[Proteomics, a new tool for an accurate typing of amyloidosis]

Amyloidosis is a rare group of diseases related to extracellular deposition of proteins in an insoluble beta-pleated sheet structure presenting a characteristic apple-green birefringence under polarized light after Congo red staining. Thirty types of proteins are known to cause amyloidosis. The accurate identification of the amyloid protein is of paramount importance since it is a key step for the clinical management and personalized treatment. Amyloid typing is usually based on immunohistochemistry and immunofluorescence on tissular sections. This approach has several limits leading to a subtyping failure rate of 15 to 58% of cases. To overcome these difficulties, proteomic methods have been developed to characterize directly the amyloid protein. The most advanced technique carried out on fixed and paraffin-embedded tissue consists of laser microdissection followed by mass spectrometry. The type of amyloidosis can be determined in more than 95% of cases. However, the experience for this technique is very limited apart from the Mayo Clinic (Rochester, United States). In France, a very close proteomic assay has been implemented in the department of pathology of Foch Hospital with similar results. The introduction of proteomics in clinical practice represents a major improvement for typing amyloidosis. In this article, we discuss the benefits and limits of the different techniques used for amyloid classification and we briefly report our proteomic results.

A new family with hereditary lysozyme amyloidosis with gastritis and inflammatory bowel disease as prevailing symptoms

Background

Systemic amyloidoses is a heterogeneous group of diseases either acquired or hereditary. Amyloidoses can involve the gastrointestinal tract and the nature of the precursor protein that forms the fibrils deposits should be identified to adjust the treatment and evaluate the prognosis. Lysozyme amyloidosis (ALys) is a rare, systemic non neuropathic hereditary amyloidosis with a heterogenous phenotype including gastrointestinal, renal and hepatic symptoms.

Case presentation

We report and describe symptoms and gastrointestinal tract involvement in a new family with hereditary lysozyme amyloidosis. Clinical manifestations and organ involvement of nine affected members of a new family with the p.Trp82Arg ALys variant were recorded. All affected individuals suffered with prevailing gastrointestinal symptoms leading to the diagnosis of ALys. 8/9 had non specific upper gastrointestinal symptoms and 3/9 had rectocolic inflammation evoking inflammatory bowel disease. No other organ involvement by amyloidosis was found. Histological examination revealed amyloid deposits in all cases and all carried the p.Trp82Arg ALys variant at a heterozygous state.

Conclusion

Hereditary amyloidosis associated with the p.Trp82Arg lysozyme variant in this new family is predominantly associated with mild upper gastrointestinal tract involvement and in some cases with inflammatory bowel disease. Amyloidosis should be considered in atypical or treatment resistant, upper or lower chronic gastrointestinal symptoms. When associated with a familial history a lysozyme gene mutation must be searched.

A family with Wagner syndrome with uveitis and a new versican mutation

PURPOSE

To report the clinical and molecular findings of a kindred with Wagner syndrome (WS) revealed by intraocular inflammatory features.

METHODS

Eight available family members underwent complete ophthalmologic examination, including laser flare cell meter measurements. Collagen, type II, alpha 1, versican (VCAN), frizzled family receptor 4, low density lipoprotein receptor-related protein 5, tetraspanin 12, and Norrie disease (pseudoglioma) genes were screened with direct sequencing.

RESULTS

The index case was initially referred for unexplained severe and chronic postoperative bilateral uveitis following a standard cataract surgery procedure. Clinical examination of the proband revealed an optically empty vitreous with avascular vitreous strands and veils, features highly suggestive of WS. The systematic familial ophthalmologic examination identified three additional unsuspected affected family members who also presented with the WS phenotype, including uveitis for one of them. We identified a novel c.4004-6T>A nucleotide substitution at the acceptor splice site of intron 7 of the VCAN gene that segregated with the disease phenotype.

CONCLUSIONS

We present a family with WS with typical WS features and intraocular inflammatory manifestations associated with a novel splice site VCAN mutation. Beyond the structural role in the retinal-vitreous architecture, versican is also emerging as a pivotal mediator of the inflammatory response, supporting uveitis predisposition as a clinical manifestation of WS.

Custom oligonucleotide array-based CGH: a reliable diagnostic tool for detection of exonic copy-number changes in multiple targeted genes

The frequency of disease-related large rearrangements (referred to as copy-number mutations, CNMs) varies among genes, and search for these mutations has an important place in diagnostic strategies. In recent years, CGH method using custom-designed high-density oligonucleotide-based arrays allowed the development of a powerful tool for detection of alterations at the level of exons and made it possible to provide flexibility through the possibility of modeling chips. The aim of our study was to test custom-designed oligonucleotide CGH array in a diagnostic laboratory setting that analyses several genes involved in various genetic diseases, and to compare it with conventional strategies. To this end, we designed a 12-plex CGH array (135k; 135 000 probes/subarray) (Roche Nimblegen) with exonic and intronic oligonucleotide probes covering 26 genes routinely analyzed in the laboratory. We tested control samples with known CNMs and patients for whom genetic causes underlying their disorders were unknown. The contribution of this technique is undeniable. Indeed, it appeared reproducible, reliable and sensitive enough to detect heterozygous single-exon deletions or duplications, complex rearrangements and somatic mosaicism. In addition, it improves reliability of CNM detection and allows determination of boundaries precisely enough to direct targeted sequencing of breakpoints. All of these points, associated with the possibility of a simultaneous analysis of several genes and scalability 'homemade' make it a valuable tool as a new diagnostic approach of CNMs.

[Amyloid polyneuropathies--biochemical and genetic aspects]

Familial amyloid polyneuropathies (FAP) are among the most frequent hereditary amyloidoses. These are serious, most often fatal diseases with autosomal dominant inheritance. FAP can be caused by mutations in four genes, namely those encoding transthyretin, Al-apoliprotein, gelsolin, and beta-2 microglobulin. Transthyretin is a tetramer composed of four identical subunits linked by non covalent bonds and bearing binding sites for thyroxine (T4) and retinol-binding protein (RBP). More than 120 transthyretin gene sequence variations have been characterized, of which only 80% seem to be pathogenic. Gene mutations can induce tetramer destabilization, thereby generating misfolded monomers that aggregate into insoluble amyloidfibrils. The mutation spectrum is highly variable across countries. For example, while the Val30Met mutation is found in 95% of the Portuguese and Swedish patient populations, high mutational heterogeneity is observed in France. Age of onset and clinical signs are influenced by numerous factors, especially the mutation type and the country, but the mechanisms underlying this variability are not fully clear. The three-dimensional structure of the normal transthyretin protein and a dozen mutants is now known, providing insights into the deleterious effects of mutations. A better understanding of the mechanisms involved in amyloid fibril formation has led to the development of drugs that inhibit transthyretin tetramer destabilization. It is hoped that, within afew years, such drugs will replace liver transplantation, which is currently the only curative treatment.

Hereditary systemic amyloidosis due to Asp76Asn variant β2-microglobulin

We describe a kindred with slowly progressive gastrointestinal symptoms and autonomic neuropathy caused by autosomal dominant, hereditary systemic amyloidosis. The amyloid consists of Asp76Asn variant β(2)-microglobulin. Unlike patients with dialysis-related amyloidosis caused by sustained high plasma concentrations of wild-type β(2)-microglobulin, the affected members of this kindred had normal renal function and normal circulating β(2)-microglobulin values. The Asp76Asn β(2)-microglobulin variant was thermodynamically unstable and remarkably fibrillogenic in vitro under physiological conditions. Previous studies of β(2)-microglobulin aggregation have not shown such amyloidogenicity for single-residue substitutions. Comprehensive biophysical characterization of the β(2)-microglobulin variant, including its 1.40-Å, three-dimensional structure, should allow further elucidation of fibrillogenesis and protein misfolding.

A new VCAN/versican splice acceptor site mutation in a French Wagner family associated with vascular and inflammatory ocular features

PURPOSE

To detail the highly variable ocular phenotypes of a French family affected with an autosomal dominantly inherited vitreoretinopathy and to identify the disease gene.

METHODS

Sixteen family members with ten affected individuals underwent detailed ophthalmic evaluation. Genetic linkage analysis and gene screening were undertaken for genes known to be involved in degenerative and exudative vitreoretinopathies. Qualitative reverse transcriptase-PCR analysis of the versiscan (VCAN) transcripts was performed after mutation detection in the VCAN gene.

RESULTS

The first index patient of this French family was referred to us because of a chronic uveitis since infancy; this uveitis was associated with exudative retinal detachment in the context of a severe uncharacterized familial vitreoretinopathy. Genetic linkage was obtained to the VCAN locus, and we further identified a new pathogenic mutation at the highly conserved splice acceptor site in intron 7 of the VCAN gene (c.4004-2A>T), which produced aberrantly spliced VCAN transcripts.

CONCLUSIONS

Extensive molecular investigation allowed us to classify this familial vitreoretinopathy as Wagner syndrome. This study illustrates the need to confirm clinical diagnosis by molecular genetic testing and adds new ocular phenotypes to the Wagner syndrome, such as vascular and inflammatory features.

Genotype-phenotype correlations of TGFBI p.Leu509Pro, p.Leu509Arg, p.Val613Gly, and the allelic association of p.Met502Val-p.Arg555Gln mutations

PURPOSE

Investigate the genotype-phenotype correlations for five TGFBI (transforming growth factor, beta-induced) mutations including one novel pathogenic variant and one complex allele affecting the fourth FAS1 domain of keratoepithelin, and their potential effects on the protein's structure.

METHODS

Three unrelated families were clinically diagnosed with lattice corneal dystrophy (CD) and one with an unclassified CD of Bowman's layer. Mutations in the TGFBI gene were detected by direct sequencing, and the functional impact of each variant was predicted using in silico algorithms. Corneal phenotypes, including histological examinations, were compared with the literature data. Furthermore, molecular modeling studies of these mutations were performed.

RESULTS

Two distinct missense mutations affecting the same residue at position 509 of keratoepithelin: p.Leu509Pro (c.1526T>C) and p.Leu509Arg (c.1526T>G) were found to be associated with a lattice-type CD. The novel p.Val613Gly (c.1828T>G) TGFBI mutation was found in a sporadic case of an Algerian individual affected by lattice CD. Finally, the Bowman's layer CD was linked to the association in cis of the p.Met502Val and p.Arg555Gln variants, leading to the reclassification of this CD as atypical Thiel-Behnke CD. Structural modeling of these TGFBI mutations argues in favor of these mutations being responsible for instability and/or incorrect folding of keratoepithelin, predictions that are compatible with the clinical diagnoses.

CONCLUSIONS

Description of a novel TGFBI mutation and a complex TGFBI allele further extends the mutational spectrum of TGFBI. Moreover, we show convincing evidence that TGFBI mutations affecting Leu509 are linked to the lattice phenotype in two unrelated French families, contrasting with findings previously reported. The p.Leu509Pro was reported to be associated with both amyloid and non-amyloid aggregates, whereas p.Leu509Arg has been described as being responsible for Epithelial Basement Membrane Dystrophy (EBMD).

Homozygous nonsense mutation in the FOXE3 gene as a cause of congenital primary aphakia in humans

Congenital primary aphakia (CPA) is a rare developmental disorder characterized by the absence of lens, the development of which is normally induced during the 4th-5th wk of human embryogenesis. This original failure leads, in turn, to complete aplasia of the anterior segment of the eye, which is the diagnostic histological criterion for CPA. So far, the genetic basis for this human condition has remained unclear. Here, we present the analysis of a consanguineous family with three siblings who had bilateral aphakia, microphthalmia, and complete agenesis of the ocular anterior segment. We show that a null mutation in the FOXE3 gene segregates and, in the homozygous state, produces the mutant phenotype in this family. Therefore, this study identifies--to our knowledge, for the first time--a causative gene for CPA in humans. Furthermore, it indicates a possible critical role for FOXE3 very early in the lens developmental program, perhaps earlier than any role recognized elsewhere for this gene.

H244R VSX1 is associated with selective cone ON bipolar cell dysfunction and macular degeneration in a PPCD family

PURPOSE

To elucidate the retinal dysfunction and the molecular basis of posterior polymorphous corneal dystrophy (PPCD) associated with macular dystrophy, both inherited in a dominant manner through a three-generation family.

METHODS

Ophthalmologic examinations including slit lamp examination, visual acuity tests, fundus visualization by scanning laser ophthalmoscopy, fluorescein angiography, color vision tests, electro-oculography, photopic and scotopic electroretinography (ERG) according to the International Society for Clinical Electrophysiology of Vision (ISCEV) protocols, and oscillatory potential (OP) recordings were conducted on affected family members. Corneal button from one affected patient was examined by transmission electron microscopy. All exons and intron-exon boundaries of the VSX1 and the COL8A2 genes were amplified by polymerase chain reaction and sequenced.

RESULTS

The presence of endothelial cells that have epithelial-like features with multiple layers, desmosomal junctions, and microvillous projections supports the diagnosis of PPCD. Sequence analysis indicated that the H244R variant in the VSX1 segregated with corneal and macular disease phenotypes in this family. Electrophysiologic studies indicated normal scotopic ERG findings, decreased amplitude of the photopic b-wave, photopic OP2 and OP3 barely recordable with a preserved OP4 amplitude, and variably decreased 30-Hz flicker amplitude.

CONCLUSIONS

The human VSX1 is required for cone ON bipolar cell function but not for rod and cone OFF bipolar cells, giving a unique example of such a selective heritable retinal defect in humans. Furthermore, the authors provide the first clinical support for a new alternative role of VSX1 in cone biology, probably similar to that proposed for its goldfish ortholog during retinal differentiation.

Lysozyme amyloidosis: report of 4 cases and a review of the literature

Autosomal dominant hereditary amyloidosis represents not 1 disease but a group of diseases, each the result of mutations in a specific protein. The most common form is transthyretin amyloidosis, which has been recognized clinically for over 50 years as a familial polyneuropathy. Nonneuropathic amyloidoses (Ostertag type amyloidosis) include those due to abnormalities in lysozyme, fibrinogen Aalpha-chain, and apolipoprotein A-I and A-II. The role of lysozyme in amyloid-related human disorders was first described in 1993; to date, there have been only 9 publications describing this disorder, which is a nonneuropathic form of hereditary amyloidosis. Reported cases have involved 7 unrelated families. We describe here our own experience with 4 families suffering from lysozyme amyloidosis: the first had prominent renal manifestations with sicca syndrome, the second and third had prominent gastrointestinal symptoms, and the fourth had a dramatic bleeding event due to rupture of abdominal lymph nodes. To our knowledge, this last symptom has not been reported previously, but is reminiscent of the hepatic hemorrhage seen in a previously reported case of a patient with lysozyme amyloidosis. To characterize the manifestations of this disorder, we performed an exhaustive literature review.Although hereditary amyloidosis is thought to be a rare disease, it is probably not as rare as we think and may well be underdiagnosed. Moreover, some cases of lysozyme amyloidosis are probably confused with acquired monoclonal immunoglobulin light-chain (AL) amyloidosis, formerly known as primary amyloidosis, which is the most frequent type of amyloidosis. Because treatment for each type of amyloidosis is different, and because therapy directed at 1 type may worsen symptoms of the other types, it is important to determine precisely the nature of the amyloid protein. Thus, hereditary lysozyme amyloidosis should be considered in all patients with systemic amyloidosis, particularly in patients who present with renal, gastrointestinal, or bleeding complications without evidence of AL or AA (secondary) amyloidoses.

Truncating mutations in the carbohydrate sulfotransferase 6 gene (CHST6) result in macular corneal dystrophy

PURPOSE

Identification of mutations in the CHST6 gene in 15 patients from 11 unrelated families affected with recessive macular corneal dystrophy (MCD).

METHODS

Genomic DNA was extracted from peripheral blood leukocytes of the affected patients and their healthy family members, and the mutational status of the CHST6 gene was determined for each patient by a PCR-sequencing approach. Serum concentrations of antigenic keratan sulfate for each proband were determined by ELISA.

RESULTS

ELISA indicated that all affected patients, except one, were of MCD type I or IA. Fourteen distinct mutations were identified within the CHST6 coding region: 2 nonsense, 2 frameshift, and 10 missense. Of these, 12 were novel, and a nonsense mutation in the homozygous state is reported for the first time.

CONCLUSIONS

These molecular results in French patients with MCD combined with those reported in previous studies indicated CHST6 mutational heterogeneity. The characterization herein of nonsense mutations is in keeping with the fact that MCD results from loss of function of the CHST6 protein product.

Transthyretin mutation (TTRGly47Ala) associated with familial amyloid polyneuropathy in a French family

A French family in which three individuals had familial amyloid polyneuropathy (FAP) was investigated. The proband presented cardiomyopathy with atrial arrhythmia and then developed axonal polyneuropathy, carpal tunnel syndrome, and sclerodactyly. Nucleotide sequencing of exons 2, 3 and 4 of the transthyretin (TTR) gene revealed heterozygosity for a single base change in the second position of codon 47. This G to C transversion predicts replacement of a glycine by an alanine at position 47 in the mature protein. This mutation (G47A) was previously identified in two different families of Italian origin both of which had FAP and cardiomyopathy. Here we report the first identification of this mutation in a non-Italian family.

Skewed X-chromosome inactivation in monochorionic diamniotic twin sisters results in severe and mild hemophilia A

This study describes the genetic mechanisms responsible for the de novo occurrence of severe and mild hemophilia A in monozygotic twin females. Both twins were found to carry a previously known factor VIII mutation (Tyr16Cys) in the heterozygous state which most probably arose in the paternal germ line. Both twins showed concordant skewing of X inactivation toward the maternally derived normal X chromosome, the most severely affected twin exhibiting a higher percentage of inactivation of the normal X chromosome. The degree of skewing of X inactivation closely correlated with both the coagulation parameters and the clinical phenotype of the twins. Since these twins were monochorionic, such results suggest that the twinning event in this case has occurred after the onset of the X-inactivation period.