A novel homozygous nonsense mutations E135* in the type II 3beta-hydroxysteroid dehydrogenase gene in a girl with salt-losing congenital adrenal hyperplasia. Mutations in brief no. 168. Online

Mutations in the 3beta-hydroxysteroid dehydrogenase (3beta-HSD) type II gene have been reported in a small number of affected females. We report a 46,XX girl born to consanguineous parents from Chile. At birth, she had normal but hyperpigmented female external genitalia. At 60 days she presented salt loss. At 20 months, the diagnosis of classic salt-losing 3beta-HSD deficiency was made based on an elevated serum 17-hydroxpregnenolone concentration and a high 17 hydroxypregnenolone/17-hydroxyprogesterone ratio. Genomic DNA was amplified by PCR and screened for mutations by denaturing gradient gel electrophoresis and directly sequenced. A novel homozygous E135* mutation was found in the 3beta-HSD type II gene of the patient while her parents were heterozygotes. This novel nonsense homozygous E135* mutation led to encode a predicted truncated 134 amino acid protein instead of the native 371 amino acid 3beta-HSD type II protein. This predicted product is consistent with the severe 3beta-HSD deficiency in this girl.     

Congenital adrenal hyperplasia caused by a novel homozygous frameshift mutation 273{Delta}AA in type II 3{beta}-hydroxysteroid dehydrogenase gene (HSD3B2) in three male patients of Afghan/Pakistani origin

Classical 3ß-hydroxysterold dehydrogenase (3ß-HSD)deficiency is an autosomal recessive form of congenital adrenalhyperplasia caused by mutations in the type II 3ß-HSD(HSD3B2) gene. The sequence of the type II 3ß-HSDgene was determined by direct sequencing of asymmetric PCR productsin three male infants suffering from a severe salt-losing formof 3ß-HSD deficiency and belonging to three familiesoriginating from Afghanistan and Pakistan. The three patientswere homozygous for the frameshift mutation 273     

Root dentin anomaly and a PLG mutation

We report a Thai girl affected with plasminogen deficiency, Type I. Ligneous conjunctivitis was first observed when she was one-month-old. The newly recognized findings include tapered incisor roots as a result of thin root dentin, generalized short tooth roots, and mandibular prognathism. Mutation analysis of PLG demonstrated homozygous c.1193G>A missense mutation. The parents were heterozygous for c.1193G>A mutation. The c.1193G>A mutation is novel and predicted to cause amino acid substitution p.Cys398Tyr. Thin root dentin in the patient who was affected with PLG mutation and immunolocalization of Plg during early root development in mice imply the role of plasminogen in root dentin formation.     

Cloning of the human MCCA and MCCB genes and mutations therein reveal the molecular cause of 3-methylcrotonyl-CoA: carboxylase deficiency.

3-Methylcrotonyl-CoA: carboxylase (EC 6.4.1.4; MCC) deficiency is an inborn error of the leucine degradation pathway (MIM *210200) characterized by increased urinary excretion of 3-hydroxyisovaleric acid and 3-methylcrotonylglycine. The clinical phenotypes are highly variable ranging from asymptomatic to profound metabolic acidosis and death in infancy. Sequence similarity with Glycine max and Arabidopsis thaliana genes encoding the two subunits of MCC permitted us to clone the cDNAs encoding the alpha- and beta-subunits of human MCC. The 2580 bp MCCA cDNA encodes the 725 amino acid biotin-containing alpha-subunit. The MCCA gene is located on chromosome 3q26-q28 and consists of 19 exons. The 2304 bp MCCB cDNA encodes the non-biotin-containing beta-subunit of 563 amino acids. The MCCB gene is located on chromosome 5q13 and consists of 17 exons. We have sequenced both genes in four patients with isolated biotin-unresponsive deficiency of MCC. In two of them we found mutations in the MCCA gene. Compound heterozygosity for a missense mutation (S535F) and a nonsense mutation (V694X) were identified in one patient. One heterozygous mutation (S535F) was found in another patient. The remaining two patients had mutations in the MCCB gene. One consanguineous patient was homozygous for a missense mutation (R268T). In the other we identified a missense mutation in one allele (E99Q) and allelic loss of the other. Mutations were correlated with an almost total lack of enzyme activity in fibroblasts. These data provide evidence that human MCC deficiency is caused by mutations in either the MCCA or MCCB gene.     

Homozygous mutation (A228T) in the 5α-reductase type 2 gene in a boy with 5α-reductase deficiency: Genotype–phenotype correlations

The molecular basis of a patient with 5α-reductase deficiency was investigated in this study. This disease is a rare form of male pseudohermaphroditism with virilization during puberty. The child was raised as a girl, but had a male gender identity early in life. The diagnosis was set at the age of 13 years when the virilization process began. Hypospadias repair was performed and he changed to a male gender. DNA sequence analysis disclosed a homozygous mutation in exon 4 of the 5α-reductase type 2 gene, alanine 228 for threonine. The heterozygous parents are first cousins of Pakistani origin. Am. J. Med. Genet. 80:269–272, 1998. © 1998 Wiley-Liss, Inc.     

ACTH receptor mutation in a girl with familial glucocorticoid deficiency

Familial glucocorticoid deficiency (FGD) has long been recognised as a clinical entity, but molecular studies have so far been performed in only a few individuals. We describe a girl born to consanguineous Pakistani parents with clinical and biochemical features of FGD who is homozygous for the R146H mutation of the adrenocorticotropic hormone (ACTH) receptor gene. This mutation creates a new restriction enzyme site in the ACTH receptor gene, allowing accurate characterisation of the mutation without DNA sequencing. Our patient is the third child reported to be homozygous for the R146H mutation. Interestingly, she has a tall stature, a clinical finding reported in several children who have ACTH insufficiency and mutations of the ACTH receptor gene. We suggest that mutation analysis of the ACTH receptor gene be considered in children with clinical features of FGD and tall stature.     

A novel 13-bp deletion in exon 1 of CYP21 gene causing severe congenital adrenal hyperplasia.

Congenital adrenal hyperplasia (CAH) is a common autosomal recessive disorder mainly caused by defects in the steroid 21-hydroxylase gene (CYP21). In most cases, this defect is the result of gene conversion events between the functional CYP21 gene and the adjacent inactive pseudogene (CYP21P). Previous screening for mutations of 21-hydroxylase gene in 51 unrelated Tunisian CAH patients revealed 4 novel mutations that have not been reported to occur in the CYP21P pseudogene. The present paper describes the fifth new small 13-bp deletion in exon 1 found after sequencing the CYP21 gene of a Tunisian patient suffering from the salt-wasting form of CAH. The patient is a girl born to consanguineous parents; she is homozygous for a novel deletion. The 13-bp deletion causes a stop codon at amino acid 47, which is likely to result in an enzyme with no activity. Both parents are heterozygous for the small deletion as confirmed by nested PCR method. This novel mutation has not been reported to occur in the CYP21P pseudogene, indicating a casual mutagenic event rather than a conversion one.     

Homozygous Gly555Glu mutation in the nuclear-encoded 70 kDa flavoprotein gene causes instability of the respiratory chain complex II

A homozygous mutation in the flavoprotein (Fp) gene associated with complex II deficiency was demonstrated in a patient with consanguineous parents. She succumbed at 5(1/2) months of age following a respiratory infection. The c1664G-->A transition detected, predicted the substitution of the small uncharged glycine at position 555 by glutamic acid. Her clinical course was at variance with the Leigh syndrome in three previously reported patients due to Fp gene mutations. In this proband, CRM for flavoprotein as well as iron-containing protein (Ip) was decreased, CRM for the entire complex II (130 kDa) being reduced even more. This observation prompts speculation of a labile interaction between Ip and Fp polypeptides and of a key role of the amino acid at position 555 in the interacting domain.     

Two CPT2 mutations in three Japanese patients with carnitine palmitoyltransferase II deficiency: Functional analysis and association with polymorphic haplotypes and two clinical phenotypes

Carnitine palmitoyltransferase II (CPT II) deficiency manifests as two different clinical phenotypes: a muscular form and a hepatic form. We have investigated three nonconsanguineous Japanese patients with CPT II deficiency. Molecular analysis revealed two missense mutations, a glutamate (174)-to-lysine substitution (E174K) and a phenylalanine (383)-to-tyrosine substitution (F383Y) in the CPT II cDNA. Transfection experiments in COS-1 cells demonstrated that the two mutations markedly decreased the catalytic activity of mutant CPT II. Case 1 (hepatic form) was homozygous for the F383Y mutation, whereas case 3 (muscular form) was homozygous for the E174K mutation. Case 2 and her brother, who were compound heterozygotes for E174K and F383Y, exhibited the hepatic phenotype. We also identified a novel polymorphism in the CPT2 gene, a phenylalanine (352)-to-cysteine substitution (F352C), which did not alter CPT II activity in transfected cells. It was present in 21 out of 100 normal alleles in the Japanese population, but absent in Caucasian populations. Genotyping with the F352C polymorphism and the two previously reported polymorphisms, V368I and M647V, allowed normal Japanese alleles to be classified into five haplotypes. In all three families with CPT II deficiency, the E174K mutation resided only on the F1V1M1 allele, whereas the F383Y mutation was observed on the F2V2M1 allele, suggesting a single origin for each mutation. Hum Mutat 11:377–386, 1998. © 1998 Wiley-Liss, Inc.     

Sequencing of two new HLA class II alleles: DRB3*0218 and DQB1*030202

Two novel human leukocyte antigen (HLA) class II alleles for DRB3 and DQB1 genes detected in Caucasoid Spanish individuals are described: DRB3*0218 and DQB1*030202. Both alleles have been found during routine high-resolution typing by sequencing. DRB3*0218 shows a novel DRB3 gene polymorphic position, located at amino acid residue 58, alanine to glutamic acid. This residue is shared by several DRB1 alleles, including all described DRB1*11 subtypes. DQB1*030202 differs from DQB1*030201 by a point mutation at position 319 (T to C). This nucleotide change generates a new codon at amino acid position 75 that is not shared by any other DQB1 allele.     

Identification of a novel mutation in an Indian patient with CAII deficiency syndrome

Carbonic anhydrase II (CAII) deficiency syndrome characterized by osteopetrosis (OP), renal tubular acidosis (RTA), and cerebral calcifications is caused by mutations in the carbonic anhydrase 2 (CA2) gene. Severity of this disorder varies depending on the nature of the mutation and its effect on the protein. We present here, the clinical and radiographic details along with, results of mutational analysis of the CA2 gene in an individual clinically diagnosed with renal tubular acidosis, osteopetrosis and mental retardation and his family members to establish genotype-phenotype correlation. A novel homozygous deletion mutation c.251delT was seen in the patient resulting in a frameshift and a premature stop codon at amino acid position 90 generating a truncated protein leading to a complete loss of function and a consequential deficiency of the enzyme making this a pathogenic mutation. Confirmation of clinical diagnosis by molecular methods is essential as the clinical features of the CAII deficiency syndrome are similar to other forms of OP but the treatment modalities are different. Genetic confirmation of the diagnosis at an early age leads to the timely institution of therapy improving the growth potential, reduces other complications like fractures, and aids in providing prenatal testing and genetic counseling to the parents planning a pregnancy.     

Molecular basis of intermittent maple syrup urine disease: novel mutations in the E2 gene of the branched-chain α-keto acid dehydrogenase complex

The E2 gene of the branched-chain α-keto acid dehydrogenase (BCKDH) complex was studied at the molecular level in three patients with intermittent maple syrup urine disease (MSUD). All three patients had higher BCKDH activity than did those with the classical phenotype. In the first patient, a single base substitution from A to G in intron 8 created a new 5′ splice site and caused an insertion of 126 nucleotides between exons 8 and 9 by activating an upstream cryptic 3′ splice site in the same intron. The predicted mRNA encoded a truncated protein with 282 amino acids including 4 novel ones at the carboxyl terminus, compared with the normal protein with 421 amino acids. In vitro, the region from the patient but not from a normal control was recognized and was recovered as a novel exon, indicating that the single substitution was responsible for incorporation of the region into mRNA. This mutation probably supports an exon definition model in which the spliceosome recognizes a 3′ splice site and then scans downstream for an acceptable 5′ splice site, thereby defining an exon. The second patient was homozygous for a G to T transversion at nucleotide 1463 in exon 11, which predicted a substitution of the termination codon by a leucine residue and the addition of 7 extra amino acids at the carboxyl terminus. For each mutation, these two patients were homozygous and their parents were heterozygous. The third patient was a compound heterozygote for a C to G transversion at nucleotide 309 in exon 4 and a G to A transition at nucleotide 1165 in exon 9, causing an Ile-to-Met substitution at amino acid 37 and a Gly-to-Ser substitution at amino acid 323, respectively. Taken together, these results indicate that the molecular basis of intermittent phenotype MSUD in some patients can be due to mutations in the E2 gene, giving rise to a low but significant residual activity of the BCKDH complex. Received: October 29, 1997 / Accepted: November 27, 1997     

A novel mutation in the flavin-containing monooxygenase 3 gene (FMO3) of a Norwegian family causes trimethylaminuria

Loss-of-function mutations in the flavin-containing monooxygenase 3 gene (FMO3) cause the inherited disorder trimethylaminuria (TMAuria), or fish-odour syndrome. Here we describe the identification in a family from northern Norway of a novel causative mutation of TMAuria. A female child within the family presented with a TMAuria-like phenotype. The child and her mother were found to be heterozygous for a novel mutation (R238Q) in exon 6 of FMO3. The child’s father lacked this mutation, but was heterozygous for a double polymorphic variant, E158K/E308G, which was not present in the child. During a consultation with her doctor the mother mentioned an uncle whom she remembered as having a strong body odour. This discussion led to genetic counselling of the uncle and analysis of his DNA showed him to be homozygous for the R238Q mutation. Analysis of the mutant FMO3 expressed in bacteria revealed that the R238Q mutation abolished catalytic activity of the enzyme and is thus a causative mutation for TMAuria. The specificity constant (k_cat/K_M) of the K158/G308 variant was 43% of that of ancestral FMO3. Because the child is heterozygous for the R238Q mutation and no other mutation known to cause TMAuria was detected in her DNA she is predicted to suffer from transient childhood TMAuria, whereas her great-uncle has primary TMAuria.     

Normal brain myelination in a patient homozygous for a mutation that encodes a severely truncated methionine adenosyltransferase I/III

Two isozymes of mammalian methionine adenosyltransferase, MAT I and MAT III, are expressed solely in adult liver. They are, respectively, tetramers and dimers of a single subunit encoded by the gene MAT1A. A third isozyme, MAT II, contains a catalytic subunit encoded by a separate gene, MAT2A, and is expressed in a variety of tissues, including (to a slight extent) adult liver. Based on a recent finding that 2 children with isolated hypermethioninemia and brain demyelination were homozygous for MAT1A mutations predicted to produce severely truncated proteins, and devoid of activity when expressed, it was concluded that complete lack of MAT I/III activity may be associated with neurological symptoms and demyelination. We now report that a 43-year-old man with persistent isolated hypermethioninemia, previously demonstrated to have deficient MAT activity in his liver, has normal brain myelination on MRI and normal neurological function, despite being homozygous for a 539 TG insertion in exon V of MAT1A, so that the gene is predicted to encode a protein of only 184 rather than the normal 395 amino acids. This patient's exon V mutation was demonstrated by SSCP analysis and verified by sequencing. Both parents are heterozygous for the same insertion. This suggests that MAT1A mutations producing severely truncated proteins do not necessarily produce brain demyelination. This finding has relevance to a previously reported 4-year-old girl who was also homozygous for the 539insTG mutation. Finally, our patient's 7% residual hepatic MAT activity, measured at 1 mM methionine, may reflect the hepatic activity of the more ubiquitous enzyme form, MAT II. Am. J. Med. Genet. 75:395-400, 1998. © 1998 Wiley-Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.     

Simultaneous occurrence of various mutations and polymorphisms in cis and in trans of the galactose-1-phosphate uridyltransferase gene in a Turkish family with classical galactosemia

Classical galactosemia, characterized clinically by acute hepatic dysfunction, sepsis, cataract, and failure to thrive, is caused by deficiency of galactose-1-phosphate uridyltransferase (GALT). Galactose restriction normalizes these acute symptoms; however, long-term complications such as intellectual deficits and ovarian failure are conspicuous in the majority of patients. Here we report two Turkish siblings with classical galactosemia. The clinical course of the two children differed markedly: only the older girl suffered from severe acute symptoms during the neonatal period, and she developed greater mental retardation than her younger affected brother. The functional activity of GALT was virtually absent in each affected children. The mother and two healthy siblings exhibited approximately 50% normal GALT activity and the father approximately 25%. Molecular analysis revealed that these two galactosemic siblings were homozygous for a stop codon mutation of E340X in GALT exon 10. Moreover, two additional mutations, a neutral polymorphism L218L and N314D, which are typical for the Duarte-1 variant, were found in the same GALT allele. The two healthy siblings and the parents were heterozygous for these combinations of mutations. In addition, the father’s second GALT allele revealed three intron mutations at nucleotide position 1105 (G→C), 1323 (G→A) and 1391 (G→A) and the N314D mutation, which correspond to the mutations of Duarte-2 variant. Our findings indicate that in classical galactosemia several distinct mutations can be present in one allele (in cis) of the GALT gene. Therefore it seems to be necessary to examine all introns and exons of the GALT gene in galactosemic patients who do not carry the Q188R mutation or another frequent mutation in the GALT gene.

Received: 28 January 1998 / Accepted: 20 May 1998     

Homozygosity for MECP2 gene in a girl with classical Rett syndrome

We report a 21 year-old girl with classical Rett syndrome (RS) based on clinical diagnosis. The molecular testing of MECP2 gene revealed that the patient is homozygous for a de novo 473C > T mutation, causing the T158M amino acid change. Chromosome analysis showed a normal karyotype, and the haplotype analysis ruled out the possibility of parental disomy or microdeletion in MECP2 gene. Cultured fibroblast analysis reveals a mosaic for the mutation. This is a documented case of a homozygous female with RS.     

A Novel Mutation in the Complement Component 3 Gene in a Patient with Selective IgA Deficiency

Purpose

Immunological and molecular evaluation of a patient presenting with recurrent infections caused by Streptococcus pneumoniae and low complement component 3 (C3) levels.

Methods

Immunological evaluation included complement components and immunoglobulin level quantification as well as number and function of T cells, B cells and neutrophils. Serotype-specific immunoglobulin G antibodies against S. pneumoniae capsular polysaccharides were quantified by ELISA in serum samples before and after vaccination with unconjugated polysaccharide vaccine. For the molecular analysis, genomic DNA from the patient and parents were isolated and all exons as well as exon-intron boundaries of the C3 gene were sequenced by Sanger sequencing.

Results

A 16-year-old male, born to consanguineous parents, presented with recurrent episodes of pneumonia caused by S. pneumoniae and bronchiectasis. The patient showed severely reduced C3 and immunoglobulin A levels, while the parents showed moderately reduced levels of C3. Mutational analysis revealed a novel, homozygous missense mutation in the C3 gene (c. C4554G, p. Cys1518Trp), substituting a highly conserved amino acid in the C345C domain of C3 and interrupting one of its disulfide bonds. Both parents were found to be carriers of the affected allele. Vaccination against S. pneumoniae resulted in considerable clinical improvement.

Conclusions

We report a novel homozygous mutation in the C3 gene in a patient with concomitant selective IgA deficiency who presented with a marked clinical improvement after vaccination against S. pneumoniae. This observation underlines the notion that vaccination against this microorganism is an important strategy for treatment of PID patients, particularly those presenting with increased susceptibility to infections caused by this agent.     

Identification and characterization of the first mutation (Arg776Cys) in the C-terminal domain of the Human Molybdenum Cofactor Sulfurase (HMCS) associated with type II classical xanthinuria

Classical xanthinuria type II is an autosomal recessive disorder characterized by deficiency of xanthine dehydrogenase and aldehyde oxidase activities due to lack of a common sulfido-olybdenum cofactor (MoCo). Two mutations, both in the N-terminal domain of the Human Molybdenum Cofactor Sulfurase (HMCS), were reported in patients with type II xanthinuria. Whereas the N-terminal domain of HMCS was demonstrated to have cysteine desulfurase activity, the C-terminal domain hypothetically transfers the sulfur to the MoCo. We describe the first mutation in the C-terminal domain of HMCS identified in a Bedouin-Arab child presenting with urolithiasis and in an asymptomatic Jewish female. Patients were diagnosed with type II xanthinuria by homozygosity mapping and/or allopurinol loading test. The Bedouin-Arab child was homozygous for a c.2326C>T (p.Arg776Cys) mutation, while the female patient was compound heterozygous for this and a novel c.1034insA (p.Gln347fsStop379) mutation in the N-terminal domain of HMCS. Cosegregation of the homozygous mutant genotype with hypouricemia and hypouricosuria was demonstrated in the Bedouin family. Haplotype analysis indicated that p.Arg776Cys is a recurrent mutation. Arg776 together with six surrounding amino acid residues were found fully conserved and predicted to be buried in homologous eukaryotic MoCo sulfurases. Moreover, Arg776 is conserved in a diversity of eukaryotic and prokaryotic proteins that posses a domain homologous to the C-terminal domain of HMCS. Our findings suggest that Arg776 is essential for a core structure of the C-terminal domain of the HMCS and identification of a mutation at this site may contribute clarifying the mechanism of MoCo sulfuration.