Exome sequencing of the proband's affected daughter uncovered a heterozygous <i>CRX</i> deletion [NM_000554.4: CRX: c.(100 + 1_101-1)_(c.900 + 1_?)del] that segregated with the disease.<b>Conclusion</b>: An unusual familial cone-rod dystrophy phenotype was associated with heterozygous <i>CRX</i> deletion, a pathogenic variant that had a presumed mechanism of haploinsufficiency.
To characterize by multimodal approach the phenotype of patients from a 3 generations pedigree, affected by autosomal dominant cone-rod dystrophy (CRD), found to carry a novel pathogenic variant in the cone-rod homeobox-containing (CRX) gene.
Patients with pattern dystrophy (PD) were screened for mutations in PRPH2, BEST1, ELOVL4, CTRP5, and ABCA4; patients with cone-rod dystrophy (CRD) were screened for mutations in CRX, ABCA4, PRPH2, ELOVL4, and the c.2513G>A p.Arg838His variant in GUCY2D.
Mutations in the human CRX gene are associated with dominant inherited retinopathies Retinitis Pigmentosa (RP), Cone-Rod Dystrophy (CoRD), and Leber Congenital Amaurosis (LCA), of varying severity.
Mutations in the cone-rod homeobox gene (CRX) are associated with cone-rod dystrophy (CORD), Leber congenital amaurosis (LCA), and, in rare cases, retinitis pigmentosa (RP).
This is in accordance with the theory that ataxin-7 interacts with CRX transcription, since it is known that mutations in the CRX gene cause cone-rod dystrophy.
A novel heterozygous complex mutation (c.816delCACinsAA) in CRX predicting the substitution of 27 C-terminal amino acids by 44 novel amino acids, thus abolishing the OTX tail, was identified in a 2-generation family finally diagnosed with cone-rod dystrophy (CRD), which was confirmed by 2CTP.
The four major causative genes involved in the pathogenesis of CRDs are ABCA4 (which causes Stargardt disease and also 30 to 60% of autosomal recessive CRDs), CRX and GUCY2D (which are responsible for many reported cases of autosomal dominant CRDs), and RPGR (which causes about 2/3 of X-linked RP and also an undetermined percentage of X-linked CRDs).
As an example, we discover an unannotated Tf_Otx Pfam domain on the cone rod homeobox protein, which suggests a possible mechanism for how the V242M mutation on this protein causes cone-rod dystrophy.
ERG and molecular genetic findings were consistent with the reclassification of this disease as an autosomal dominant cone-rod dystrophy (CRD) CONCLUSIONS: We report a novel CRX mutation causing autosomal dominant CRD.
Mutations in CRX, a photoreceptor-specific transcription factor, can cause Leber congenital amaurosis (LCA), cone-rod dystrophy (CORD), and retinitis pigmentosa (RP), all of which feature severe visual impairment.
The Ala196+1bp mutation was associated with an early-onset, severe form of cone-rod dystrophy similar to that described in the original CORD2 family (Evans et al., Arch Ophthalmol 1995;113:195-201).
Two point mutations of Crx, R41W and E80A, that cause cone-rod dystrophy in humans and lie within the homeodomain but outside the NLS did not disrupt the nuclear localization of Crx protein, but a R90W mutation of Crx that causes human Leber congenital amaurosis (LCA) and resides within the NLS resulted in the fusion protein localized in both nuclei and cytoplasm in majority (51% to 69%) of the transfected cells.