Mutation screening of the fibrillin-1 (FBN1) gene in 76 unrelated patients with Marfan syndrome or Marfanoid features leads to the identification of 11 novel and three previously reported mutations

Mutations in the gene encoding fibrillin-1 (FBN1) cause Marfan syndrome (MFS) and other related connective tissue disorders. In this study we performed SSCP to analyze all 65 exons of the FBN1 gene in 76 patients presenting with classical MFS or related phenotypes. We report 7 missense mutations, 3 splice site alterations, one indel mutation, one nonsense mutation and two mutations causing frameshifts: a 16bp deletion and a single nucleotide insertion. 5 of the missense mutations (Y1101C, C1806Y, T1908I, G1919D, C2251R) occur in calcium-binding Epidermal Growth Factor-like (EGFcb) domains of exons 26, 43, 46 and 55, respectively. One missense mutation (V449I) substitutes a valine residue in the non-calcium-binding epidermal growth factor like domain (EGFncb) of exon 11. One missense mutation (G880S) affects the "hybrid" motif in exon 21 by replacing glycine to serine. The 3 splice site mutations detected are: IVS1-1G>A in intron 1, IVS38-1G>A in intron 38 and IVS46+5G>A in intron 46. C628delinsK was identified in exon 15 leading to the substitution of a conserved cysteine residue. Furthermore two frameshift mutations were found in exon 15 (1904-1919del ) and exon 63 (8025insC) leading to premature termination codons (PTCs) in exon 17 and 64 respectively. Finally we identified a nonsense mutation (R429X) located in the proline rich domain in exon 10 of the FBN1 gene. Y1101C, IVS46+5G>A and R429X have been reported before.     

Detection of eight novel palmitoyl protein thioesterase (PPT) mutations underlying infantile neuronal ceroid lipofuscinosis (INCL;CLN1)

The infantile form of neuronal ceroid lipofuscinosis (INCL; CLN1) is the earliest onset form of the neuronal ceroid lipofuscinoses (NCL), a group of progressive encephalopathies of children. INCL is caused by mutations in the palmitoyl protein thioesterase (PPT) gene, and we report here eight novel INCL mutations in PPT. Five of the mutations, c.456C>A, c.162-163insA, c.174-175delG, c.774-775insA, and a splice acceptor mutation IVS1-2A>G in intron 1, caused the generation of a premature STOP codon either directly or after a frameshift. One mutation was a three-bp insertion in exon 2 (c. 132-133insTGT) leading to insertion of one extra cysteine (Ser44-insCys-Cys45), and another mutation, a 3-bp deletion in exon 3 (c.249-251delCTT), led to deletion of Phe84 in PPT. A splice acceptor mutation IVS6-1G>T in intron 6 can be predicted to cause skipping of exon 7 in PPT. All of these novel mutations were associated with the classical phenotype of INCL, with the first symptoms starting around 12 months of age. The severe phenotypes could be explained by the nature of the novel mutations: five are predicted to lead to premature translational termination, thus abolishing the active site of PPT, and three will probably cause a misfolding of the nascent polypeptide. Thirty-five percent (7/20) of the disease alleles in these 11 families contained the most prevalent c.451C>T missense mutation outside Finland [Das et al., 1998]. Consequently, 31 different mutations underlying INCL have been found so far, the majority leading to classical INCL.     

Desmin splice variants causing cardiac and skeletal myopathy

Desmin myopathy is a hereditary or sporadic cardiac and skeletal myopathy characterised by intracytoplasmic accumulation of desmin reactive deposits in muscle cells. We have characterised novel splice site mutations in the gene desmin resulting in deletion of the entire exon 3 during the pre-mRNA splicing. Sequencing of cDNA and genomic DNA identified a heterozygous de novo A to G change at the +3 position of the splice donor site of intron 3 (IVS3+3A→G) in a patient with sporadic skeletal and cardiac myopathy. A G to A transition at the highly conserved -1 nucleotide position of intron 2 affecting the splice acceptor site (IVS2-1G→A) was found in an unrelated patient with a similar phenotype. Expression of genomic DNA fragments carrying the IVS3+3A→G and IVS2-1G→A mutations confirmed that these mutations cause exon 3 deletion. Aberrant splicing leads to an in frame deletion of 32 complete codons and is predicted to result in mutant desmin lacking 32 amino acids from the 1B segment of the alpha helical rod. Functional analysis of the mutant desmin in SW13 (vim-) cells showed aggregation of abnormal coarse clumps of desmin positive material dispersed throughout the cytoplasm. This is the first report on the pathogenic potentials of splice site mutations in the desmin gene.


Keywords: cardiac and skeletal myopathy; desmin splice site mutations; expression study; genotype-phenotype correlation     

Spectrum of splicing errors caused by CHRNE mutations affecting introns and intron/exon boundaries

Background: Mutations in CHRNE, the gene encoding the muscle nicotinic acetylcholine receptor ε subunit, cause congenital myasthenic syndromes. Only three of the eight intronic splice site mutations of CHRNE reported to date have had their splicing consequences characterised. Methods: We analysed four previously reported and five novel splicing mutations in CHRNE by introducing the entire normal and mutant genomic CHRNEs into COS cells. Results and conclusions: We found that short introns (82–109 nucleotides) favour intron retention, whereas medium to long introns (306–1210 nucleotides) flanking either or both sides of an exon favour exon skipping. Two mutations are of particular interest. Firstly, a G→T substitution at the 3'' end of exon 8 predicts an R286M missense mutation, but instead results in skipping of exon 8. In human genes, a mismatch of the last exonic nucleotide to U1 snRNP is frequently compensated by a matching nucleotide at intron position +6. CHRNE intron 8 has a mismatch at position +6, and accordingly fails to compensate for the exonic mutation at position –1. Secondly, a 16 bp duplication, giving rise to two 3'' splice sites (g.IVS10-9_c.1167dup16), results in silencing of the downstream 3'' splice site. This conforms to the scanning model of recognition of the 3'' splice site, which predicts that the first "ag" occurring after the branch point is selected for splicing.     

GH-1 gene splicing mutations: Molecular basis of hereditary isolated growth hormone deficiency in children

Children, residents of the Russian Federation, with congenital isolated growth hormone deficiency, were screened for mutations of GH-1 gene, the main gene of this deficiency. Twenty-eight children from 26 families with total congenital isolated growth hormone deficiency were examined. Direct sequencing of GH-1 detected five splicing mutations in intron 2, intron 3, and exon 4, two of them were never described previously. Three dominant negative mutations of GH-1 splicing, the basis for autosomal dominant isolated growth hormone deficiency (type II), are presented: IVS2 −2A>T, IVS3 +2T>C, and IVS3 +1G<A. GH-1 is the main gene of type II isolated growth hormone deficiency in patients living in the Russian Federation. All detected mutations of GH-1 impair splicing processes, which distinguishes them from mutations in other forms of isolated growth hormone deficiency. The detected variety of GH-1 splicing mutations attests to allele genetic heterogeneity of this pathology. The “hot spot” of mutations is 5′-donor splicing site of GH-1 intron 3, while IVS3 +1G>A mutation can be regarded as the most incident in type II isolated growth hormone deficiency in the Russian population. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 141, No. 3, pp. 324–329, March, 2006     

Splicing mutations at the HPRT locus in human T-lymphocytes in vivo

We studied 58 splicing mutations originating in vivo at the hypoxanthine guanine phosphoribosyltransferase (HPRT) locus in T-cells of 30 nonsmoking males. A nonrandom distribution of skipped exons was seen after cDNA sequence analysis, with 71% involving exons 2–3 (15), 4 (11), and 8 (15). The mutations likely to have caused the aberrant splicing were identified in 36 mutants by genomic sequencing. The most frequently observed mutations were simple base substitutions (27) and small deletions (7). Among the base substitutions, 23 occurred in the splice consensus sequences, mainly at the highly conserved dinucleotides (21), and preferentially in the acceptor sites (15). The remaining four base substitutions occurred in the coding sequence where one tandem base substitution, one single bp insertion, and two single bp deletions were also observed. The predicted change in three of the base substitutions would be a stop codon. The tandem mutation (CC → TT) occurred at position 550–551, a possible hotspot for splicing mutations (five of nine previously reported base substitutions at position 551, all C → T, resulted in abnormal splicing). Four of the base substitutions were new HPRT mutations, two in splice sites (IVS7-3T → G and IVS8 + 3A → C) and two in the coding sequence (307A → T and 594C → G). All the small deletions (>1 bp) affected the acceptor sites. The only three identified mutations related to skipping of exons 2 and 3 were located within exon 3, suggesting a frequent involvement of unknown splicing elements distant from these exons. Environ. Mol. Mutagen. 32:25–32, 1998 © 1998 Wiley-Liss, Inc.     

Molecular analyses of novel ASAH1 mutations causing Farber lipogranulomatosis: analyses of exonic splicing enhancer inactivating mutation

Farber lipogranulomatosis is a rare autosomal recessive lysosomal storage disorder caused by mutations in the ASAH1 gene. In the largest ever study, we identified and characterized ASAH1 mutations from 11 independent Farber disease (FD) families. A total of 13 different mutations were identified including 1 splice, 1 polypyrimidine tract (PPT) deletion and 11 missense mutations. Eleven mutations were exclusive to the Indian population. The IVS6+4A>G splice and IVS5‐16delTTTTC PPT deletion mutations resulted in skipping of exon 6 precluding thereby the region responsible for cleavage of enzyme precursor. A missense mutation (p.V198A) resulted in skipping of exon 8 due to inactivation of an exonic splicing enhancer (ESE) element. This is the first report of mutations affecting PPT and ESE in the ASAH1 gene resulting in FD.     

Three novel deletions in the alanine:glyoxylate aminotransferase gene of three patients with type 1 hyperoxaluria.

We describe three novel deletions in the human AGT gene in three patients with primary hyperoxaluria type 1, an autosomal recessive disease resulting from a deficiency of the liver peroxisomal enzyme, alanine glyoxylate aminotransferase (AGT; EC 2.6.1.44). A deletion of 4 nucleotides in the exon 6/intron 6 splice junction (679-IVS6+2delAAgt) is expected to cause missplicing. It would also code for a K227E missense alteration in any mRNA successfully spliced. A 2-bp deletion in exon 11 (1125-1126del CG, cDNA) results in a frameshift. A deletion of at least 5-6 kb, EX1 EX5del, spanned exons 1-5 and contiguous upstream sequence. All three deletions are heterozygous with previously documented missense mutations; the intron 6 deletion with F152I, the exon 11 deletion with G82E, and EX1 EX5del with the common mistargeting mutation, G170R.     

Compound heterozygous patient with glycogen storage disease type III: Identification of two novel AGL mutations,a donor splice site mutation of Chinese origin and a 1‐bp deletion of Japanese origin

Glycogen storage disease type III (GSD III) is an autosomal recessive disorder caused by deficiency of glycogen‐debranching enzyme (AGL). We studied a 2‐year‐old GSD III patient whose parents were from different ethnic groups. Nucleotide sequence analysis of the patient showed two novel mutations: a single cytosine deletion at nucleotide 2399 (2399delC) in exon 16, and a G‐to‐A transition at the +5 position at the donor splice site of intron 33 (IVS33+5G>A). Analysis of the mRNA produced by IVS33+5G>A showed aberrant splicing: skipping of exon 33 and activation of a cryptic splice site in exon 34. Mutational analysis of the family revealed that the 2399delC was inherited from her father, who is of Japanese origin, and the IVS33+5G>A from her mother, who is of Chinese descent, establishing that the patient was a compound heterozygote. To our knowledge, this is the first report of a mutation identified in a GSD III patient from the Chinese population. Am. J. Med. Genet. 93:211–214, 2000. © 2000 Wiley‐Liss, Inc.     

Compound heterozygous patient with glycogen storage disease type III: identification of two novel AGL mutations, a donor splice site mutation of Chinese origin and a 1-bp deletion of Japanese origin

Glycogen storage disease type III (GSD III) is an autosomal recessive disorder caused by deficiency of glycogen-debranching enzyme (AGL). We studied a 2-year-old GSD III patient whose parents were from different ethnic groups. Nucleotide sequence analysis of the patient showed two novel mutations: a single cytosine deletion at nucleotide 2399 (2399delC) in exon 16, and a G-to-A transition at the +5 position at the donor splice site of intron 33 (IVS33+5G>A). Analysis of the mRNA produced by IVS33+5G>A showed aberrant splicing: skipping of exon 33 and activation of a cryptic splice site in exon 34. Mutational analysis of the family revealed that the 2399delC was inherited from her father, who is of Japanese origin, and the IVS33+5G>A from her mother, who is of Chinese descent, establishing that the patient was a compound heterozygote. To our knowledge, this is the first report of a mutation identified in a GSD III patient from the Chinese population.