Molecular genetics of Stickler and Marshall syndromes, and the role of collagen II and other candidate proteins in high myopia and impaired hearing

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>Stickler and Marshall syndromes are genetic disorders both inherited in an autosomal dominant manner. The genotype-phenotype correlation was performed in ten Stickler/Marshall syndrome patients with mutations in the <em>COL11A1</em> gene. Four patients had a phenotype classified as Marshall syndrome based on early-onset severe hearing loss and characteristic facial dysmorphism. A splice site mutation in intron 50 of <em>COL11A1</em> was found in these patients, while the remaining six patients had an overlapping Marshall-Stickler phenotype with a mutation elsewhere in the gene. These results indicate exon 50 as a hot spot for splice site mutations leading to a phenotype of Marshall syndrome rather than Stickler syndrome. </p><p>Collagen II (<em>COL2A1</em>) precursor mRNA undergoes alternative splicing resulting in two different isoforms, IIA including exon 2 and IIB excluding exon 2. Recent evidence indicates that premature termination codon mutations in exon 2 cause Stickler syndrome with no or minimal extraocular manifestations. </p><p>Two mutations were observed in this study: Cys64Stop, and a novel structural mutation, Cys57Tyr. Results from the <em>COL2A1</em> mini-gene studies suggested that both mutations altered positive <em>cis</em> elements for splicing resulting in a lower IIA:IIB ratio. The results further emphasize the importance of exon 2 in the development and normal function of the eye. In addition, patients displaying eye phenotypes in the absence of extraocular manifestations should be analyzed first for exon 2 mutations.</p><p>Linkage analysis identified a new locus for autosomal recessive nonsyndromic hearing loss (DFNB32) on chromosome 1p13.3-22.1 in a Tunisian family with congenital profound autosomal recessive deafness. The <em>COL11A1</em> gene is located in this region and was analyzed as a candidate gene. No disease causing sequence variation was observed. </p><p>The analysis of 85 English and 40 Finnish subjects with high myopia resulted in the identification 23 sequence variations in the SLRP genes <em>LUM</em>, <em>FMOD</em>, <em>PRELP</em>, and <em>OPTC</em>. The two intronic variations and seven amino acid changes, one synonymous and six non-synonymous, were not found in the 308 controls analyzed. Five changes were detected in opticin, and all but one were shown to co-segregate with high myopia in families with incomplete penetrance. The results suggested that sequence variations in the SLRP genes expressed in the eye are genetic risk factors underlying the pathogenesis of high myopia. </p></div>