[National protocol for diagnosis and care of congenital aniridia: Summary for the attending physician]

Congenital aniridia is a rare panocular disease defined by a national diagnostic and care protocol (PNDS) validated by the HAS. In most cases, it is due to an abnormality in the PAX6 gene, located at 11p13. Aniridia is a potentially blinding autosomal dominant disease with high penetrance. The prevalence varies from 1/40,000 births to 1/96,000 births. Approximately one third of cases are sporadic. Ocular involvement includes complete or partial absence of iris tissue, corneal opacification with neovascularization, glaucoma, cataract, foveal hypoplasia, optic disc hypoplasia and ptosis. These ocular disorders coexist to varying degrees and progress with age. Congenital aniridia manifests in the first months of life as nystagmus, visual impairment and photophobia. A syndromic form such as WAGR syndrome, WAGRO syndrome (due to the risk of renal Wilms tumor) or Gillespie syndrome (cerebellar ataxia) must be ruled out. Systemic associations may include diabetes, due to expression of the PAX6 gene in the pancreas, as well as other extraocular manifestations. Initial assessment is best carried out in a referral center specialized in rare ophthalmologic diseases, with annual follow-up. The management of progressive ocular involvement must be both proactive and responsive, with medical and surgical management. Visual impairment and photophobia result in disability, leading to difficulties in mobility, movement, communication, learning, fine motor skills, and autonomy, with consequences in personal, school, professional, socio-cultural and athletic life. Medico-socio-educational care involves a multidisciplinary team. Disability rehabilitation must be implemented to prevent and limit situations of handicap in activities of daily living, relying on the Commission for the Rights and Autonomy of People with Disabilities (CDAPH) within the Departmental House of People with Disabilities (MDPH). The general practitioner coordinates multidisciplinary medical and paramedical care.

[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.

Recurrent subarachnoid hemorrhage associated with a new transthyretin variant (Gly53Glu)

CNS involvement is rare in systemic amyloidoses due to transthyretin (TTR) mutation and manifests as a combination of dementia, seizures, and myelopathy. The authors report two French siblings who experienced recurrent subarachnoid hemorrhages as the main clinical feature. Brain specimens showed that the leptomeningeal vessels walls were thickened by amyloid deposits, and sequencing of the TTR exons showed a heterozygous single base-pair transition from G to A (codon 53), resulting in a glycine for glutamic acid substitution (G53E).

Histologic phenotype-genotype correlation of corneal dystrophies associated with eight distinct mutations in the TGFBI gene

PURPOSE

To establish a phenotype-genotype correlation of various autosomal-dominant corneal dystrophies among French subjects.

DESIGN

Retrospective molecular genetic study and clinicopathologic correlation.

PARTICIPANTS

Forty-four subjects from 26 unrelated French families were included in this study, and 60 corneal buttons could be examined at the histologic and ultrastructural levels.

METHODS

Light microscopy and transmission electron microscopy were performed on corneal specimens obtained during keratoplasty. Blood samples were collected for DNA analysis.

MAIN OUTCOME MEASURES

After genomic DNA extraction from peripheral blood leukocytes of each family member, exons of the TGFBI gene were amplified by polymerase chain reaction (PCR), and the PCR products were directly sequenced on both strands.

RESULTS

Four different mutations were found to be responsible for dystrophy of granular type (R555W, R124L, R124H, and R124L+delT125-delE126), three other different mutations produced a lattice type (R124C, H626R, and A546T), and the last mutation identified was associated with the honeycomb-shaped dystrophy (R555Q). Each subtype of dystrophy showed, histologically and ultrastructurally, specific characteristics that are easily recognizable. However, besides these stereotyped forms, differential histologic diagnosis of atypical forms remains difficult, and these forms could be misdiagnosed.

CONCLUSIONS

The characteristic biomicroscopic appearance and histopathologic features of each "classic" dystrophy present a significant degree of specificity and generally provide an accurate diagnosis. However, atypical forms in which clinical and histologic data alone could be misleading, are unequivocally diagnosed after DNA analysis.

Unbalanced X-chromosome inactivation with a novel FVIII gene mutation resulting in severe hemophilia A in a female

This report is of a 14-month-old girl affected with severe hemophilia A. Both her parents had normal values for factor VIII activity, and von Willebrand disease type 2N was excluded. Karyotype analysis demonstrated no obvious alteration, and BclI Southern blot did not reveal F8 gene inversions. Direct sequencing of F8 gene exons revealed a frameshift-stop mutation (Q565delC/ter566) in the heterozygous state in the proposita only. F8 gene polymorphism analysis indicated that the mutation must have occurred de novo in the paternal germline. Furthermore, analysis of the pattern of X chromosome methylation at the human androgen receptor gene locus demonstrated a skewed inactivation of the derived maternal X chromosome from the lymphocytes of the proband's DNA. Thus, the severe hemophilia A in the proposita results from a de novo F8 gene frameshift-stop mutation on the paternally derived X chromosome, associated with a nonrandom pattern of inactivation of the maternally derived X chromosome. (Blood. 2000;96:4373-4375)

[Avellino dystrophy. Current diagnostic criteria]

We report a French family suffering from an Avellino corneal dystrophy diagnosed by using clinical, histological, ultrastructural and genetics findings. Our results indicate that direct corneal examination and routine histological examinations must always be associated with an assay for BIGH3 gene mutations to establish a modern and unambiguous diagnosis of a corneal dystrophy.

Clinical, histologic, and ultrastructural features of the corneal dystrophy caused by the R124L mutation of the BIGH3 gene

OBJECTIVE

This study was designed to describe the clinical, histologic, and ultrastructural features of the corneal dystrophy associated with the R124L mutation of the BIGH3 gene.

DESIGN

Retrospective clinical and histologic review of a new genetic mutation.

PARTICIPANTS

Thirty-four patients from five unrelated French families with corneal dystrophy caused by the R124L mutation of the BIGH3 gene were studied at the clinical, histologic, and ultrastructural levels. Records of patients carrying this mutation were compared with those from three unrelated patients with corneal dystrophy of Bowman's layer (CDB) type 2 (R555Q mutation) and from three unrelated patients with classic corneal granular dystrophy (R555W mutation).

INTERVENTION

The mutational genetic status of the BIGH3 gene was determined for each patient, and the histologic and ultrastructural data available after corneal graft were analyzed.

MAIN OUTCOMES MEASURES

Genomic DNA was extracted from peripheral blood leukocytes. Exons 4 and 12 of the BIGH3 gene were amplified by the polymerase chain reaction (PCR), and the PCR products were directly sequenced.

RESULTS

All 34 patients with the R124L mutation displayed the clinical, histologic, and electron microscopic features of the dystrophy previously described as a superficial variant of corneal granular dystrophy. Combining molecular genetics with clinical and histologic findings established a clear distinction between the R555Q and R555W dystrophies.

CONCLUSIONS

The R124L mutation of the BIGH3 gene is associated with specific clinical and morphologic criteria. This indicates that molecular studies are needed for an adequate classification of corneal dystrophies. All criteria are presently available to segregate the dystrophy caused by the R124L mutation (known as CDB1) from the dystrophy caused by the R555Q mutation (known as CDB2).

[Diagnostic strategy in amyloidosis]

INTRODUCTION

The diagnosis of amyloidosis is a four-step strategy requiring: 1) a high degree of suspicion, as the clinical presentation of the disease is very polymorphous; 2) the biochemical nature of the disease; 3) the evaluation of the disease spread and 4) how it evolves.

EXEGESIS

Simple and noninvasive biopsies usually make it possible to diagnose amyloidosis. Available treatments of generalized amyloidosis require an exact characterization of the nature of amyloid deposits, which is based on the clinical context, immunohistochemical analysis of amyloid deposits, and genetic testing.

CONCLUSION

Management of amyloidosis should be improved by better characterization of amyloid deposits. This would result in epidemiological data which are currently lacking.

A novel variant of granular corneal dystrophy caused by association of 2 mutations in the TGFBI gene-R124L and DeltaT125-DeltaE126

OBJECTIVE

To characterize the molecular defect in the TGFBI gene in a French family affected with an atypical granular corneal dystrophy.

PATIENTS

This family comprises 9 affected individuals across 3 generations without consanguineous marriage.

METHODS

Light and electron microscopy were used to examine corneal buttons from patients. Exons of the TGFBI gene were amplified by polymerase chain reaction and sequenced directly using an automated method. Restriction digestion analysis and heteroduplex screening were performed to confirm that the mutations identified were not polymorphisms.

RESULTS

Round or snow-flakes-like deposits that stained red with Masson trichrome and appeared as dense, rod-shaped structures were observed in the most anterior layers of the central stroma. All patients were heterozygous for the R124L mutation and a novel mutation predicting the deletion of 2 amino acid residues-threonine (T) and glutamic acid (E)-at codons 125 and 126.

CONCLUSIONS

This French family is affected with a novel variant of granular dystrophy that is caused by a molecular defect in the TGFBI gene, reported here for the first time.

CLINICAL RELEVANCE

These 2 mutations cause a novel variant of granular dystrophy that is intermediate in severity between the classical and superficial variant forms. Arch Ophthalmol. 2000;118:814-818

A new mutation (A546T) of the betaig-h3 gene responsible for a French lattice corneal dystrophy type IIIA

PURPOSE

To characterize the betaig-h3 gene defect in a French family affected with lattice corneal dystrophy type IIIA (LCDIIIA).

METHODS

Histologic examination was performed from corneal buttons of two patients. Genomic DNA was extracted from leukocytes, and exons of the betaig-h3 gene were amplified by polymerase chain reaction to be directly sequenced.

RESULTS

Numerous deposits were evident in the stroma and beneath the Bowman membrane, which had all the features of amyloid deposits. Analysis of exon 12 revealed a heterozygous G to A transition on codon 546.

CONCLUSION

In contrast to Japanese patients, these French patients affected with LCDIIIA carry a distinct mutation of the betaig-h3 gene (A546T instead of P501T). Therefore, it is unclear whether different mutations could result in the same dystrophy or whether we are dealing with clinical heterogeneity of LCDIIIA.

Expression of human F8B, a gene nested within the coagulation factor VIII gene, produces multiple eye defects and developmental alterations in chimeric and transgenic mice

Factor VIII-associated gene B ( F8B ) is a small human gene of unknown function which is nested within the gene encoding coagulation factor VIII ( FVIII ) in chromosome band Xq28. The sequence of F8B includes the C2 cell adhesion motif of factor VIII, which has also been identified in numerous proteins known to play important roles during development. Here we have constructed both chimeric and transgenic mice expressing normal human F8B to investigate its possible developmental effects. The chimeras produced from embryonic stem cells transfected with normal F8B under control of a cytomegalovirus promoter and selected for neomycin resistance expressed readily detectable levels of F8B mRNA in multiple tissues. They showed growth retardation, microcephaly, reduced longevity and severe ocular defects, and although they were fertile, gave birth to no F8B heterozygous pups. Seven transgenic mouse lines, produced by injection of the transgene into fertilized oocytes, were viable and of normal size but expressed lower levels of F8B mRNA. Strikingly, they showed the same severe eye abnormalities as the chimeras. These defects included anterior segment dysgenesis, absent or abnormal lens, persistence of the primary vitreous, Harderian gland tumors and ectopic pigmented cells, suggesting that migration of neural crest cells might have been perturbed during eye development. In addition, dysplastic retinas and the absence of photoreceptors were observed, providing a mouse model for retinal degeneration.

Prevalence, male germ-line origin and new patterns of inversions in haemophilia A

Following the discovery of the FVIII gene inversion by Lakich et al. [1] and Naylor et al. [2], we have investigated this mutation in 108 French and Algerian severe haemophilia A patients. We have found that only 29 severe haemophiliacs (27%) exhibited the rearrangement whereas Lakich et al. [1] and Naylor et al. [2] respectively estimated the inversion frequency at 47% and 42% in severe haemophiliacs. The reason for this discrepancy is not accounted for. In this study, we observed two novel patterns of inversions as yet unreported. We did not find any correlation between the presence of the inversion and a particular RLFP haplotype, or ethnic origin, or the absence of a FVIII inhibitor. Among the cases with the inversion, the proportion of sporadic and transmitted cases was roughly equivalent and we also confirm that the inversion occurs preferentially in the male germ-line.

Spectrum of growth hormone receptor mutations and associated haplotypes in Laron syndrome

Laron syndrome is a rare autosomal recessive disorder characterized by resistance to growth hormone (GH). In 10 patients of different ethnic origins, we have analyzed all the GH receptor (GHR)-coding exons along with their splice junctions and 6 intragenic polymorphic sites defining several GHR gene haplotypes. This allowed us to identify the mutations in the 20 chromosomes studied and to describe a new GHR haplotype. Eleven different mutations associated with various GHR haplotypes were observed; they included 3 nonsense mutations, 3 splice defects and 5 missense mutations. Of the 11 mutations, 8 were novel. All the mutations involved the exoplasmic domain of the receptor and all the missense mutations were clustered in a short polypeptide segment. Most of the missense mutations affected residues conserved among GHRs from different species and the related molecules that belong to the cytokine receptor superfamily. Adding to the 5 mutations so far described, these findings illustrate the allelic heterogeneity of this syndrome and document the independent origin of the molecular defects, all features of clinical relevance for genetic counselling.