Identification of a novel p.R1443W mutation in RP1 gene associated with retinitis pigmentosa sine pigmento

AIM:To screen mutations in the retinitis pigmentosa 1(RP1) gene and the rhodopsin(RHO) gene in Chinese patients with retinitis pigmentosa sine pigmento(RPSP)and describe the genotype-phenotype relationship of the mutations.·METHODS:Twenty affected,unrelated Chinese individuals with RPSP(4 autosomal dominant RPSP,12autosomal recessive RPSP and 4 unknown inheritance pattern) were recruited between 2009 and 2012.The clinical features were determined by complete ophthalmologic examinations.Polymerase chain reaction(PCR) and direct DNA sequencing were used to screen the entire coding region and splice junctions of the RP1gene and the RHO gene.The cosegregation analysis and population frequency studies were performed for patients with identified mutations.·RESULTS:Five variants in the RP1 gene and one in the RHO gene were detected in 20 probands.Four missense changes(rs444772,rs446227,rs414352,rs441800) and one non-coding variant(rs56340615) were common SNPs and none of them showed a significant relationship with RPSP.A missense mutation p.R1443W was identified in the RP1 gene in three affected individuals from a family with autosomal dominant RPSP and was found to cosegregate with the phenotype in this family,suggestive of pathogenic.In addition,population frequency analysis showed the p.R1443W mutation was absent in 300 healthy controls.·CONCLUSION:The identification of p.R1443W mutationcosegregating in a family with autosomal dominant RPSP highlights an atypical phenotype of the RP1 gene mutation,while RHO gene is not associated with the pathogenesis of RPSP in this study.To our knowledge,this is the fist mutation identified to associate with RPSP.

SCREENING FOR MUTATIONS IN A NOVEL RETINAL - SPECIFIC GENE AMONG CHINESE PATIENTS WITH RETINITIS PIGMENTOSA

Objective. To identify and evaluate mutations in the RPl gene among Chinese patients with retinitis pigmen-tosa (RP).Methods. Leukocyte DNA of 92 RP patients were collected in Hong Kong. Sequence changes of the entire coding region of the RP1 gene were examined using PCR, conformation sensitive gel electrophoresis and DNA sequencing.Results. In total, 1 nonsense mutation and 1 nonsense variant as well as 10 missense alterations were identified in the RP1 gene, among which, Arg677Ter was found in 1 RP patient and another nonsense variant, Argl933Ter, was identified in 3 normal individuals and 1 patient with Stargardt' s disease, suggesting its nonpathogenicity. Arg677Ter is expected to lead to large disruptions of the encoded protein.Conclusions. The nonpathogenicity of Argl933Ter indicates that the C - terminal 224 residues of RPl protein may be not critical for RP1. The most C - terminal truncation previously reported was due to Tyr1053 (1 -bp del) and occurred in RP patients. Thus RP can be caused by reduction in the level of the region of RPl protein after codon 1052 but before 1933. To ascertain such a proposition, genotypes of more RP patients may reveal more RP causative mutations and more sequence alterations different than those of other ethnic groups.

A disputed evidence on obesity:comparison of the effects of Rcan2^(-/-) and Rps6kb1^(-/-) mutations on growth and body weight in C57BL/6J mice

It is widely accepted that body weight and adipose mass are tightly regulated by homeostatic mechanisms, in which leptin plays a critical role through hypothalamic pathways, and obesity is a result of homeostatic disorder. However, in C57BL/6J mice, we found that Rcan2 increases food intake and plays an important role in the develop- ment of age- and diet-induced obesity through a leptin-independent mechanism. RCAN2 was initially identified as a thyroid hormone （T3）-responsive gene in human fibroblasts. Expression of RCAN2 is regulated by T3 through the PI3K-Akt/PKB-mTOR-Rps6kbl signaling pathway. Intriguingly, both Rcan2-/- and Rps6kb1-/- mutations were re- ported to result in lean phenotypes in mice. In this study we compared the effects of these two mutations on growth and body weight in C57BL/6J mice. We observed reduced body weight and lower fat mass in both Rcan2-/- and Rps6kb1-/- mice compared to the wild-type mice, and we reported other differences unique to either the Rcan2-/- or Rps6kb1-/- mice. Firstly, loss of Rcan2 does not directly alter body length; however, Rcan2-/- mice exhibit reduced food intake. In contrast, Rps6kb1-/- mice exhibit abnormal embryonic development, which leads to smaller body size and reduced food intake in adulthood. Secondly, when fed a normal chow diet, Rcan2-/- mice weigh significantly more than Rps6kb1-/- mice, but both Rcan2-/- and Rps6kbl-/- mice develop similar amounts of epididymal fat. On a high-fat diet, Rcan2-/- mice gain body weight and fat mass at slower rates than Rps6kb1-/- mice. Finally, using the double-knockout mice （Rcan2-/- Rps6kb1-/-）, we demonstrate that concurrent loss of Rcan2and Rps6kbl has an additive effect on body weight reduction in C57BL/6J mice. Our data suggest that Rcan2 and Rps6kbl mutations both affect growth and body weight of mice, though likely through different mechanisms.