Frail inner limiting membrane maculopathy suggested to describe a new retinal Alport-like condition with two variants in three generations of females

We report a three-generation family with isolated Alport-like retinal abnormalities in the absence of lenticonus, hearing loss, kidney disease, and detectable molecular genetic defects in known Alport-related genes. Clinical examination includes ocular biomicroscopy, fundus photography, optical coherence tomography, dipstick urinalysis, serum creatinine assessment, and molecular genetic analysis. The proband, her mother, and her maternal grandmother had normal best-corrected visual acuity and normal visual fields in both eyes. The macula presented a petaloid stair-case profile with scarce vessels in both eyes of the proband and a flat temporal macula lacking a foveal avascular zone in her mother and her grandmother. No family member had renal symptoms, unexplained subnormal hearing, or lenticonus. Sequencing and MLPA found no defect in COL4A3, COL4A4, and COL4A5. Common SNPs around the genes ± 1Mb showed no segregation. Furthermore, none of the variants shared between the affected individuals in genes from a gene panel of genes relevant for ophthalmopathy nor whole exome- and genome sequencing explained the phenotype. A new condition with two retinal Alport-like phenotypes was found. No abnormalities of the kidneys and lens were found, neither abnormalities of the type IV collagen genes related to Alport syndrome. Homology with retinal abnormalities seen in patients after surgical removal of the inner limiting membrane of the retina suggests that this is where the defect is located. We therefore suggest that the new retinal phenotypes and similar phenotypes can be described with the new definition “frail inner limiting membrane maculopathy.”</p

Common Founder mutations in the <i>COL4A5</i>, <i>COL4A3</i> and <i>COL4A4</i> genes.

<p>Common Founder mutations in the <i>COL4A5</i>, <i>COL4A3</i> and <i>COL4A4</i> genes.</p

Age at end-stage renal failure and severity of mutations with <i>COL4A5</i>, <i>COL4A3</i> and <i>COL4A4</i> variants.

<p>Age at end-stage renal failure and severity of mutations with <i>COL4A5</i>, <i>COL4A3</i> and <i>COL4A4</i> variants.</p

Observed versus expected likelihood of Glycine substitutions in the <i>COL4A5</i>, <i>COL4A3</i> and <i>COL4A4</i> genes in Alport syndrome and Thin basement membrane nephropathy.

<p>Observed number from the LOVD databases; expected number derived from data for collagen I [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0161802#pone.0161802.ref020" target="_blank">20</a>].</p

Distribution of missense variants in the <i>COL4A5</i> gene in each exon corrected for exon size and demonstrating a non-uniform distribution.

<p>Distribution of missense variants in the <i>COL4A5</i> gene in each exon corrected for exon size and demonstrating a non-uniform distribution.</p

Details of the clinical diagnoses and genetic pathology identified in individuals in this study.

<p>Details of the clinical diagnoses and genetic pathology identified in individuals in this study.</p

Identification of regulatory deletions telomeric to <i>PAX6</i>.

<p>Regulatory deletions telomeric to <i>PAX6</i> were identified in individual 1514 (chr11:30,874,642–31,654,833), individual 753 (chr11:30,967,000–31,704,000), individual 555 (chr11:31,108,579–31,649–842), individual 2014 (chr11:31,234,395–31,751,815) and individual 659 (chr11:31,379,000–31,708,000). The schematic diagram shows how the ‘critical region’ (delimited by grey dotted lines) required for <i>PAX6</i> transcriptional activation was delineated by combining our data with published deletions with known coordinates [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0153757#pone.0153757.ref055" target="_blank">55</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0153757#pone.0153757.ref067" target="_blank">67</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0153757#pone.0153757.ref068" target="_blank">68</a>]. <i>PAX6</i> regulatory deletions from the present study are shown by red blocks. Genes transcribed on the forward strand are in blue and those transcribed on the reverse strand are in green, also indicated by arrows. Genomic coordinates are based on the Human Genome Assembly hg18.</p

Identification of a potential <i>PITX2</i> regulatory deletion.

<p>Genome-wide array CGH identified a deletion of approximately 3.5 Mb in individual 1194 (chr4:111,994,000–115,504,000) (red bar). The deletion is located telomeric to the <i>PITX2</i> gene on chromosome 4. The positions of conserved elements (CE) in the deleted region, as identified by Volkmann et al., 2011 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0153757#pone.0153757.ref047" target="_blank">47</a>] are marked by orange ellipses. Genes transcribed on the forward strand are in blue and those transcribed on the reverse strand are in green, also indicated by arrows. Genomic coordinates are shown on the x-axis and are based on the Human Genome Assembly hg18.</p

Mutation analysis of the <i>FOXC1</i> locus.

<p><b>(A)</b> Genome-wide array CGH identified two deletions encompassing the <i>FOXC1</i> gene in individuals 1449 (chr6:1,543,591–1,675,085) and 1246 (chr6:1,543,591–1,675,085). <b>(B)</b> Direct sequencing of the <i>FOXC1</i> coding region identified a heterozygous substitution in individual 1839 (c.235C>A, p.(Pro79Thr)) and another in individual 1634 (c.302T>C, p.(Leu101Pro)). <i>FOXC1</i> mutation screening in unaffected parents of both patients showed that the mutations had occurred <i>de novo</i>. The locations of both mutations within the fork-head domain of the FOXC1 protein are indicated by vertical arrows. Genes transcribed on the forward strand are in blue and those transcribed on the reverse strand are in green, also indicated by arrows. Genomic coordinates are based on the Human Genome Assembly hg18. The genomic sequence identifier for <i>FOXC1</i> is NG_009368.</p

Identification of <i>PAX6</i> whole-gene deletions.

<p>Genome-wide array CGH analysis identified a 650 kb deletion in individual 2193 (chr11:31,199,000–31,849,000), a 520 kb deletion in individual 377 (chr11:31,394,000–31,914,000), a 154 kb deletion in individual 1510 (chr11:31,779,000–31,933,000) and a 96 kb deletion in individual 1977 (chr11:31,698,271–31,794,414), all involving <i>PAX6</i>. Red bars show the position of the deletions. Genes transcribed on the forward strand are in blue and those transcribed on the reverse strand are in green, also indicated by arrows. Genomic coordinates are based on the Human Genome Assembly hg18.</p