ClinVar Genomic variation as it relates to human health

In affected members of 5 families diagnosed with malattia leventinese (MLVT), also known as Doyne honeycomb retinal dystrophy (DHRD; 126600), including 2 families from the U.S., 2 from Switzerland, and 1 from Australia, Stone et al. (1999) identified heterozygosity for a C-T transition in the EFEMP1 gene, resulting in an arg345-to-trp (R345W) substitution. They then assessed the potential involvement of this variation in MLVT, DHRD, and age-related macular dystrophy (ARMD; see 153800) by SSCP screening of all 162 affected patients in 37 families, as well as 477 control individuals and 494 unrelated patients with ARMD. They found that DNA from 161 of 162 patients initially thought to be affected with MLVT or DHRD harbored an SSCP shift in exon 10 resulting from the R345W mutation. This shift was found in none of the DNA from ARMD or control individuals. Of the 161 MLVT/DHRD patients harboring the R345W mutation, 160 were heterozygotes; 1 individual was homozygous for this change and had a retinal phenotype equivalent to that of heterozygotes of similar age. Stone et al. (1999) reexamined the retinal photographs of the 2 'affected' members of the single family that was discordant for the R345W change and found that the individual with the mutation had the characteristic MLVT phenotype (and the shared Swiss haplotype), whereas the individual lacking the mutation had a phenotype more typical of common ARMD (and failed to share alleles with the Swiss haplotype). This is, then, an exceptionally close genotype/phenotype correlation. Stone et al. (1999) also investigated samples from 2 nuclear families with genealogic evidence for a relationship with the original DHRD family reported by Doyne (1899), and found that affected individuals from both families harbored the R345W variation. Noting the absence of de novo R345W mutations in the 39 families they studied, and the complete sharing of alleles of 4 intragenic EFEMP1 polymorphisms among these families, Stone et al. (1999) suggested that the R345W mutation occurred only once, in a common ancestor of every affected patient in the study. Tarttelin et al. (2001) identified this mutation in 7 of 10 families with Doyne honeycomb retinal dystrophy and 1 of 17 sporadic patients. In a consanguineous Indian family with early-onset macular degeneration, Fu et al. (2007) identified the R345W mutation in the EFEMP1 gene. The mother and father were heterozygous for the mutation, whereas their more severely affected sons were homozygous. The disease haplotype in this family was distinctly different from previously reported haplotypes, suggesting that the mutation arose independently. In a Chinese family in which a sister and brother and their mother had DHRD/MLVT, Zhang et al. (2018) sequenced the EFEMP1 gene and identified heterozygosity for the recurrent R345W mutation. In a 32-year-old Swiss woman with MLVT, Vaclavik et al. (2020) identified heterozygosity for a de novo occurrence of the recurrent R345W mutation (c.1033C-T, NM_001039349.2). In a 57-year-old Danish woman with DHRD, Sheyanth et al. (2021) sequenced 7 genes associated with flecked retina and identified heterozygosity for the R345W mutation in EFEMP1. No pathogenic variants were found in the remaining genes. Analysis of microsatellite markers and intragenic SNPs indicated a different haplotype compared to the original study by Stone et al. (1999), suggesting that the mutation arose independently. Variant Function Hulleman et al. (2011) noted that arg345 is adjacent to cys344, which is required to form the second disulfide bond of EGF domain-6 in EFEMP1. By examining secretion of mutant EFEMP1 proteins in transfected HEK293T cells, they found that the R345W mutation or substitution of R345 with a different aromatic residue interfered with disulfide bond formation and secretion of EFEMP1. EFEMP1 with the R345W mutation accumulated intracellularly. Using immunocytochemistry to analyze transfected COS-7 cells, Collantes et al. (2022) observed increased intracellular retention of the R345W mutant compared to wildtype EFEMP1, which was confirmed by Western blot analysis. Tsai et al. (2021) found that genetic correction of the EFEMP1 R345W mutation in induced pluripotent stem cells (iPSCs) from individuals with DHRD alleviated reduced EFEMP1 secretion but did not affect iPSC differentiation into retinal pigment epithelium cells (iRPEs). Proteomic profiling revealed a significant number of differentially expressed genes between iRPE cells derived from iPSCs of DHRD-affected individuals and wildtype iRPE cells; however, correction of the R345W mutation greatly reduced the number of differentially expressed genes. ELISA showed that, in contrast to previous reports, EFEMP1 R345W iRPEs did not display inflammatory cytokine release or unfolded protein response. Instead, they exhibited downregulation of CES1 (114835), an enzyme expressed predominantly in the RPE layer of human eye that converts cholesteryl ester to free cholesterol. The reduced CES1 expression hampered secretion of cholesterol, leading to lipid accumulation in iRPEs. Further analysis showed that the EFEMP1 R345W mutant had a hyperinhibitory effect on EGFR (131550) signaling, resulting in downregulation of the transcription factor SP1 (189906), which controlled CES1 transcription by binding to its promoter. (less)