A novel COL11A1 mutation affecting splicing in a patient with Stickler syndrome

Exon-Trapping Assay Improves Clinical Interpretation of COL11A1 and COL11A2 Intronic Variants in Stickler Syndrome Type 2 and Otospondylomegaepiphyseal Dysplasia

Stickler syndrome (SS) is a hereditary connective tissue disorder affecting bones, eyes, and hearing. Type 2 SS and the SS variant otospondylomegaepiphyseal dysplasia (OSMED) are caused by deleterious variants in COL11A1 and COL11A2, respectively. In both genes, available database information indicates a high rate of potentially deleterious intronic variants, but published evidence of their biological effect is usually insufficient for a definite clinical interpretation. We report four previously unpublished intronic variants in COL11A1 (c.2241 + 5G>T, c.2809 − 2A>G, c.3168 + 5G>C) and COL11A2 (c.4392 + 1G>A) identified in type 2 SS/OSMED individuals. The pathogenic effect of these variants was first predicted in silico and then investigated by an exon-trapping assay. We demonstrated that all variants can induce exon in-frame deletions, which lead to the synthesis of shorter collagen XI α1 or 2 chains. Lacking residues are located in the α-triple helical region, which has a crucial role in regulating collagen fibrillogenesis. In conclusion, this study suggests that these alternative COL11A1 and COL11A2 transcripts might result in aberrant triple helix collagen. Our approach may help to improve the diagnostic molecular pathway of COL11-related disorders.

Variable clinical expression of Stickler Syndrome: A case report of a novel COL11A1 mutation

Background

Stickler Syndrome is a rare connective tissue disorder, characterized by clinical, and genetic heterogeneity. The clinical expression is highly variable, including moderate to severe myopia in childhood, hearing loss, facial dysmorphic features, cleft palate, and early osteoarthritis. COL2A1, COL11A1, and COL11A2 mutations account of the majority of autosomal dominant Stickler Syndrome and, in particular, a heterozygous mutation in COL11A1 gene is identified in about 10 to 20% of Stickler Syndrome patients.

Methods

Herein, we report a case of an 8‐year‐ old child with Stickler Syndrome, presenting with early‐onset of myopia with vitreal abnormalities, facial dysmorphic characteristics, and mild hearing loss later in childhood. To identify the underlying genetic cause, Whole Exome Sequencing was carried out for COL11A1 gene.

Results

A novel de novo heterozygous splice site variant (NM_001854: c.1845 + 5G> C) of the COL11A1 gene, which had not been previously reported, was identified by Whole Exome Sequencing.

Conclusion

We reported a novel COL11A1 mutation in a child with Stickler Syndrome presenting a phenotype of early‐onset of ocular anomalies and mild hearing loss later in childhood. Our findings confirm the variability of the expression of the disease, even in the contest of the same gene‐related disorder, thus, contributing to improve the knowledge on clinical and molecular basis of this rare disease.

Phenotypic characterization of patients with early-onset high myopia due to mutations in COL2A1 or COL11A1: Why not Stickler syndrome?

PURPOSE

Our previous study reported that 5.5% of probands with early-onset high myopia (eoHM) had mutations in COL2A1 or COL11A1. Why were the probands initially considered to have eoHM but not Stickler syndrome (STL)?

METHODS

Probands and family members with eoHM and mutations in COL2A1 or COL11A1 were followed up and reexamined based on the criteria for STL. Further comprehensive examinations were conducted for patients with eoHM and mutations in COL2A1 or COL11A1 and controls with eoHM without mutations in COL2A1 or COL11A1. We performed comparisons between probands, affected family members with mutations in COL2A1 or COL11A1, and controls with eoHM without mutations in COL2A1 or COL11A1.

RESULTS

Twelve probands (8.91±4.03 years) and 14 affected family members (37.00±11.18 years) with eoHM and mutations in COL2A1 or COL11A1, as well as 30 controls with eoHM but without mutations in COL2A1 or COL11A1, were recruited. Among them, 25.0% of probands and 50.0% of affected family members met the diagnostic criteria for STL after reexamination. Posterior vitreous detachment/foveal hypoplasia (PVD/FH), hypermobility of the elbow joint (HJ), and vitreous opacity were more frequent in patients with eoHM with mutations in COL2A1 or COL11A1 than in the controls (p = 1.40 × 10^-5, 3.72 × 10^-4, 2.30× 10^-3, respectively). HJ was more common in the probands than in the affected family members (11/12 versus 3/14; p = 3.42 × 10^-4), suggesting age-dependent manifestation. EoHM presented in all the probands and in 11/14 affected family members, suggesting that it is a more common indicator of STL than the previously described vitreoretinal abnormalities, especially in children. The rate of STL diagnosis could increase from 25.0% to 66.7% for probands and from 50.0% to 92.9% for affected family members if eoHM, PVD/FH, and HJ are added to the diagnostic criteria.

CONCLUSIONS

In summary, it is not easy to differentiate STL from eoHM with routine ocular examination in outpatient clinics. Awareness of atypical phenotypes and newly recognized signs may be of help in identifying atypical STL, especially in children at eye clinics.

A novel dominant COL11A1 mutation in a child with Stickler syndrome type II is associated with recurrent fractures

This case describes a child with blindness, recurrent low-impact fractures, low bone mass, and intermittent joint pain who was found to have a novel missense mutation in COL11A1, consistent with Stickler syndrome type II. The case illustrates the phenotypic variability of the syndrome, which may include increased fragility in childhood.

INTRODUCTION

Stickler syndrome type II is an autosomal dominant disorder caused by mutations in the gene that encodes the type XI collagen chain α1 (COL11A1). Manifestations include craniofacial dysmorphology and ocular abnormalities that may lead to blindness, hearing loss, and skeletal anomalies that range from joint pain and arthritis to scoliosis and hypermobility.

METHODS

Herein, we describe a child who carried the presumed diagnosis of osteoporosis-pseudoglioma syndrome because of the combined findings of recurrent low-impact fractures due to low bone mass and blindness. The child also suffered from joint pain but had no facial dysmorphism or hearing loss.

RESULTS

Targeted sequencing and deletion analysis of the LRP5, COL1A1, and COL1A2 genes failed to identify any mutations, and whole exome sequence analysis revealed a novel missense mutation (c.3032C>A:p.P1011Q) in COL11A1, consistent with Stickler type II.

CONCLUSION

This case highlights the phenotypic variability of Stickler type II, broadens the list of differential diagnosis of increased bone fragility in childhood, and highlights utility of unbiased genetic testing towards establishing the correct diagnosis in children with frequent fractures.

A mild form of Stickler syndrome type II caused by mosaicism of COL11A1

Stickler syndrome, a clinically as well as molecularly heterogeneous connective tissue disorder, is predominantly inherited in an autosomal dominant manner and is considered complete penetrant. Previously, mosaicism in Stickler syndrome has been reported in only a few cases. We describe a child with Stickler syndrome due to a novel splice site mutation in COL11A1. Initially, Sanger sequencing of both parents showed normal test results for the mutation. Due to mild phenotypic traits, the father was tested again using a more sensitive method (NGS), and was found to have low-grade mosaicism in various tissue samples (range 7-22% of the DNA). Therefore, we recommend using sensitive genetic testing when mosaicism is suspected. Furthermore, we support previous suggestions of parental testing even when the parents of an affected patient do not have obvious phenotypic signs of Stickler syndrome.

A novel COL11A1 missense mutation in siblings with non-ocular Stickler syndrome

Stickler syndrome (STL) is an autosomal, dominantly inherited, clinically variable and genetically heterogeneous connective tissue disorder characterized by ocular, auditory, orofacial and skeletal abnormalities. We conducted targeted resequencing using a next-generation sequencer for molecular diagnosis of a 2-year-old girl who was clinically suspected of having STL with Pierre Robin sequence. We detected a novel heterozygous missense mutation, NM_001854.3:n.4838G>A [NM_001854.3 (COL11A1_v001):c.4520G>A], in COL11A1, resulting in a Gly to Asp substitution at position 1507 [NM_001854.3(COL11A1_i001)] within one of the collagen-like domains of the triple helical region. The same mutation was detected in her 4-year-old brother with cleft palate and high-frequency sensorineural hearing loss.