Quantitative sequence analysis of FBN1 premature termination codons provides evidence for incomplete NMD in leukocytes.

We improved, evaluated, and used Sanger sequencing for quantification of single nucleotide polymorphism (SNP) variants in transcripts and gDNA samples. This improved assay resulted in highly reproducible relative allele frequencies (e.g., for a heterozygous gDNA 50.0+/-1.4%, and for a missense mutation-bearing transcript 46.9+/-3.7%) with a lower detection limit of 3-9%. It provided excellent accuracy and linear correlation between expected and observed relative allele frequencies. This sequencing assay, which can also be used for the quantification of copy number variations (CNVs), methylations, mosaicisms, and DNA pools, enabled us to analyze transcripts of the FBN1 gene in fibroblasts and blood samples of patients with suspected Marfan syndrome not only qualitatively but also quantitatively. We report a total of 18 novel and 19 known FBN1 sequence variants leading to a premature termination codon (PTC), 26 of which we analyzed by quantitative sequencing both at gDNA and cDNA levels. The relative amounts of PTC-containing FBN1 transcripts in fresh and PAXgene-stabilized blood samples were significantly higher (33.0+/-3.9% to 80.0+/-7.2%) than those detected in affected fibroblasts with inhibition of nonsense-mediated mRNA decay (NMD) (11.0+/-2.1% to 25.0+/-1.8%), whereas in fibroblasts without NMD inhibition no mutant alleles could be detected. These results provide evidence for incomplete NMD in leukocytes and have particular importance for RNA-based analyses not only in FBN1 but also in other genes.

Overexpression of RPGR leads to male infertility in mice due to defects in flagellar assembly.

Male infertility is one possible consequence of a group of disorders arising from dysfunction of cilia. Ciliopathies include primary ciliary dyskinesia, polycystic kidney disease, Usher syndrome, nephronophthisis, Bardet-Biedl syndrome, Alstrom syndrome, and Meckel-Gruber syndrome as well as some forms of retinal degenerations. Mutations in the retinitis pigmentosa GTPase regulator gene (RPGR) are best known for leading to retinal degeneration but have also been associated with ciliary dysfunctions affecting other tissues. To further study the involvement of RPGR in ciliopathies, transgenic mouse lines overexpressing RPGR were generated. Animals carrying the transgene in varying copy numbers were investigated. We found that infertility due to aberrant spermatozoa correlated with increased copy numbers. In animals with moderately increased gene copies of Rpgr, structural disorganization in the flagellar midpiece, outer dense fibers, and fibrous sheath was apparent. In contrast, in animals with high copy numbers, condensed sperm heads were present, but the flagellum was absent in the vast majority of spermatozoa, although early steps of flagellar biogenesis were observed. This complexity of defects in flagellar assembly suggests a role of RPGR in intraflagellar transport processes.