted an effect on the presumed allosteric domain of the enzyme and all these mutations were associated by a diminished inhibitory effect of guanosine triphosphate (GTP) on GlDH activity. We have investigated 14 patients from seven European families with mild hyperinsulinism. In four families, more than one member was affected. In eight cases hyperammonemia was documented, and eight cases had signs of significant leucine sensitivity. In one of the families, a novel heterozygous missense mutation in exon 6 [c.833C>T (R221C)] was detected, and in all other cases from six unrelated families the novel heterozygous missense mutation c.978G>A (R269H) was found in exon 7. When GIDH activity was measured in lymphocytes isolated from affected patients, both mutations were shown to result in a normal basal activity but a diminished sensitivity to GTP. It is the first time that this effect is reported for mutations located in the presumed catalytic site and outside the GTP allosteric domain of the enzyme. The observation of the high prevalence of the exon 7 mutation both in familial and sporadic cases of HHS suggests a mutation hot spot and justifies a mutation screening for this novel mutation by mismatch PCR-based restriction enzyme digestion in patients with hyperinsulinism.     

A novel mutation (R122Q) in the cathepsin K gene in a Chinese child with Pyknodysostosis

Background

Pyknodysostosis (OMIM 265800) is a rare, autosomal recessive sclerosing skeletal dysplasia as a consequence of the diminished capacity of osteoclasts to degrade organic bone matrix. Pyknodysostosis is caused by mutation in the cathepsin K (CTSK) gene. Up to date, 34 different CTSK mutations have been identified in patients with Pyknodysostosis; however, only one mutation was previously identified in a Chinese patient. The objective of this study was to characterize the clinical manifestations and features of Pyknodysostosis and identify the mutation of the causative gene in a Chinese family with Pyknodysostosis.

Methods

We investigated a non-consanguineous Chinese family in which an 11-year-old child was affected with Pyknodysostosis. Altogether, 203 persons, including the affected individual, his parents and 200 healthy donors, were recruited and genomic DNA was extracted. All 8 exons of the CTSK gene, including the exon–intron boundaries, were amplified and sequenced directly.

Results

The proband displayed a novel homozygous missense mutation c.365G>A in exon 4 of the CTSK gene. This mutation leads to the substitution of the arginine at position 122 by glutamine (R122Q) in cathepsin K. The parents were heterozygous for this gene mutation, and the mutation was not found in the 200 unrelated controls.

Conclusion

Our study suggests that the novel missense mutation c.365G>A (R122Q) in exon 4 of CTSK gene was responsible for Pyknodysostosis in the Chinese family.