A mutation generating a stop codon in the alpha-L-fucosidase gene of a fucosidosis patient

Fucosidosis-Clinical Manifestation, Long-Term Outcomes, and Genetic Profile-Review and Case Series

Fucosidosis is a neurodegenerative disorder which progresses inexorably. Clinical features include coarse facial features, growth retardation, recurrent upper respiratory infections, dysostosis multiplex, and angiokeratoma corporis diffusum. Fucosidosis is caused by mutations in the FUCA1 gene resulting in α-L-fucosidase deficiency. Only 36 pathogenic variants in the FUCA1 gene are related to fucosidosis. Most of them are missense/nonsense substitutions; six missense and 11 nonsense mutations. Among deletions there were eight small and five gross changes. So far, only three splice site variants have been described—one small deletion, one complete deletion and one stop-loss mutation. The disease has a significant clinical variability, the cause of which is not well understood. The genotype–phenotype correlation has not been well defined. This review describes the genetic profile and clinical manifestations of fucosidosis in pediatric and adult cases.

Fucosidosis: genetic and biochemical analysis of eight cases

The molecular basis of the deficiency of alpha-L-fucosidase has been investigated in eight patients who had been diagnosed clinically and enzymatically as suffering from the autosomal recessive lysosomal storage disease fucosidosis. None of the patients had a deletion or gross alteration of the alpha-L-fucosidase gene (FUCA1). Single strand conformation polymorphism (SSCP) analysis followed by direct sequencing of amplified exons and flanking regions identified putative disease causing mutations in six of the patients, who had severe forms of the disease and very low residual alpha-L-fucosidase activity and protein. They were a 10 bp deletion in exon 1 (E113fs), a 1 bp deletion at position -2 of intron 2 (S216fs), a g-->a transition at IVS5+1, point mutations W183X and N329Y in exons 3 and 6, respectively, and a compound allele consisting of a point mutation in the signal peptide in exon 1, P5R, and a 1 bp insertion in exon 6 (Y330fs). One patient in whom an SSCP change was not detected had residual alpha-L-fucosidase activity and cross reacting protein in the heterozygous range and normal metabolism of metabolites containing fucose in his fibroblasts, consistent with the low activity polymorphism. The eighth patient, who had a partial deficiency of alpha-L-fucosidase in her fibroblasts and leucocytes at a young age but normal alpha-L-fucosidase activity and protein at a later age, was homozygous for the common Q281R polymorphism in exon 5. She had no other sequence changes and Kivlin (Peters plus) syndrome has subsequently been diagnosed. The basis of her transient deficiency of alpha-L-fucosidase is not known. The detection of five novel mutations in six severely affected patients confirms the genetic heterogeneity in fucosidosis.

Construction and characterization of secreted and chimeric transmembrane forms of Drosophila acetylcholinesterase: a large truncation of the C-terminal signal peptide does not eliminate glycoinositol phospholipid anchoring

Despite advances in understanding the cell biology of glycoinositol phospholipid (GPI)-anchored proteins in cultured cells, the in vivo functions of GPI anchors have remained elusive. We have focused on Drosophila acetylcholinesterase (AChE) as a model GPI-anchored protein that can be manipulated in vivo with sophisticated genetic techniques. In Drosophila, AChE is found only as a GPI-anchored G2 form encoded by the Ace locus on the third chromosome. To pursue our goal of replacing wild-type GPI-anchored AChE with forms that have alternative anchor structures in transgenic files, we report the construction of two secreted forms of Drosophila AChE (SEC1 and SEC2) and a chimeric form (TM-AChE) anchored by the transmembrane and cytoplasmic domains of herpes simplex virus type 1 glycoprotein C. To confirm that the biochemical properties of these AChEs were unchanged from GPI-AChE except as predicted, we made stably transfected Drosophila Schneider Line 2(S2) cells expressing each of the four forms. TM-AChE, SEC1, and SEC2 had the same catalytic activity and quaternary structure as wild type. TM-AChE was expressed as an amphiphilic membrane-bound protein resistant to an enzyme that cleaves GPI-AChE (phosphatidylinositol-specific phospholipase C), and the same percentage of TM-AChE and GPI-AChE was on the cell surface according to immunofluorescence and pharmacological data. SEC1 and SEC2 were constructed by truncating the C-terminal signal peptide initially present in GPI-AChE: in SEC1 the last 25 residues of this 34-residue peptide were deleted while in SEC2 the last 29 were deleted. Both SEC1 and SEC2 were efficiently secreted and are very stable in culture medium; with one cloned SEC1-expressing line, AChE accumulated to as high as 100 mg/liter. Surprisingly, 5-10% of SEC1 was attached to a GPI anchor, but SEC2 showed no GPI anchoring. Since no differences in catalytic activity were observed among the four AChEs, and since the same percentage of GPI-AChE and TM-AChE were on the cell surface, we contend that in vivo experiments in which GPI-AChE is replaced can be interpreted solely on the basis of the altered anchoring domain.

Isolation of the canine alpha-L-fucosidase cDNA and definition of the fucosidosis mutation in English Springer Spaniels

Fucosidosis is a lysosomal storage disorder caused by deficiency of alpha-L-fucosidase. A biochemically and clinically well characterized canine model of fucosidosis exists in a colony of English Springer Spaniels. To facilitate its use as a model for gene therapy and enzyme replacement therapy in lysosomal storage disorders displaying neurological symptoms, isolation of the canine alpha-L-fucosidase cDNA was undertaken. Both the nucleotide sequence and the predicted amino acid sequence of canine fucosidase show high levels of identity with the human and rat sequences. Fucosidosis dogs were found to have a greatly reduced level of alpha-L-fucosidase mRNA when compared with normal dogs by Northern blot analysis. Direct PCR sequencing of products generated from cDNA demonstrated a 14-bp deletion in mRNA from affected dogs. This deletion creates a frameshift mutation and introduces a premature translation termination codon at amino acid position 152 and was shown to correspond to a deletion of the last 14 base pairs of exon 1 of the canine alpha-L-fucosidase gene. Rapid PCR-based screening for the mutation has now been performed on genomic DNA from dogs within the colony, enabling detection of both carriers and homozygotes.

Two naturally occurring mouse alpha-1,2-mannosidase IB cDNA clones differ in three point mutations. Mutation of Phe592 to Ser592 is sufficient to abolish enzyme activity

In mammalian cells, alpha-1,2-mannosidases play an essential role in the early steps of N-linked oligosaccharide maturation. We previously reported (Herscovics, A., Schneikert, J., Athanassiadis, A., and Moremen, K. W. (1994) J. Biol. Chem. 269, 9864-9871) the isolation of mouse alpha-mannosidase IB cDNA clones from a Balb/c 3T3 cDNA library. Clone 4 encodes a type II membrane protein of 641 amino acids with a cytoplasmic tail of 35 amino acids, followed by a transmembrane domain and a large C-terminal catalytic domain, whereas clone 16 encodes only the last 471 amino acids. Their overlapping sequences (from amino acid 152) are identical, except for three point mutations that result in three amino acid differences in the catalytic domain of the enzyme (Thr411, Leu468, and Ser592 in clone 4 to Met411, Phe468, and Phe592 in clone 16, respectively). Both sequences could be amplified by polymerase chain reaction using templates of cDNAs derived from colon and brain of CD1 mice and from L cells derived from the C3H/An mouse, indicating that both are natural isoforms found in two inbred and one outbred mouse strains. When expressed in COS7 cells as a secreted protein A fusion protein, the catalytic domain of clone 16 displays alpha-1,2-mannosidase activity using [3H]mannose-labeled Man9GlcNAc as substrate, but the corresponding region of clone 4 is poorly secreted under identical conditions. The contribution of each point mutation to this differential secretion and enzyme activity of the two fusion proteins was assessed by testing the six recombinants corresponding to all the possible sequence permutations. Mutation of Phe592 to Ser592, as found in clone 4, is sufficient to abolish alpha-1,2-mannosidase activity, whereas mutation of Met411 to Thr411 or of Phe468 to Leu468 affects secretion with relatively little effect on enzyme activity. Phe592 is part of a highly conserved region that seems important for enzyme activity of class 1 alpha-1,2-mannosidases.

Pedigree analysis of alpha-L-fucosidase gene mutations in a fucosidosis family

Fucosidosis is an autosomal recessive lysosomal storage disease resulting from absence of alpha-L-fucosidase activity. Lymphoid cell lines from two siblings with fucosidosis and a healthy individual (control) had alpha-L-fucosidase mRNA of normal size (2.3 kb) but the level of alpha-L-fucosidase mRNA in the patients' cells was reduced. cDNA was prepared and amplified from alpha-L-fucosidase mRNA of lymphoid cells of the patients, their carrier parents, and the control. Direct DNA sequencing demonstrated three mutations in the fucosidosis family. One mutation, C1282-->T, changed the codon (CAA) for Gln-422 to a stop codon (UAA). This mutation was heterozygous (C and T) in the patients and their father and independently confirms an earlier report (J. Mol. Neurosci. (1989) 1, 177). Another mutation, C247-->T, changed the codon (CAG) for Gln-77 to a stop codon (UAG) and was heterozygous (C and T) in the patients and their mother. The third mutation, A860-->G, changed the codon CAG for Gln-281 to the codon (CGG) for Arg and was heterozygous (A and G) in the patients but homozygous in their father. alpha-L-Fucosidase activity in cells of the father was 37% of controls indicating that homozygosity of the A860-->G mutation did not cause an absence of alpha-L-fucosidase activity and fucosidosis. This mutation probably results in a normal polymorphic variant of alpha-L-fucosidase. It is proposed that the combination of the C247-->T mutation on the maternal allele of the alpha-L-fucosidase gene and the C1282-->T mutation on the paternal allele caused fucosidosis in the patients.