Germline Mosaicism for KIF21A Mutation (p.R954L) Mimicking Recessive Inheritance for Congenital Fibrosis of the Extraocular Muscles

Phenotype, genotype, and management of congenital fibrosis of extraocular muscles type 1 in 16 Chinese families

PURPOSE

Congenital fibrosis of extraocular muscles type 1 (CFEOM1), a classical subtype of CFEOM, is characterized by restrictive ophthalmoplegia and ptosis. It is mainly caused by aberrant neural innervation of the extraocular muscles. This study aimed to investigate the genetic characteristics and clinical manifestations of CFEOM1 in Chinese families.

METHODS

The clinical data, including ocular examinations, magnetic resonance imaging (MRI), and surgical procedures of affected individuals from 16 Chinese CFEOM1 families, were collected. The genomic DNA of 16 probands and their family members were sequenced for causative KIF21A gene mutations. Linkage analysis using microsatellite markers across KIF21A was also conducted.

RESULTS

Affected individuals were presented with bilateral non-progressive ptosis, restricted horizontal eye movement, fixed infraduction of both eyes, compensatory chin-up head position, and neuromuscular abnormalities. Three heterozygous KIF21A mutations, c.2860C > T (p.R954W) (in eight families), c.2861G > T (p.R954L) (in two families), and c.2861G > A (p.R954Q) (in two families) were identified, which implied that hotspot mutations were common in Chinese CFEOM1 families. Germline Mosaicism was likely to be the cause of affected individuals with asymptomatic parents without KIF21A mutations presented in the eight families. Two affected individuals underwent modified levator muscle complex suspension surgery and achieved a good result without any complications.

CONCLUSION

Instead of evaluating the whole CFEOM1 gene variant, hotspot mutations could be given priority for screening. The occurrence of germline mosaicism has to be taken into account in genetic counseling. Patients with CFEOM1 who have ptosis may benefit from an innovative surgical procedure called modified levator muscle complex suspension.

Congenital Fibrosis of the Extraocular Muscles: An Overview from Genetics to Management

Congenital fibrosis of the extraocular muscles (CFEOM) is a genetic disorder belonging to the congenital cranial dysinnervation disorders and is characterized by nonprogressive restrictive ophthalmoplegia. It is phenotypically and genotypically heterogeneous. At least seven causative genes and one locus are responsible for the five subtypes, named CFEOM-1 to CFEOM-5. This review summarizes the currently available molecular genetic findings and genotype–phenotype correlations, as well as the advances in the management of CFEOM. We propose that the classification of the disorder could be optimized to provide better guidance for clinical interventions. Finally, we discuss the future of genetic-diagnosis-directed studies to better understand such axon guidance disorders.

Cytoskeleton saga: Its regulation in normal physiology and modulation in neurodegenerative disorders

Cells are fundamental units of life. To ensure the maintenance of homeostasis, integrity of structural and functional counterparts is needed to be essentially balanced. The cytoskeleton plays a vital role in regulating the cellular morphology, signalling and other factors involved in pathological conditions. Microtubules, actin (microfilaments), intermediate filaments (IF) and their interactions are required for these activities. Various proteins associated with these components are primary requirements for directing their functions. Disruption of this organization due to faulty genetics, oxidative stress or impaired transport mechanisms are the major causes of dysregulated signalling cascades leading to various pathological conditions like Alzheimer's (AD), Parkinson's (PD), Huntington's disease (HD) or amyotrophic lateral sclerosis (ALS), hereditary spastic paraplegia (HSP) or any traumatic injury like spinal cord injury (SCI). Novel or conventional therapeutic approaches may be specific or non-specific, targeting either three basic components of the cytoskeleton or various cascades that serve as a cue to numerous pathways like ROCK signalling or the GSK-3β pathway. An enormous number of drugs have been redirected for modulating the cytoskeletal dynamics and thereby may pave the way for inhibiting the progression of these diseases and their complications.

Prognostic value of Kinesin-4 family genes mRNA expression in early-stage pancreatic ductal adenocarcinoma patients after pancreaticoduodenectomy

BACKGROUND

The aim of this study was to investigate the potential prognostic value of Kinesin-4 family genes mRNA expression in early-stage pancreatic ductal adenocarcinoma (PDAC) patients after pancreaticoduodenectomy.

METHODS

Kaplan-Meier survival analysis method with log-rank test and Cox proportional hazards regression analysis were performed to figure out the association between Kinesin-4 family genes expression and PDAC patients overall survival time. Joint-effect survival analysis and stratified survival analysis were carried out to assess the prognosis prediction value of prognosis-related gene. Nomogram was constructed for the individualized prognosis prediction. In addition, we had used the gene set enrichment analysis and genome-wide co-expression analysis to further explore the potential mechanism.

RESULTS

KIF21A expression level was significantly associated with PDAC patient clinical prognosis outcome and patient with a high expression of KIF21A would have a shorter overall survival time. The prognosis prediction significance of KIF21A was well validated by the joint-effect survival analysis, stratified survival analysis, and nomogram. Meanwhile, the gene set enrichment analysis and genome-wide co-expression analysis revealed that KIF21A might involve in DNA damage and repair, transcription and translation process, post-translation protein modification, cell cycle, carcinogensis genes and pathways.

CONCLUSIONS

Our current research demonstrated that KIF21A could serve as a potential prognostic biomarker for patient with early-stage PDAC after pancreaticoduodenectomy.

Reconciling genotype with phenotype: Lessons learned on the Arabian Peninsula

On the Arabian Peninsula, where consanguineous/endogamous marriages are customary, hereditary eye disease is often autosomal recessive and genotype-phenotype correlation is typically straightforward. However, this is not always the case. Lessons I have learned in the course of reconciling genotype with phenotype in the region include the following: (1) although autosomal recessive disease is common, autosomal dominant disease still occurs; (2) an individual or family can be affected by more than one genetic eye disease; and (3) phenotype trumps genotype.

Surgical management of hypotropia in congenital fibrosis of extraocular muscles (CFEOM) presented by pseudoptosis

Purpose

To describe the demographics, characteristics, management pitfalls, and outcomes of pseudoptosis associated with congenital fibrosis of the extraocular muscles (CFEOM).

Methods

A retrospective review was performed of eight patients presenting with ptosis and hypotropia to oculoplastic service. All patients underwent full ocular evaluation and magnetic resonance imaging of brain and orbit. Five of these patients underwent stepwise correction of hypotropia by single-stage adjustable strabismus surgery (SSASS), followed by a frontalis sling if needed.

Results

Eight patients had congenital strabismus with severe ptosis and a positive forced duction test. There was a highly significant improvement from preoperative mean hypotropia angle of 30 prism diopters (PD) to 9 PD mean postoperative angle (P = 0.006). Surgery for ptosis was not needed in 80% of eyes.

Conclusion

CFEOM involving both ptosis and hypotropia could be properly managed with the correct sequence of surgical steps. Proper vertical alignment by correction of hypotropia utilizing SSASS may alleviate the need for ptosis surgery.

PATHOLOGIES OF AXONAL TRANSPORT IN NEURODEGENERATIVE DISEASES

Gene products such as organelles, proteins and RNAs are actively transported to synaptic terminals for the remodeling of pre-existing neuronal connections and formation of new ones. Proteins described as molecular motors mediate this transport and utilize specialized cytoskeletal proteins that function as molecular tracks for the motor based transport of cargos. Molecular motors such as kinesins and dynein's move along microtubule tracks formed by tubulins whereas myosin motors utilize tracks formed by actin. Deficits in active transport of gene products have been implicated in a number of neurological disorders. We describe such disorders collectively as "transportopathies". Here we review current knowledge of critical components of active transport and their relevance to neurodegenerative diseases.

Genetic linkage analysis in the presence of germline mosaicism

Germline mosaicism is a genetic condition in which some germ cells of an individual contain a mutation. This condition violates the assumptions underlying classic genetic analysis and may lead to failure of such analysis. In this work we extend the statistical model used for genetic linkage analysis in order to incorporate germline mosaicism. We develop a likelihood ratio test for detecting whether a genetic trait has been introduced into a pedigree by germline mosaicism. We analyze the statistical properties of this test and evaluate its performance via computer simulations. We demonstrate that genetic linkage analysis has high power to identify linkage in the presence of germline mosaicism when our extended model is used. We further use this extended model to provide solid statistical evidence that the MDN syndrome studied by Genzer-Nir et al. has been introduced by germline mosaicism.

Congenital fibrosis of the extraocular muscles

Background:

Congenital fibrosis of the extraocular muscles (CFEOM) describes a group of rare congenital eye movement disorders that result from the dysfunction of all or part of the oculomotor (CN 3) and the trochlear (CN 4) nerves, and/or the muscles these nerves innervate.

Aim:

To describe the clinical and neuro-radiological findings in three patients with CFEOM and review literature with respect to clinical features, genetics and management of this condition.

Materials and Methods:

A retrospective chart review was performed of three Omani patients who had been diagnosed with CFEOM in our institution. All patients had undergone standardized orthoptic and ocular evaluations and magnetic resonance imaging (MRI) of the orbits and brain.

Results:

The three patients (age range nine months - 10 years) presented a history of congenital strabismus. All patients had severe bilateral ptosis and mild to moderate visual impairment secondary to the ptosis and astigmatism. Two of three patients demonstrated a positive jaw-winking phenomenon. A moderate to large angle exotropia with varying amount of hypotropia and limitations of almost all the extra ocular muscles was noted. Patient 3 was also developmentally delayed. MRI brain and orbit showed abnormalities of the extraocular muscles in two patients and brain malformation in one patient.

Conclusions:

CFEOM is a rare, congenital, and non-progressive disorder with multiple extra ocular muscle restrictions. CFEOM can be associated with neuro-radiological abnormalities; its diagnosis and classification is defined by clinical characteristics and genetics. Options for treatment are limited and difficult.