Single-base substitutions in theCHMpromoter as a cause of choroideremia

Abstract

45Although over 150 unique mutations affecting the coding sequence of CHM have been identified 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 peripheral vision (Karna, 1986;Roberts et al., 2002). 76To date, CHM has only been linked to mutations within the CHM gene, coding for REP-1 77 (Cremers et al., 1990). The protein serves as a molecular chaperone for small GTPases from the Rab proteins is essential for intracellular vesicular transport (Seabra et al., 1992; Seabra et al., 81 1993). A homologue, REP-2, encoded by CHML or choroideremia-like, functions similarly and 82 appears to compensate for the absence of REP-1 in all tissues except the eye (Cremers et al., 83 1994). CHM spans over 150 kb of Xq21.2 and contains 15 exons (van Bokhoven et al., 1994). A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Missense mutations predicted to alter protein structure or impair function (Sergeev et al., 2009; 91 Esposito et al., 2011), transposon insertions (Van Den Hurk et al., 2003), partial gene 92 duplications (Chi et al., 2013;Simunovic et al., 2016) and other variations are infrequently 93 found, but taken collectively, almost all known pathogenic variants in the CHM gene have been 94 loss of function mutations that abolish functional REP-1 (McTaggart et al., 2002; Simunovic et 95 al., 2016). Notably there is no apparent correlation between genotype and phenotype, with the 96 age at onset of symptoms, visual acuity and visual fields being unrelated to mutation type 97 (Freund et al., 2016;Simunovic et al., 2016). 98The promoter driving expression of CHM has been heretofore unidentified. Analyses of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Materials and Methods 128 Clinical Examination and Study Subjects 129This study was approved by the institutions' respective ethics review boards. All procedures 130 adhered to the tenets of the Declaration of Helsinki. Before participation, the purpose and risks 131 of the study were explained, and informed consent was obtained. Blood samples were drawn, 132 and a detailed pedigree and history was recorded. 133We studied 4 males affected by CHM and 1 carrier female from two unrelated families. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 (Anderson and Gusella, 1984). Cells were 157 maintained in RPMI-1640 supplemented with 15% fetal ...

Findings from a Genotyping Study of over 1000 People with Inherited Retinal Disorders in Ireland

“…Recent studies have highlighted that molecular diagnostic yield is increased when WGS is employed by comparison with other methods [51]. It is expected that for many of the currently unresolved cases, pathogenic variants may be present in deep-intronic, promoter, enhancer regions or in genes that are not yet associated with an IRD [73,74]. Recent studies such as that in STGD1, highlighting the relative prevalence of deep intronic mutations in the ABCA4 gene, attest to the need for more extensive sequence analysis [13].…”

Toward an elucidation of the molecular genetics of inherited retinal degenerations

“…In addition to CNVs and splice variants as a source of as yet ‘unresolved’ pathogenic IRD mutations, variants in regulatory sequences, such as, promoter sequences or miRNAs, and their associated target sites, may also be implicated in some forms of IRD. Indeed a mutation in the seed region of microRNA-204 has been found to segregate in a family with autosomal dominantly inherited retinal dystrophy and bilateral coloboma ( 44 ), a 5’UTR sequence in the NMNAT1 gene has been implicated in a form of LCA ( 45 ) and recently a single base mutation in the promoter region of the CHM gene has been implicated as causative of choroideremia ( 46 ), all highlighting the potential role of regulatory mutations in some forms of IRD. The implementation of more extensive NGS strategies in the future will aid in characterising such IRD regulatory mutations.…”

Crystals and Fatty Acid Abnormalities Are Not Present in Circulating Cells From Choroideremia Patients

“…8 The ubiquitous expression profile of REP-1 and the essential role of Rab prenylation could suggest that CHM may also result in systemic abnormalities. 9,10 While certain Rabs have indeed been associated with syndromic diseases such as Griscelli syndrome type 2 (Rab27) and Charcot-Marie-Tooth disease type 2B (Rab7), 11,12 CHM has been viewed as a retinal disease, with no significant nonocular symptoms reported in males or carrier females. Previous work has demonstrated that a loss of REP-1 in fibroblasts and monocytes affected intracellular transport, increased pH levels in lysosomes, impaired proteolytic degradation, and altered secretion of cytokines, but these effects did not appear to translate to wider systemic effects.…”