Germ-line NF2 mutations and disease severity in neurofibromatosis type 2 patients with retinal abnormalities

Gene Therapy for Neurofibromatosis Type 2-Related Schwannomatosis: Recent Progress, Challenges, and Future Directions

Neurofibromatosis type 2 (NF2)-related schwannomatosis is a rare autosomal dominant monogenic disorder caused by mutations in the NF2 gene. The hallmarks of NF2-related schwannomatosis are bilateral vestibular schwannomas (VS). The current treatment options for NF2-related schwannomatosis, such as observation with serial imaging, surgery, radiotherapy, and pharmacotherapies, have shown limited effectiveness and serious complications. Therefore, there is a critical demand for novel effective treatments. Gene therapy, which has made significant advancements in treating genetic diseases, holds promise for the treatment of this disease. This review covers the genetic pathogenesis of NF2-related schwannomatosis, the latest progress in gene therapy strategies, current challenges, and future directions of gene therapy for NF2-related schwannomatosis.

Structural Abnormalities of the Central Retina in Neurofibromatosis Type 2

INTRODUCTION

This case-control study seeks to systematically characterize the central retinal findings in a large cohort of patients with neurofibromatosis type 2 (NF2) using spectral domain optical coherence tomography (SD-OCT) as well as the examination of the potential use of this technique as a diagnostic tool in NF2.

METHODS

Fifty-four patients with an NF2 diagnosis seen in a quaternary national service were age- and gender-matched to 55 controls from the normal population. Two masked assessors categorized SD-OCT images using predefined abnormalities: retinal tufts, epiretinal membrane (ERM) appearance, retinal hamartoma, and foveal contour. Specificity, sensitivity, and positive and negative predictive values were calculated for each retinal abnormality. Trends of retinal abnormalities with NF2 genetic severity groups (1. tissue mosaic; 2A. mild classic; 2B. moderate classic; and 3. severe) were investigated.

RESULTS

We found retinal abnormalities in 26 patients with NF2 (48%) and 2 control patients (4%); retinal tufts were the most common abnormality therein (43%) and were not seen in controls. The specificity and sensitivity of the graded abnormalities on OCT scans in NF2 were 96% and 48%, respectively, with a positive predictive value of 93%. In our cohort, retinal tufts had a specificity of 100%, a sensitivity of 43%, and a positive predictive value of 100%. Retinal hamartomas were seen only in NF2 patients (35% sensitivity and 100% specificity). ERMs had 96% specificity and 13% sensitivity. The proportion of patients with retinal abnormalities increased statistically significantly with NF2 genetic severity; all patients within the 3. severe genetic severity had an abnormal SD-OCT.

DISCUSSION/CONCLUSION

We present a systematic study of central retinal abnormalities in an NF2 population as seen on SD-OCT imaging. Our results show a high frequency of retinal abnormalities that are readily detected by SD-OCT imaging. The presence of retinal tufts may be a novel marker of NF2 with both high specificity and a positive predictive value for NF2, compared to other well-known ocular features of NF2, and may have a place in the NF2 diagnostic criteria.

Hippo-yap signaling in ocular development and disease

The Hippo-Yes associated protein (Yap) pathway plays an important role in organ size control by regulating cell proliferation, apoptosis, and stem cell renewal. Hippo-Yap signaling also functions at the level of cellular development in a variety of organs through its effects on cell cycle control, cell survival, cell polarity, and cell fate. Because of its important roles in normal development and homeostasis, abnormal regulation of this pathway has been shown to lead to pathological outcomes such as tissue overgrowth, tumor formation, and abnormal organogenesis, including ocular-specific disorders. In this review, we summarize how normal and perturbed control of Yap signaling is implicated in ocular development and disease Developmental Dynamics 247:794-806, 2018. © 2018 Wiley Periodicals, Inc.

Differential Expression of NF2 in Neuroepithelial Compartments Is Necessary for Mammalian Eye Development

The optic neuroepithelial continuum of vertebrate eye develops into three differentially growing compartments: the retina, the ciliary margin (CM), and the retinal pigment epithelium (RPE). Neurofibromin 2 (Nf2) is strongly expressed in slowly expanding RPE and CM compartments, and the loss of mouse Nf2 causes hyperplasia in these compartments, replicating the ocular abnormalities seen in human NF2 patients. The hyperplastic ocular phenotypes were largely suppressed by heterozygous deletion of Yap and Taz, key targets of the Nf2-Hippo signaling pathway. We also found that, in addition to feedback transcriptional regulation of Nf2 by Yap/Taz in the CM, activation of Nf2 expression by Mitf in the RPE and suppression by Sox2 in retinal progenitor cells are necessary for the differential growth of the corresponding cell populations. Together, our findings reveal that Nf2 is a key player that orchestrates the differential growth of optic neuroepithelial compartments during vertebrate eye development.

[Type 2 neurofibromatosis: intergenerational differences in genetic and clinical expression]

INTRODUCTION

Neurofibromatosis type 2 (NF2) is a rare dominantly inherited disease. Its clinical presentation can be completely different in children and adults and early diagnosis is often difficult. The NF2 gene molecular analysis can help for diagnosis, but its result can be negative in case of NF2 mosaicism.

OBSERVATIONS

We report the case of a 43-year-old man who had developed a severe phenotype with bilateral vestibular schwannomas at 19 years of age. His son presented a retinal hamartoma with loss of vision in his right eye at 2 months of age. At 9 years of age, asymptomatic schwannomas of the cranial nerves were discovered: cranial nerves X (left), XI (left), and VIII (bilateral). Partial constitutional NF2 deletion (from exons 2-7) was detected in his son. The deletion was not detectable in the DNA blood of his father and we strongly suspect a mosaic form of NF2.

CONCLUSION

Ophthalmological manifestations can be the initial sign of NF2 in childhood. These features must be actively sought during the first year of life in individuals at risk of NF2. NF2 mosaicism is often described as a mild form of NF2 with a very low risk of transmission to the carrier's children. We show that NF2 mosaicism can sometimes develop severe NF2 symptoms and we confirm that the transmission risk to the offspring depends on the proportion of zygotes carrying the mutation. NF2 remains a life-limiting and life-spoiling condition. Early diagnosis is necessary to prevent complications and the follow-up of NF2 patients must be organized throughout life in specialty centers.

Neurofibromatosis type 2

Neurofibromatosis type 2 is an autosomal-dominant multiple neoplasia syndrome that results from mutations in the NF2 tumour suppressor gene located on chromosome 22q. It has a frequency of one in 25,000 livebirths and nearly 100% penetrance by 60 years of age. Half of patients inherit a germline mutation from an affected parent and the remainder acquire a de novo mutation for neurofibromatosis type 2. Patients develop nervous system tumours (schwannomas, meningiomas, ependymomas, astrocytomas, and neurofibromas), peripheral neuropathy, ophthalmological lesions (cataracts, epiretinal membranes, and retinal hamartomas), and cutaneous lesions (skin tumours). Optimum treatment is multidisciplinary because of the complexities associated with management of the multiple, progressive, and protean lesions associated with the disorder. We review the molecular pathogenesis, genetics, clinical findings, and management strategies for neurofibromatosis type 2.

Mutational spectrum of the NF2 gene: a meta-analysis of 12 years of research and diagnostic laboratory findings

The NF2 tumor suppressor gene on chromosome 22 is a member of the protein 4.1 family of cytoskeletal elements. A number of single- and multiple-tumor phenotypes have been linked to alterations of NF2 since its characterization in 1993. We present a meta-analysis of 967 constitutional and somatic NF2 alterations from 93 published reports, along with 59 additional unpublished events identified in our laboratory and 115 alterations identified in clinical samples submitted to the Massachusetts General Hospital (MGH) Neurogenetics DNA Diagnostic Laboratory. In total, these sources defined 1,070 small genetic changes detected primarily by exon scanning, 42 intragenic changes of one whole exon or larger, and 29 whole gene deletions and gross chromosomal rearrangements. Constitutional single-exon events (N=422) were significantly more likely to be nonsense or splice site changes than somatic events (N=533), which favored frameshift changes (chi(2) test; P<0.001). Somatic events also differed markedly between tumors of different pathology, most significantly in the tendency of somatic events in meningiomas to lie within the 5' FERM domain of the transcript (Fisher's exact test; P<0.01 in comparison to schwannomas) with a complete absence of mutations in exons 14 and 15. There was no statistically significant difference in mutation type or exon distribution between published constitutional events and those found by the clinical laboratory. Less than 10% of all published and unpublished small alterations are nontruncating (N=63) and these changes are clustered in exons 2 and 3, suggesting that this region may be especially crucial to tumor suppressor activity in the protein.

Neuro-ophthalmology of the phacomatoses

The phacomatoses are a group of disorders that feature multiple hamartomas of the central and peripheral nervous system, eye, skin, and viscera. Most of these disorders have a well-defined Mendelian pattern of inheritance because of a mutation in a single gene which has been identified. In other instances, no clear patterns of inheritance or genetic susceptibility have been recognized. The combination of ocular and central nervous system manifestations in patients with phacomatoses makes neuro-ophthalmologic evaluation particularly important in diagnosis and management. This review provides an overview of the phacomatoses with emphasis on recent reports of significance to neuro-ophthalmology.