Duane syndrome in the setting of chromosomal duplications

Duane syndrome in association with congenital disorder of glycosylation type Ig (ALG12-CDG)

Congenital disorders of glycosylation type I (CDG-I) are a group of autosomal recessive genetic multisystem disorders that arise from defective glycoprotein biosynthesis. Although ocular abnormalities have been described in patients with CDG-I, few ocular abnormalities have been associated with ALG12-CDG (CDG-Ig), a rare subtype of CDG-I. We report a case of Duane syndrome, a congenital strabismus syndrome, in a 17-year-old young woman with ALG12-CDG.

Recurrent Rare Copy Number Variants Increase Risk for Esotropia

Purpose

To determine whether rare copy number variants (CNVs) increase risk for comitant esotropia.

Methods

CNVs were identified in 1614 Caucasian individuals with comitant esotropia and 3922 Caucasian controls from Illumina SNP genotyping using two Hidden Markov model (HMM) algorithms, PennCNV and QuantiSNP, which call CNVs based on logR ratio and B allele frequency. Deletions and duplications greater than 10 kb were included. Common CNVs were excluded. Association testing was performed with 1 million permutations in PLINK. Significant CNVs were confirmed with digital droplet polymerase chain reaction (ddPCR). Whole genome sequencing was performed to determine insertion location and breakpoints.

Results

Esotropia patients have similar rates and proportions of CNVs compared with controls but greater total length and average size of both deletions and duplications. Three recurrent rare duplications significantly (P = 1 × 10⁻⁶) increase the risk of esotropia: chromosome 2p11.2 (hg19, 2:87428677-87965359), spanning one long noncoding RNA (lncRNA) and two microRNAs (OR 14.16; 95% confidence interval [CI] 5.4–38.1); chromosome 4p15.2 (hg19, 4:25554332-25577184), spanning one lncRNA (OR 11.1; 95% CI 4.6–25.2); chromosome 10q11.22 (hg19, 10:47049547-47703870) spanning seven protein-coding genes, one lncRNA, and four pseudogenes (OR 8.96; 95% CI 5.4–14.9). Overall, 114 cases (7%) and only 28 controls (0.7%) had one of the three rare duplications. No case nor control had more than one of these three duplications.

Conclusions

Rare CNVs are a source of genetic variation that contribute to the genetic risk for comitant esotropia, which is likely polygenic. Future research into the functional consequences of these recurrent duplications may shed light on the pathophysiology of esotropia.

Chromosomal microarray analysis of patients with Duane retraction syndrome

PURPOSE

Duane retraction syndrome (DS) is a rare congenital strabismus with genetic heterogeneity. The genetic causes of DS are not always of monogenic origin; various chromosomal copy number variations (CNVs) have also been reported. The objective of our study was to characterize the CNVs, including gains and losses detected by high-resolution chromosomal microarray in patients with DS.

METHODS

Twenty patients with DS were investigated using high-resolution chromosomal microarray analysis (CMA) (Affymetrix CytoScan Array 750 K). Conventional cytogenetic analysis was also performed.

RESULTS

All samples revealed normal karyotype by cytogenetic analysis. However, in all our patients, multiple CNVs, including gains and losses, were detected using the high-resolution CMA method. Chromosomal loci 1q21.2, 2p11.2-q11.1, 2q21.1-q21.2, 4p16.1, 7p11.2-q11.21, 14q32.33, 17p11.2-q11.1 and 20p11.1-q11.21 were the most frequently affected regions.

CONCLUSIONS

This study emphasized that CNVs in several chromosomal regions are known to be involved in DS. We also underscore the genetic heterogeneity of DS. Our suggestion is that genes located in the most frequently affected regions should be focused on in the following candidate gene studies.

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 genetics of nonsyndromic bilateral Duane retraction syndrome

PURPOSE

To assess the importance of monogenic mutations and chromosomal copy number variants (CNVs) in the occurrence of nonsyndromic bilateral Duane retraction syndrome (bilateral nsDRS).

METHODS

The medical records of 12 patients with bilateral nsDRS were reviewed. Genes associated with DRS and associated congenital cranial dysinnervation disorders (SALL4, CHN1, HOXA1, TUBB3, and KIF21A) were sequenced in the standard fashion in each patient. Array comparative genomic hybridization (array CGH) was performed using Affymetrix Cytogenetics Whole-Genome 2.7M array, and the results were analyzed using Affymetrix Chromosome Analysis Suite v1.2. CNVs were assessed as unlikely to be pathologic if they were also present in the Database of Genomic Variants (DGV) or our local database of array CGH results in 150 normal individuals of Middle Eastern ethnicity.

RESULTS

No patient had a sequence mutation in SALL4, CHN1, HOXA1, TUBB3, or KIF21A. These 12 patients each had 36-42 chromosomal deletions and/or duplications (mean with standard deviation, 26.25 ± 6.77), but all of these CNVs were present either in the DGV or in our local database of normal individuals of similar ethnicity and, therefore, are considered nonpathogenic.

CONCLUSIONS

The results reported here suggest that bilateral nsDRS is not usually associated with mutations in these genes or with chromosomal CNVs. Current evidence suggests other factors such as epigenetic and/or teratogenic abnormalities may be a potential cause of bilateral nsDRS.

Duane retraction syndrome in a patient with Duchenne muscular dystrophy

PURPOSE

We describe the clinical features of a boy with bilateral Duane retraction syndrome (DRS), Duchenne muscular dystrophy (DMD), and other medical problems.

METHODS

The child was followed-up for five years; his chart was reviewed, including the results of a muscle biopsy and genetic testing. Multiplex ligation-dependent probe amplification (MLPA) was used to interrogate deletions/duplications in the dystrophin gene.

RESULTS

The proband had bilateral DRS with otherwise normal ocular motility; he also had developmental delay, mild mental retardation, and seizures. Clinical diagnosis of DMD included progressive proximal weakness, highly elevated creatine kinase levels, and a muscle biopsy showing significant dystrophic changes including contracted, degenerative, and regenerative fibers, and negative dystrophin immunostaining. MLPA documented duplication of exons 3 and 4 of the dystrophin gene.

CONCLUSIONS

This boy is the third patient to be reported with DRS and DMD, the second with bilateral DRS and the only one with other neurologic features. Mutated dystrophin is present in extraocular muscles and in the central nervous system (CNS) in DMD, leaving open the question of whether this co-occurrence is the result of the genetic muscle abnormality, CNS effects caused by dystrophin mutations, or chance.

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).

CCDD Phenotype Associated with a Small Chromosome 2 Deletion

PURPOSE

Some individuals are born with congenital limitation of ocular motility, often associated with ptosis and retraction of the globe. Many of these disorders are now known as the congenital cranial dysinnervation disorders (CCDDs). While several genes have been associated with CCDD phenotypes, there are still patients for whom the genetic basis has not been identified.

METHODS

Clinical evaluation and neuroimaging, sequencing of candidate genes, and array comparative genomic hybridization (array CGH).

RESULTS

The patient was a four-year-old girl with mild dysmorphism; bilateral mild ptosis; substantial limitation of abduction OS with milder limitations of abduction OD, adduction OS, and vertical gaze OS; and retraction OS > OD on attempted adduction. No mutations were detected in the HOXA1, KIF21A, SALL4, TUBB3, and CHN1 genes. Array CGH revealed a 8 Kb de novo deletion on chromosome 2 (2q24.3) that encompassed a portion of only one gene, the Xin Actin-binding Repeat containing 2 (Gene Symbol XIRP2; NM_001079810). This gene encodes a protein that is involved in muscle development and protecting actin filaments from depolymerization. It interacts functionally with 10 other proteins playing a similar role in muscle development.

CONCLUSIONS

This patient's chromosomal abnormality affected only one gene that currently seems involved only in muscle development. All other genes currently associated with the CCDDs affect neurologic development. Genetic information from this patient implies that genes involved in development and maintenance of extraocular muscles can cause congenital ocular motility disorders as well.

Partial duplication of chromosome 19 associated with syndromic duane retraction syndrome

BACKGROUND

To evaluate possible monogenic and chromosomal anomalies in a patient with unilateral Duane retraction syndrome, modest dysmorphism, cerebral white matter abnormalities, and normal cognitive function.

MATERIALS AND METHODS

Performing high-resolution array comparative genomic hybridization (array CGH) and sequencing of HOXA1, KIF21A, SALL4, and CHN1 genes.

RESULTS

The proband had unilateral Duane retraction syndrome (DRS) type III on the right with low-set ears, prominent forehead, clinodactyly, and a history of frequent infections during early childhood. Motor development and cognitive function were normal. Parents were not related, and no other family member was similarly affected. MRI revealed multiple small areas of high signal on T2 weighted images in cerebral white matter oriented along white matter tracts. Sequencing of HOXA1, KIF21A, SALL4, and CHN1 did not reveal any mutation(s). Array CGH showed a 95 Kb de novo duplication on chromosome 19q13.4 encompassing four killer cell immunoglobulin-like receptor (KIR) genes. Conclusions. KIR genes have not previously been linked to a developmental syndrome, although they are known to be expressed in the human brain and brainstem and to be associated with certain infections and autoimmune diseases, including some affecting the nervous system. DRS and brain neuroimaging abnormalities may imply a central and peripheral oligodendrocyte abnormality related in some fashion to an immunomodulatory disturbance.

Duane syndrome in association with 48,XXYY karyotype

Duane syndrome is an ocular motility disorder consisting of deficient horizontal eye movements, eyelid retraction, palpebral fissure narrowing, and abnormal vertical eye movements. It occurs in 1%-5% of patients with strabismus and has also been reported in several syndromes and chromosome abnormalities. Although most cases are sporadic, autosomal-dominant inheritance is seen in up to 10% of cases. Recently, Duane syndrome has been reported to occur in the setting of chromosomal duplication. The 48,XXYY syndrome is a rare syndrome involving duplication of the sex chromosomes. Ocular abnormalities are not typical of this condition. We report the first case of Duane syndrome presenting in an 8-month-old boy with XXYY syndrome. This case lends further support to the association of chromosomal duplication and Duane syndrome.