Two pedigrees segregating Duane's retraction syndrome as a dominant trait map to the DURS2 genetic locus

CHN1 is a Novel Prognostic Marker for Diffuse Large B-Cell Lymphoma

Purpose

Diffuse large B-cell lymphoma (DLBCL) is the most common B-cell malignancy. Thirty to forty percent of DLBCL patients still experience relapse or develop refractory disease even with standard immunochemotherapy, leading to a poor prognosis. Currently, although several gene-based classification methods can be used to predict the prognosis of DLBCL, some patients are still unable to be classified. This study was performed to identify a novel prognostic biomarker for DLBCL.

Patients and Methods

A total of 1850 B-cell non-Hodgkin lymphoma (B-NHL) patients in 8 independent datasets with microarray gene expression profiles were retrieved from the Gene Expression Omnibus (GEO) database and Lymphoma/Leukemia Molecular Profiling Project (LLMPP). The candidate genes were selected through three filters in a strict pipeline. Survival analysis was performed in two independent datasets of patients with both gene expression data and clinical information. Gene set enrichment analysis (GSEA) and the CIBERSORT algorithm were used to explore the biological functions of the genes.

Results

We identified 6 candidate genes associated with the clinical outcome of DLBCL patients: CHN1, CD3D, CLU, ICOS, KLRB1 and LAT. Unlike the other five genes, CHN1 has not been previously reported to be implicated in lymphoma. We also observed that CHN1 had prognostic significance in important clinical subgroups; in particular, high CHN1 expression was significantly related to good outcomes in DLBCL patients with the germinal center B-cell-like (GCB) subtype, stage III–IV, or an International Prognostic Index (IPI) score > 2. Multivariate Cox regression analysis of the two datasets showed that CHN1 was an independent prognostic factor for DLBCL. Additionally, GSEA and CIBERSORT indicated that CHN1 was correlated with cell adhesion and T cell immune infiltration.

Conclusion

Our data indicate for the first time that high CHN1 expression is associated with favorable outcomes in DLBCL patients, suggesting its potential utility as a prognostic marker in DLBCL.

CHN1 gene mutation analysis in patients with Duane retraction syndrome

PURPOSE

To investigate CHN1 (chimerin 1) gene mutations in patients with isolated nonsyndromic Duane syndrome and accompanying positive familial history, bilaterality, or various systemic disorders.

METHODS

Patients with Duane retraction syndrome (DRS) and a positive family history of congenital ocular motility disturbance or bilateral involvement or accompanying any congenital disorder(s) seen consecutively at a single center from 2013 to 2016 were enrolled. All subjects underwent full ophthalmologic examination, including refraction, best-corrected visual acuity, ocular alignment and motility, globe retraction, and biomicroscopic or fundus evaluation. DNA samples were investigated by direct sequencing of the coding regions of the CHN1 gene.

RESULTS

A total of 30 patients (15 males) were included (mean age, 11.8 ± 10.4 years; range, 2-45 years): 8 cases presented with bilateral DRS; 22, with unilateral DRS. Family history of ocular motility abnormality was positive in 16 patients. Eleven cases had an additional congenital disorder. In 2 patients, 2 different mutations were detected in the CHN1 gene: p.E313K (c.937G>A) and p.N224S (c.671A>G).

CONCLUSIONS

CHN1 mutations were identified in 2 bilateral cases and in 1 parent of 1 affected case. One mutation is novel and occurred with additional vertical gaze abnormalities. Additional genetic studies evaluating chimerin 1 (CHN1) and its role in the development of the ocular motor axis are needed to provide new data about these mutations and phenotypic variations.

The genetic basis of incomitant strabismus: consolidation of the current knowledge of the genetic foundations of disease

In recent years, our understanding of the genetic foundations of incomitant strabismus has grown significantly. Much new understanding has been gleaned since the concept of congenital cranial dysinnervation disorders (CCDDs) was introduced in 2002, and the genetic basis of CCDDs continues to be elucidated. In this review, we aim to provide an update of the genetic and clinical presentation of these disorders. Disorders reviewed include Duane syndrome (DS), HOXA1 and HOXB1 syndromes, Moebius syndrome, congenital fibrosis of the extraocular muscles (CFEOM), and horizontal gaze palsy with progressive scoliosis (HGPPS).

Intrinsic properties guide proximal abducens and oculomotor nerve outgrowth in avian embryos

Proper movement of the vertebrate eye requires the formation of precisely patterned axonal connections linking cranial somatic motoneurons, located at defined positions in the ventral midbrain and hindbrain, with extraocular muscles. The aim of this research was to assess the relative contributions of intrinsic, population-specific properties and extrinsic, outgrowth site-specific cues during the early stages of abducens and oculomotor nerve development in avian embryos. This was accomplished by surgically transposing midbrain and caudal hindbrain segments, which had been pre-labeled by electroporation with an EGFP construct. Graft-derived EGFP+ oculomotor axons entering a hindbrain microenvironment often mimicked an abducens initial pathway and coursed cranially. Similarly, some EGFP+ abducens axons entering a midbrain microenvironment mimicked an oculomotor initial pathway and coursed ventrally. Many but not all of these axons subsequently projected to extraocular muscles that they would not normally innervate. Strikingly, EGFP+ axons also took initial paths atypical for their new location. Upon exiting from a hindbrain position, most EGFP+ oculomotor axons actually coursed ventrally and joined host branchiomotor nerves, whose neurons share molecular features with oculomotor neurons. Similarly, upon exiting from a midbrain position, some EGFP+ abducens axons turned caudally, elongated parallel to the brainstem, and contacted the lateral rectus muscle, their originally correct target. These data reveal an interplay between intrinsic properties that are unique to oculomotor and abducens populations and shared ability to recognize and respond to extrinsic directional cues. The former play a prominent role in initial pathway choices, whereas the latter appear more instructive during subsequent directional choices.

Ocular manifestations (strabismus: duane syndrome; and retinal nerve fiber hypoplasia) in okihiro syndrome (duane radial ray syndrome)

BACKGROUND AND PURPOSE

Two siblings diagnosed with Okihiro Syndrome (also named Duane Radial Ray Syndrome) associated with ophthalmic manifestation including Duane Syndrome and retinal nerve fiber layer (RNFL) hypoplasia were presented.

METHODS

The first patient (15-years old female) was diagnosed of Duane Syndrome presenting reduction of visual acuity and pale optic discs. She showed a diffuse decrease in the RNFL thickness, mainly in her left eye, retaining the typical RNFL morphology as double hump, demonstrated by OCT and scanning laser polarimetry. Neurophysiology evaluation found a decrease in visual evoked potentials and pattern electroretinogram amplitudes, and an increase of the latency of P100 component. The second patient (12 year-old female) presented with Duane malformation. Both patients underwent a complete ophthalmic evaluation with best corrected visual acuity, visual field examination, optical coherence tomography (OCT), scanning laser polarimetry, visual evoked potentials, pattern electroretinogram, and genetic study.

RESULTS

The neuro-ophthalmic evaluation showed a subclinical reduction of RNFL average thickness provided by OCT and an increase of P50 and N95 latency by pattern electroretinogram. RNFL average thickness presented a score reduction in both patients, without typical glaucomatous morphology.

CONCLUSIONS

Our analyses suggest that Okihiro Syndrome may affect retinal nerve fiber layer development and visual acuity.

Expansion of the CHN1 strabismus phenotype

PURPOSE

Hyperactivating CHN1 mutations have been described in individuals with Duane retraction syndrome with or without vertical gaze abnormalities. This was a study of five family members with distinctive ocular dysmotility patterns that co-segregated with a novel hyperactivating CHN1 mutation.

METHODS

Participating members of a family segregating pleomorphic incomitant strabismus underwent ophthalmic examinations, and several underwent high-resolution magnetic resonance imaging (MRI) of the orbits and brain stem. Participant DNA was extracted and amplified for haplotype analysis encompassing the CHN1 region on chromosome 2q31.1, and mutation analysis of the CHN1 gene, which encodes the Rac-GAP signaling protein α2-chimaerin. In vitro functional studies of the co-inherited mutation were performed, including a Rac-GTP activation assay, quantification of α2-chimaerin translocation, and co-immunoprecipitation.

RESULTS

All five clinically affected family members exhibited monocular or binocular supraduction deficits, three in the absence of Duane retraction syndrome. MRI in four affected individuals demonstrated small or absent abducens nerves in all four, small oculomotor nerve in one, and small optic nerves in three. Superior oblique muscle volume was also decreased in three of the individuals, supporting trochlear nerve hypoplasia. Strabismus segregated with the CHN1 locus and affected individuals harbored a c.443A>T CHN1 mutation (p.Y148F). In vitro, this novel mutation behaved similarly to previously reported CHN1 mutations underlying familial Duane syndrome, hyperactivating α2-chimaerin by enhancing its dimerization and membrane association and lowering total intracellular Rac-GTP.

CONCLUSIONS

Analysis of the current pedigree expands the phenotypic spectrum of hyperactivating CHN1 mutations to include vertical strabismus and supraduction deficits in the absence of Duane retraction syndrome.

Two novel CHN1 mutations in 2 families with Duane retraction syndrome

OBJECTIVE

To determine the genetic cause of Duane retraction syndrome (DRS) in 2 families segregating DRS as a dominant trait.

METHODS

Members of 2 unrelated pedigrees were enrolled in a genetic study. Linkage analysis was performed on the CHN1 locus. Probands and family members were screened for CHN1 mutations.

RESULTS

The 6 affected individuals in the 2 pedigrees have DRS. Both pedigrees are consistent with linkage to the locus. Sequence analysis revealed 2 novel heterozygous missense CHN1 mutations, c.422C>T and c.754C>T, predicted to result in α2-chimaerin amino acid substitutions P141L and P252S, respectively.

CONCLUSIONS

Genetic analysis of 2 pedigrees revealed 2 novel DRS mutations, bringing the number of DRS pedigrees known to harbor CHN1 from 7 to 9. Both mutations alter residues that participate in intramolecular interactions that stabilize the inactive, closed conformation of α2-chimaerin and, thus, are predicted to result in its hyperactivation. Moreover, amino acid residue P252 was previously reported to be altered to a different residue in a previously reported DRS pedigree; thus, this is the first report of 2 CHN1 mutations altering the same residue, further supporting a gain-of-function etiology.

CLINICAL RELEVANCE

Members of families segregating DRS as an autosomal dominant trait should be screened for mutations in the CHN1 gene, enhancing genetic counseling and permitting earlier diagnosis.

Duane syndrome in the setting of chromosomal duplications

PURPOSE

To describe the clinical findings in 3 patients with Duane syndrome and 3 different chromosomal duplications that may indicate the location of genes involved in the pathogenesis of this ocular motility disorder.

DESIGN

Observational case series.

METHODS

setting: Clinical practice. patient or study population: Three patients with Duane syndrome and chromosomal duplications from the clinical practice of 1 of the authors. observation procedures: Chart review and retrieval of clinical data and results of pertinent clinical tests, in this case chromosomal studies. main outcome measure: Reporting of details of clinical findings and duplicated chromosomal regions.

RESULTS

Two patients had unilateral type I Duane syndrome and 1 had bilateral type I Duane syndrome. Two had cognitive delay, and all 3 had other systemic abnormalities, including a variety of congenital malformations. The chromosomal abnormalities that were detected using microarray analysis were 2q13(RP11-20G1,RP11-461N11) × 3, 10q24.2q26.3(101,532,585-135,284, 169) × 3, 20q13.12(44,796,613-44,945, 818) × 3, and 22q11.1q11.22(RP11-701M12, RP11-71G19) × 3.

CONCLUSIONS

Patients with Duane syndrome and associated congenital malformations or developmental delay should be evaluated for the presence of underlying chromosomal duplications. The regions of chromosomes 2, 10, and 22 that we report may harbor genes involved in the pathogenesis of Duane syndrome.

Review of the major findings about Duane retraction syndrome (DRS) leading to an updated form of classification

In view of all the reported evidence by electromyography in the 1970s, by histology in the 1980s, and by cerebral imagery since the 2000s, Duane retraction syndrome (DRS) has been described as the consequence of a congenital anomaly of the 6th cranial nerve nuclei with aberrant innervations by supply from the 3rd cranial nerve. Both genetic and environmental factors are likely to play a role when the cranial nerves and ocular muscles are developing between the 4th and the 8th week of gestation. New data from eye movement recordings contributed to better understanding the binocular control of saccades. Modeling of saccades in DRS seems promising for the quantification of the innervational deficit and the mechanical properties of the eye plant. The usual clinical classification of DRS needs to be updated in order to match more accurately the underlying dysinnervation of the extra ocular muscles and to illustrate the continuum that exists between the various forms. This review aims to summarize the major findings about DRS and to guide the clinician in the surgical management of this particular form of strabismus.

Distinctive clinical features of bilateral Duane retraction syndrome

PURPOSE

To compare the clinical characteristics of unilateral and bilateral forms of Duane retraction syndrome.

METHODS

A retrospective chart review of patients with Duane syndrome over a 10-year span was performed. All participants underwent a complete medical and ophthalmologic examination at the time of diagnosis. Data collected included the following: sex, age at first visit, form (unilateral/bilateral), side, type, ocular duction and version, abnormal head position, best-corrected visual acuity, refractive errors, presence of strabismus, binocular function, and associated congenital anomalies.

RESULTS

Of 94 patients identified, 17% were bilaterally affected. Of the bilateral patients, 12% had familial antecedents; 87.5% had the same type in both eyes with 75% bilateral type 1. Patients with bilateral Duane syndrome had significantly different visual acuity (mean, 0.1214 logMar vs 0.0035; p = 0.045), abnormal head position (56.25% vs 89%; p = 0.04), A or V patterns (69% vs 27.6%; p = 0.003), and associated congenital anomalies (50% vs 14%; p = 0.003) than patients with unilateral disease. There was also a suggestion of higher rates of ametropia, global vertical dysfunction, and abnormal stereoacuity in bilateral Duane syndrome that were not statistically significant.

CONCLUSIONS

Patients with bilateral Duane syndrome had lower visual acuity, a lower incidence of abnormal head posture, and a higher incidence of A or V patterns and associated congenital anomalies. Bilateral Duane retraction syndrome seems to involve multiple instances of deinnervation and fibrosis, resulting in horizontal and vertical oculomotor deficits and functional impairments.

A developmental and genetic classification for midbrain-hindbrain malformations

Advances in neuroimaging, developmental biology and molecular genetics have increased the understanding of developmental disorders affecting the midbrain and hindbrain, both as isolated anomalies and as part of larger malformation syndromes. However, the understanding of these malformations and their relationships with other malformations, within the central nervous system and in the rest of the body, remains limited. A new classification system is proposed, based wherever possible, upon embryology and genetics. Proposed categories include: (i) malformations secondary to early anteroposterior and dorsoventral patterning defects, or to misspecification of mid-hindbrain germinal zones; (ii) malformations associated with later generalized developmental disorders that significantly affect the brainstem and cerebellum (and have a pathogenesis that is at least partly understood); (iii) localized brain malformations that significantly affect the brain stem and cerebellum (pathogenesis partly or largely understood, includes local proliferation, cell specification, migration and axonal guidance); and (iv) combined hypoplasia and atrophy of putative prenatal onset degenerative disorders. Pertinent embryology is discussed and the classification is justified. This classification will prove useful for both physicians who diagnose and treat patients with these disorders and for clinical scientists who wish to understand better the perturbations of developmental processes that produce them. Importantly, both the classification and its framework remain flexible enough to be easily modified when new embryologic processes are described or new malformations discovered.

Clinical features associated with an I126M alpha2-chimaerin mutation in a family with autosomal-dominant Duane retraction syndrome

PURPOSE

We describe the clinical phenotype of a Mexican family segregating Duane syndrome as an autosomal-dominant trait linked to chromosome 2q31 (DURS2) and previously reported to harbor a heterozygous alpha2-chimaerin missense mutation.

METHODS

A 5-generation Mexican family was analyzed. Ten affected subjects were available for clinical examination. Participating subjects were tested for visual acuity, ocular alignment by prism cover testing, ocular ductions and versions, and globe retraction. In children, alignment was measured with the Krimsky test in cardinal positions of gaze.

RESULTS

Ten cases were included, 6 female and 4 male subjects. Five cases presented with bilateral and 5 with unilateral Duane syndrome. The right side was the most commonly affected side on unilateral cases. Five cases exhibited exotropia, 4 esotropia, and 1 hypotropia. Seven patients had severe limitation of abduction and two had moderate limitation. Four patients had mild adduction limitation and 4 had moderate limitation. No additional anomalies such as fourth (trochlear) nerve palsy, blepharoptosis, or dense amblyopia, which have been reported in previous families with Duane syndrome, were observed. All 3 cases that exhibited vertical dysfunction had upgaze limitation. One instance of nonpenetrance was recorded.

CONCLUSIONS

Considerable intrafamilial clinical variability was observed in this Duane syndrome pedigree that carried a alpha2-chimaerin mutation. The presence of bilateral involvement and associated vertical movements, which commonly are observed in this and other DURS2 families, could suggest the occurrence of CHN1 mutations as the source of the disease in isolated or familial DURS cases.

Familial unilateral Brown syndrome

We present a two-generation family with Brown syndrome. The proband was a six and a half-year-old female who presented with a history of failure of dextro-elevation of her left eye. A full ophthalmic evaluation was consistent with a left Brown syndrome. Family history revealed that her mother was operated on as a child for left Brown syndrome and examination of her four and a half-year-old sibling showed similar affection in the left eye. Autosomal dominant inheritance has been postulated in this condition. To our knowledge this is the first report of three members of a two-generation family with left-sided Brown syndrome. Genetic counseling of Brown syndrome cases is advised; nevertheless, identification of the responsible gene should shed more light on its genetics.

Human CHN1 mutations hyperactivate alpha2-chimaerin and cause Duane's retraction syndrome

Duane's retraction syndrome (DRS) is a complex congenital eye movement disorder caused by aberrant innervation of the extraocular muscles by axons of brainstem motor neurons. Studying families with a variant form of the disorder (DURS2-DRS), we have identified causative heterozygous missense mutations in CHN1, a gene on chromosome 2q31 that encodes alpha2-chimaerin, a Rac guanosine triphosphatase-activating protein (RacGAP) signaling protein previously implicated in the pathfinding of corticospinal axons in mice. We found that these are gain-of-function mutations that increase alpha2-chimaerin RacGAP activity in vitro. Several of the mutations appeared to enhance alpha2-chimaerin translocation to the cell membrane or enhance its ability to self-associate. Expression of mutant alpha2-chimaerin constructs in chick embryos resulted in failure of oculomotor axons to innervate their target extraocular muscles. We conclude that alpha2-chimaerin has a critical developmental function in ocular motor axon pathfinding.

Magnetic resonance imaging of innervational and extraocular muscle abnormalities in Duane-radial ray syndrome

PURPOSE

The authors used magnetic resonance imaging (MRI) to study extraocular muscles (EOMs) and nerves in Duane-radial ray (Okihiro) syndrome (DRRS) caused by mutations in the transcription factor SALL4.

METHODS

The authors examined four male and two female affected members of a pedigree previously reported to cosegregate DRRS and a heterozygous SALL4 mutation. Coronal T1-weighted magnetic resonance images of the orbits and heavily T2-weighted images in the plane of the cranial nerves were obtained in four subjects. MRI findings were correlated with motility examinations and published norms obtained using identical technique.

RESULTS

Five of the six subjects with DRRS had radial ray abnormalities including thumb, radial artery, radial bone, and pectoral muscle hypoplasia. Three had bilateral and three had unilateral ocular involvement. Seven eyes had limitation of both abduction and adduction, whereas two had limitations only of abduction. Most affected eyes had lid fissure narrowing and retraction in adduction. Intraorbital and intracranial abducens nerves (CN6) were small to absent, particularly ipsilateral to abduction deficiency. All subjects undergoing MRI had normal intracranial oculomotor nerves (CN3). Optic nerve (ON) cross-section findings were similar to normal. EOMs and pulleys were structurally normal in most subjects. In some affected orbits, a branch of CN3 closely approximated and presumably innervated the LR.

CONCLUSIONS

DRRS encompasses a Duane syndrome phenotype, with a variable and asymmetric endophenotype including marked CN6 hypoplasia and probable innervation or coinnervation of the LR by CN3. This endophenotype is more limited than reported in DURS2-linked Duane syndrome (On-line Mendelian Inheritance in Man, OMIM 604356) and CFEOM1 (OMIM 135700), which are clinically similar congenital cranial dysinnervation disorders that also feature CN3 hypoplasia and more widespread EOM abnormalities.

Clinical characterization of the HOXA1 syndrome BSAS variant

BACKGROUND

The Bosley-Salih-Alorainy syndrome (BSAS) variant of the congenital human HOXA1 syndrome results from autosomal recessive truncating HOXA1 mutations. We describe the currently recognized spectrum of ocular motility, inner ear malformations, cerebrovascular anomalies, and cognitive function.

METHODS

We examined nine affected individuals from five consanguineous Saudi Arabian families, all of whom harbored the same I75-I76insG homozygous mutation in the HOXA1 gene. Patients underwent complete neurologic, neuro-ophthalmologic, orthoptic, and neuropsychological examinations. Six individuals had CT, and six had MRI of the head.

RESULTS

All nine individuals had bilateral Duane retraction syndrome (DRS) type 3, but extent of abduction and adduction varied between eyes and individuals. Eight patients were deaf with the common cavity deformity of the inner ear, while one patient had normal hearing and skull base development. Six had delayed motor milestones, and two had cognitive and behavioral abnormalities meeting Diagnostic and Statistical Manual of Mental Disorders-IV criteria for autism spectrum disorder. MRI of the orbits, extraocular muscles, brainstem, and supratentorial brain appeared normal. All six appropriately studied patients had cerebrovascular malformations ranging from unilateral internal carotid artery hypoplasia to bilateral agenesis.

CONCLUSIONS

This report extends the Bosley-Salih-Alorainy syndrome phenotype and documents the clinical variability resulting from identical HOXA1 mutations within an isolated ethnic population. Similarities between this syndrome and thalidomide embryopathy suggest that the teratogenic effects of early thalidomide exposure in humans may be due to interaction with the HOX cascade.

Magnetic resonance imaging evidence for widespread orbital dysinnervation in dominant Duane's retraction syndrome linked to the DURS2 locus

PURPOSE

High-resolution, multipositional magnetic resonance imaging (MRI) was used to demonstrate extraocular muscles (EOMs) and associated motor nerves in Duane retraction syndrome (DRS) linked to the DURS2 locus on chromosome 2.

METHODS

Five male and three female affected members of two autosomal dominant DURS2 pedigrees were enrolled in the study. Coronal T(1)-weighted MRI of the orbits was obtained in multiple gaze positions, as well as with heavy T(2) weighting in the plane of the cranial nerves. MRI findings were correlated with motility.

RESULTS

All subjects had unilateral or bilateral limitation of abduction, or of both abduction and adduction, with palpebral fissure narrowing and globe retraction in adduction. Orbital motor nerves were typically small, with the abducens nerve (cranial nerve [CN]6) often nondetectable. Lateral rectus (LR) muscles were structurally abnormal in seven subjects, with structural and motility evidence of oculomotor nerve (CN3) innervation from vertical rectus EOMs leading to A or V patterns of strabismus in three cases. Four cases had superior oblique, two cases superior rectus, and one case levator EOM hypoplasia. Only the medial and inferior rectus and inferior oblique EOMs were spared. Two cases had small CN3s.

CONCLUSIONS

DRS linked to the DURS2 locus is associated with bilateral abnormalities of many orbital motor nerves, and structural abnormalities of all EOMs except those innervated by the inferior division of CN3. The LR may be coinnervated by CN3 branches normally destined for any other rectus EOMs. Therefore, DURS2-linked DRS is a diffuse congenital cranial dysinnervation disorder involving but not limited to CN6.