ABSTRACT
Mutations in the Emopamil-binding protein (EBP) gene cause X-linked dominant chondrodysplasia punctata 2 (CDPX2), a disorder in which at least 95% of liveborn individuals are female and male intrauterine lethality is assumed. Several affected males with mutations in EBP have been reported. These males exhibit a phenotype similar to CDPX2 due to either somatic mosaicism or a 47, XXY karyotype in association with a null EBP allele. Alternatively, affected males may exhibit a distinct phenotype if they are hemizygous for a hypomorphic allele of EBP. Recently, we described a novel X-linked phenotype associated with digital abnormalities, intellectual disability and short stature, and mapped it to Xp11.4-p11.21. X-exome sequencing was performed to identify the mutated gene responsible for this phenotype. A novel missense variant, c.224T>A (p.I75N), was identified in EBP. SIFT and PolyPhen-2 predicted this change to be deleterious. The pathogenicity of this variant was subsequently supported by increased plasma levels of 8(9)-cholestenol in the proband and his mother. The molecular and biochemical evidence convincingly supports the pathogenicity and association of the p.I75N mutation with this newly described phenotype. This study expands the current phenotypic spectrum of males with hypomorphic EBP mutations and supports to the hypothesis that there exists an X-linked recessive entity independent of CDPX2.
Subject(s)
Chondrodysplasia Punctata/diagnosis , Genetic Diseases, X-Linked/diagnosis , Genetic Diseases, X-Linked/genetics , Mutation , Steroid Isomerases/genetics , Diagnosis, Differential , Exome , Genetic Association Studies , Genotype , High-Throughput Nucleotide Sequencing , Humans , Male , Pedigree , PhenotypeABSTRACT
The family observed in this study included affected males and asymptomatic females. The patients shared specific digital abnormalities including postaxial polydactyly, cutaneous syndactyly, and brachydactyly. In addition, the patients exhibited mild-to-moderate intellectual disability and short stature coupled with microbrachycephaly, scoliosis, and cerebellar and renal hypoplasia. No chromosomal alterations or copy number variations were found in the index case. The genetic linkage analysis, which focused on the X chromosome, and the haplotype analysis detected a ~15.74 Mb candidate region located at Xp11.4-p11.21 with a LOD score of 4.8. Additionally, half of the mothers showed skewed X-inactivation, while the other mothers exhibited random inactivation patterns. The candidate region includes 28 protein-encoding genes that have not yet been implicated in human disorders. We speculate that the observed phenotype is compatible with a monogenic disorder in which the mutant gene plays a significant role during embryonic development. Based on the patients' clinical features, image studies, pedigree, chromosome location, and X-inactivation studies in the mothers, we propose that this family has a novel, specific syndrome with an X-linked recessive mode of inheritance.
Subject(s)
Abnormalities, Multiple/genetics , Chromosomes, Human, X , Dwarfism/genetics , Fingers/abnormalities , Intellectual Disability/genetics , Toes/abnormalities , Abnormalities, Multiple/diagnosis , Adult , Chromosome Mapping , Diagnosis, Differential , Dwarfism/diagnosis , Female , Genes, Recessive , Genes, X-Linked , Haplotypes , Humans , Intellectual Disability/diagnosis , Lod Score , Male , Mexico , Middle Aged , Molecular Diagnostic Techniques , Pedigree , Phenotype , X Chromosome Inactivation , Young AdultABSTRACT
RNA interference (RNAi) is a double-stranded RNA (dsRNA)-triggered mechanism for suppressing gene expression, which is conserved in evolution and has emerged as a powerful tool to study gene function. Rotaviruses, the leading cause of severe diarrhea in young children, are formed by three concentric layers of protein, and a genome composed of 11 segments of dsRNA. Here, we show that the RNAi machinery can be triggered to silence rotavirus gene expression by sequence-specific short interfering RNAs (siRNAs). RNAi is also useful for the study of the virus-cell interactions, through the silencing of cellular genes that are potentially important for the replication of the virus. Interestingly, while the translation of mRNAs is readily stopped by the RNAi machinery, the viral transcripts involved in virus genome replication do not seem to be susceptible to RNAi. Since gene silencing by RNAi is very efficient and specific, this system could become a novel therapeutic approach for rotavirus and other virus infections, once efficient methods for in vivo delivery of siRNAs are developed. Although the use of RNAi as an antiviral therapeutic tool remains to be demonstrated, there is no doubt that this technology will influence drastically the way postgenomic virus research is conducted.
