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Novel Mutation in the COL11A1 Gene Causing Marshall-Stickler Syndrome in Three Generations of a Bulgarian Family.

ABSTRACT: Here we report the first familial case spread through at least three generations, genetically verified cases of Marshall-Stickler syndrome in Bulgaria. The proband, a 2-year-old girl, has craniofacial dysplasia, ocular hypertelorism, small saddle nose with a flat bridge and midface hypoplasia. The pedigree of the proband's family showed that her father has the same clinical manifestations of the disease. In addition, her father presented with a tall, thin stature and mild hearing loss, manifested with aging. The same dysmorphological symptoms were presented by the paternal grandfather. Both patients, the 2-year-old girl and her father, have been diagnosed to carry Marshall-Stickler syndrome. The COL2A1 gene tested negative in the family. Based on the higher percentage of mutations in the COL2A1 gene, we analyzed this gene as the first target in the family. The COL2A1 gene tested negative, and we sequenced the gene further. A novel splice site mutation c.3474+1G>A was found in intron 44. This variant is related to the clinical presentation in the patient and her father. The c.3474+1G>A mutation results in altered splicing affects at the donor splice site of intron 44, which most probably gives a nonfunctional protein. The variant affects the major triple-helical domain that represents a mutation hot-spot for the gene.

SUBMITTER: Mladenova M

PROVIDER: S-EPMC8366474 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:Type 2 Stickler syndrome is usually a dominant disorder resulting from pathogenic variants in COL11A1 encoding the alpha 1 chain of type XI collagen. Typical molecular changes result in either substitution of an obligate glycine within the Gly-Xaa-Yaa amino acid sequence repeat region of the molecule, mRNA missplicing or deletions/duplications that typically leaves the message in-frame. Clinical features include myopia, retinal detachment, craniofacial, joint, and hearing problems. Fibrochondrogenesis is also a COL11A1 related disorder, but here disease-associated variants are recessive and may be either null alleles or substitutions of glycine, and the condition is usually lethal in infancy. METHODS:The patient was assessed in the NHS England Stickler syndrome diagnostic service. DNA from the patient and family were analyzed with Next Generation Sequencing on a panel of genes known to cause Stickler Syndrome. The effect of sequence variants was assessed using minigene analysis. Allele-specific RT-PCR was performed. RESULTS:This patient had clinical type 2 Stickler syndrome but with severe hearing loss and severe ocular features including retinal atrophy and retinal tears in childhood. We identified a de novo in frame deletion of COL11A1 (c.4109_4126del) consistent with dominantly inherited Stickler syndrome but also a second inherited variant (c.1245+2T>C), on the other allele, affecting normal splicing of COL11A1 exon 9. CONCLUSION:Exon 9 of COL11A1 is alternatively expressed and disease causing changes affecting only this exon modify the phenotype resulting from biallelic COL11A1 disease-associated variants and, instead of fibrochondrogenesis, produce a form of Stickler syndrome with severe hearing loss. Disease phenotypes from de novo pathogenic variants can be modified by inherited recessive variants on the other allele. This highlights the need for functional and family analysis to confirm the mode of inheritance in COL11A1-related disorders, particularly for those variants that may alter normal pre-mRNA splicing.

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Novel Mutation in the COL11A1 Gene Causing Marshall-Stickler Syndrome in Three Generations of a Bulgarian Family.

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