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A novel frameshift mutation (141delT) in exon 1 of the 21-hydroxylase gene (CYP21) in a patient with the salt wasting form of congenital adrenal hyperplasia. Mutation in brief no. 255. Online.

Congenital adrenal hyperplasia (CAH) is a common autosomal recessive disease with a wide range of clinical manifestation. In 90-95% of the cases it is caused by 21-hydroxylase deficiency (OMIM #201910) due to mutations of the CYP21 gene (GDB Accession #M12792). In most cases the CYP21-inactivating point mutations are transferred by apparent gene conversions from CYP21P to CYP21. In only a few cases point mutations have been described, which are not present in the pseudogene. Using Southern blot analysis and DNA sequencing we have identified a novel mutation (141delT) of the CYP21 gene in a patient suffering from the salt wasting form of CAH. This results in a premature termination of a truncated protein at amino acid position 51 (L51X), which is likely to result in an enzyme with no activity. This novel mutation has not been reported to occur in the CYP21P alleles and it was not found in the CYP21P alleles in this CAH family.

Adrenal Hyperplasia, Congenital↗

Two novel missense and frameshift mutations in exons 5 and 6 of the purine nucleoside phosphorylase (PNP) gene in a severe combined immunodeficiency (SCID) patient.

Four percent of human severe combined immunodeficiency cases are caused by a deficiency of the enzyme purine nucleoside phosphorylase (PNP). In this study we investigated the molecular basis for this rare autosomal recessive disease. Sequence analyses led to the identification of two new mutations in the PNP gene: an A to G transition in exon 5, which leads to the substitution of tyrosine 192 by a cysteine residue, and a 1-bp deletion in exon 6, which causes premature translation termination of the PNP protein. Both PNP mutations affect predicted major structural motifs of the protein and result in post-translation instability of the enzyme.

Alleles↗

Striate palmoplantar keratoderma resulting from a frameshift mutation in the desmoglein 1 gene.

BACKGROUND: Striate keratodermas (PPKS) are a group of rare autosomal dominant palmoplantar keratodermas, characterized by a thickening of the skin on the palms and soles. PPKS is characterized by hyperkeratosis extending along the length of each finger and on the palm of the hand, as well as by patches of hyperkeratosis on the soles. OBJECTIVE: We report a four-generation Pakistani kindred in which 11 members were affected with PPKS. METHODS: Based on previous reports of DSG1 mutations in PPKS, we performed direct DNA sequencing analysis. RESULTS: Clinically, these patients presented with hyperkeratotic palms and with linear hyperkeratosis on the fingers. Additionally, focal hyperkeratosis was seen on the sole of the toes as well as the ball and heel of the foot. DNA sequencing analysis revealed a heterozygous G-to-T transversion in the 3' splice acceptor site of intron 11 of the DSG1 gene designated 1688 -1 G>T. We predict that this mutation will lead to the skipping of exon 12 which is out of frame (134nt), subsequent degradation of the mutant mRNA by non-sense mediated RNA decay, and haploinsufficiency for DSG1. CONCLUSION: We report a novel splice site mutation in the DSG1 gene in PPKS, which further underscores the significance of the desmoglein gene family in diseases of epidermal integrity.

Desmoglein 1↗

Ocular findings in a family with autosomal dominant retinitis pigmentosa and a frameshift mutation altering the carboxyl terminal sequence of rhodopsin.

A family is described in which an 8 base pair deletion (nucleotides 5252-5259, codons 341-343) of the rhodopsin gene cosegregates with autosomal dominant retinitis pigmentosa (adRP). The deletion results in a shift in the reading frame, causing a rhodopsin molecule extended by one residue and substantially altered at the carboxyl terminus. Phenotypic expression is relatively mild. In affected members, night blindness did not occur before the age of 16, and late onset of visual field loss was consistently reported. Even older individuals (59 and 76 years) had preserved central islands in the visual field; a younger female patient had normal visual fields until the age of 34. ERG and psychophysical tests showed well preserved cone function at stages of virtually abolished rod function. Phenotypic differences and similarities between this form of adRP and others associated with mutations at the carboxyl terminus of the rhodopsin molecule are discussed. The cause of RP by mutations in this region remains to be clarified.

Adult↗

Compound heterozygosity of a frameshift mutation in the coding region and a single base substitution in the promoter of the ACTH receptor gene in a family with isolated glucocorticoid deficiency.

Isolated glucocorticoid deficiency (IGD) is an autosomal recessive syndrome characterized by glucocorticoid insufficiency without mineralocorticoid deficiency. Mutations in the coding region of the ACTH receptor (MC2R) have been reported in several families with IGD. We amplified and sequenced the entire MC2R coding region in a new family with IGD. The proband was found to be heterozygous (paternal allele) for the mutation Gly217fs, which changes the open reading frame of the MC2R protein resulting in a truncated receptor. No other abnormality was found in the MC2R coding region. However, sequencing of the promoter region of the MC2R gene (-1017/44 bp) of the proband revealed a heterozygous T-->C substitution in the maternal allele at -2 bp position from initiation of the transcription start site. This substitution was found in only 6.5% in a healthy unrelated population. Constructs containing this polymorphism consistently showed a significant 15% decrease in promoter activity compared to wild type. In conclusion, we provide evidence that the IGD in this previously unreported family with ACTH resistance appears to be secondary to compound heterozygosity of a coding region and a promoter mutation in the MC2R gene.

Adolescent↗

A frameshift mutation in Exon V of the A alpha-chain gene leading to truncated A alpha-chains in the homozygous dysfibrinogen Milano III.

An inherited dysfunctional fibrinogen variant, denoted as fibrinogen Milano III, was found in a 13-year-old girl suffering from recurrent venous thrombosis. Plasma of the patient exhibited prolonged thrombin time and Reptilase time. Polymerization of fibrin monomers in the presence and absence of calcium ions was strongly impaired. SDS-polyacrylamide gel electrophoresis of reduced fibrinogen showed normal B beta- and gamma-chains, whereas no normal A alpha-chain was detected in the proposita. Immunoblot analysis with the monoclonal antibody Y18, detecting an epitope within the stretch of amino acids A alpha 1-51, revealed an A alpha-chain of about 50 kDa with an intact amino terminus. Immunoblotting with antibodies directed against serum albumin demonstrated the presence of albumin covalently linked to fibrinogen via a disulfide bridge. The structural defect of fibrinogen Milano III was determined by sequence analysis of a single-stranded fragment of genomic DNA amplified by polymerase chain reaction. An insertion of a thymine in the exon V of the A alpha-chain gene after the triplet ATT coding for IleA alpha 451 altered the reading frame and caused premature termination of the protein synthesis (Trp452(TGG)-Ser453(TCC)-Stop454(TGA)). In both parents, normal and mutant alleles were established, leading to duplication of the sequence pattern after the thymine insertion site, whereas the proposita is homozygous for the new mutation in the fibrinogen A alpha-chain gene.

Base Sequence↗

Phosphorylase kinase deficiency in I-strain mice is associated with a frameshift mutation in the alpha subunit muscle isoform.

Heritable phosphorylase kinase (Phk) deficiency underlies a group of glycogenoses in humans, mice and rats that differ in mode of inheritance and tissue-specificity. It is assumed that this heterogeneity is caused by mutations affecting different subunits and isoforms of Phk. As the first Phk deficiency mutation to be identified, we report a single-nucleotide insertion in the coding sequence of the Phk alpha subunit muscle isoform of the I-strain mouse. This mutation accounts for the virtually complete enzymatic deficiency, the tissue specificity and the X-linked mode of inheritance in this mutant.

Amino Acid Sequence↗

A novel frameshift mutation in the McLeod syndrome gene in a Japanese family.

We report a novel mutation in the XK gene (XK) in a Japanese patient with McLeod syndrome. A 50-year-old man showed progressive muscular atrophy, choreic movement, elevated level of serum creatinine kinase, and acanthocytosis. The expression level of all the Kell antigens in erythrocyte was decreased and molecular analysis revealed a single-base (T) deletion at the nucleotide position 1095 in XK. This deletion caused a frameshift in translation, leading to a premature stop codon at the amino acid position 408. We conclude this single-base deletion causes defective Kx protein, which is responsible for the McLeod phenotype in this patient.

Amino Acid Transport Systems, Neutral↗

Neutrophil-specific granule deficiency: homozygous recessive inheritance of a frameshift mutation in the gene encoding transcription factor CCAAT/enhancer binding protein--epsilon.

Neutrophil-specific granule deficiency (SGD) is a rare congenital disorder. The neutrophils of individuals with SGD display atypical bi-lobed nuclei, lack expression of all secondary and tertiary granule proteins, and possess defects in chemotaxis, disaggregation, receptor up-regulation, and bactericidal activity, resulting in frequent and severe bacterial infections. Previously, a homozygous mutation in the CCAAT/enhancer binding protein-epsilon (C/EBPepsilon) gene was reported for one case of SGD. To substantiate the role of C/EBPepsilon in the development of SGD and elucidate its mechanism of inheritance, the mutational status of the gene was determined in a second individual. An A-nucleotide insertion in the coding region of the C/EBPepsilon gene was detected. This mutation completely abolished the predicted translation of all C/EBPepsilon isoforms. Microsatellite and nucleotide sequence analyses of the C/EBPepsilon locus in the parents of the proband indicated that the disorder may have resulted from homozygous recessive inheritance of the mutant allele from an ancestor shared by both parents. The mutant C/EBPepsilon(32) protein localized in the cytoplasm rather than the nucleus and was unable to activate transcription. Consistent with this, a significant decrease in the levels of the messenger RNAs (mRNAs) encoding the secondary granule protein human 18-kd cationic antimicrobial protein (hCAP-18)/LL-37 and the primary granule protein bactericidal/permeability-increasing protein were observed in the patient. The hCAP-18 mRNA was induced by overexpression of C/EBPepsilon(32) in the human myeloid leukemia cell line, U937, supporting the hypothesis that C/EBPepsilon is a key regulator of granule gene synthesis. This study strongly implicates mutation of the C/EBPepsilon gene as the primary genetic defect involved in the development of neutrophil SGD and defines its mechanism of inheritance.

Adult↗

Frameshift mutation in exon 3 of the lipoprotein lipase gene causes a premature stop codon and lipoprotein lipase deficiency.

Several mutations in the human lipoprotein lipase (LPL) gene have been shown to underlie LPL deficiency. These mutations occur in patients who are mainly of European descent, and comprise a single base transition causing a premature stop codon, four separate amino acid substitutions and two large gene rearrangements. Together they account for approximately 40% of the LPL alleles in a cohort of 50 patients whose DNA has been examined in this laboratory. We now report on a new mutation in exon 3 of the LPL gene from a South African subject of South-east Asian extraction. This mutation comprises a six base-pair insertion at the site of a single base deletion. The net insertion of five base-pairs at amino acid positions 102 to 103 causes a shift in the reading frame, generating 44 amino acid residues of random sequence and a premature stop codon within exon 4. This mutation is predicted to result in the synthesis of a markedly truncated protein and is the cause of the enzyme deficiency in our patient.

Adult↗

Three severe cases of EBS Dowling-Meara caused by missense and frameshift mutations in the keratin 14 gene.

We report three unrelated patients affected at birth with an unusually severe form of epidermolysis bullosa simplex Dowling-Meara type (EBS-DM) because of mutations in KRT14 encoding keratin 14. Two patients were heterozygous for the previously described p.M119T mutation. The third patient was heterozygous for a novel c.1246delC mutation predicting the replacement of the helix termination peptide and the tail domain by a 25 amino-acid aberrant carboxyterminal sequence. At age 2 years, patients carrying the p.M119T mutation still suffered from severe EBS-DM, whereas the patient harboring the c.1246delC mutation has improved over time. These cases illustrate genotype-phenotype correlations and have implications for genetic counselling of EBS.

Child, Preschool↗

Transcript analysis of CFTR frameshift mutations in lymphocytes using the reverse transcription-polymerase chain reaction technique and the protein truncation test.

mRNA transcripts of the cystic fibrosis transmembrane conductance regulator (CFTR) gene were analyzed from lymphocytes of two cystic fibrosis compound heterozygotes (394delTT/3195del6 and 1215delG/ 2423delG), of five related carriers heterozygous for one of these mutations, and of five normal individuals. After reverse transcription of total RNA and amplification by the polymerase chain reaction, fragments were investigated by sequencing and by the protein truncation test (PTT). The three frameshift mutants were correctly detected by PTT, as they introduced a premature termination codon resulting in shortened protein products. The PTT approach thus provides a simple and reliable alternative method for detecting frameshift, nonsense, or splice site mutations, and for ascertaining their putative effect on the reading frame of the mRNA. In addition, we have identified 6 alternatively spliced forms of CFTR mRNA, two of which (transcripts lacking 4 + 5 or 17B) have not been described previously.

Adolescent↗