CYP17A1 Intron Mutation Causing Cryptic Splicing in 17α-Hydroxylase Deficiency

Abstract

17α-hydroxylase/17, 20-lyase deficiency (17OHD) is an autosomal recessive disease causing congenital adrenal hyperplasia and a rare cause of hypertension with hypokalemia. The CYP17A1 gene mutation leads to 17OHD and its clinical features. We described an 18 y/o female with clinical features of 17α-hydroxylase/17, 20-lyase deficiency and characterized the functional consequences of an intronic CYP17A1 mutation. The coding regions and flanking intronic bases of the CYP17A1 gene were amplified by PCR and sequenced. The patient is a compound heterozygote for the previously described p.R358X and IVS1 +2T>C mutations. A first intron splice donor site mutation was re-created in minigene and full-length expression vectors. Pre-mRNA splicing of the variant CYP17A1 intron was studied in transfected cells and in a transformed lymphoblastoid cell line. When the full-length CYP17A1 gene and minigene containing the intronic mutation was expressed in transfected cells, the majority (>90%) of mRNA transcripts were incorrectly spliced. Only the p.R358X transcript was detected in the EBV-transformed lymphoblastoid cell line. The IVS1 +2T>C mutation abolished most 17α-hydroxylase/17, 20-lyase enzyme activity by aberrant mRNA splicing to an intronic pseudo-exon, causing a frame shift and early termination.

Steroid 17-hydroxylase and 17,20-lyase deficiencies, genetic and pharmacologic

“…Although these mutations can be found throughout the gene, many occur near the C-terminus, emphasizing the importance of even the last 14 amino acids for enzyme activity. Splice site mutations can lead to “exon skipping” and truncated, inactive protein [8, 9]. Some frameshift mutations introduce premature stop codons, which also yield truncated proteins.…”

Alternative Splicing in the Cytochrome P450 Superfamily Expands Protein Diversity to Augment Gene Function and Redirect Human Drug Metabolism

“…Some P450 SNPs are exceedingly rare, occurring in less than 1% of the population. These rare mutations are linked to congenital defects, including glaucoma (CYP1B1; Stoilov et al, 1998;Tanwar et al, 2009;Sheikh et al, 2014), 17-a hydroxylase deficiency (CYP17A1; Yamaguchi et al, 1998;Costa-Santos et al, 2004;Hwang et al, 2011;Qiao et al, 2011), congenital adrenal hyperplasia (CYP21A2; Robins et al, 2006;Lee, 2013;Szabó et al, 2013;Sharaf et al, 2015), spina bifida (CYP26A1; Rat et al, 2006), focal facial dermal dysplasia (CYP26C1; Slavotinek et al, 2013), and cerebrotendinous xanthomatosis (CYP27A1; Garuti et al, 1996;Verrips et al, 1997;Chen et al, 1998;Tian and Zhang, 2011). Other P450 polymorphisms that alter splicing are associated with neurologic and metabolic diseases, including Parkinson's disease (CYP2D6, Denson et al, 2005;CYP2J2, Searles Nielsen et al, 2013), hypertension (CYP4A11, Zhang et al, 2013;CYP17A1, Wang et al, 2011), breast cancer (CYP2D6, Huang et al, 1996;CYP19A1, Kristensen et al, 2000;) colon cancer (CYP2W1, Stenstedt et al, 2012), and lung cancer (CYP2D6, Huang et al, 1997;CYP2F1, Tournel et al, 2007).…”

Rare Missense P450c17 <b><i>(CYP17A1)</i></b> Mutation in Exon 1 as a Cause of 46,XY Disorder of Sexual Development: Implications of Breast Tissue ‘Unresponsiveness' despite Adequate Estradiol Substitution

“…It performs the 17-alpha-hydroxylation of progesterone and pregnenolone to 17-hydroxyprogesterone (17OHP) and 17-hydroxypreg-the amount of enzyme activity left, the phenotypic appearance in males may reach from mild alterations, such as a micropenis or hypospadias, to the full clinical picture of 46,XY disorder of sexual development (DSD) [CostaSantos et al, 2004;Yang et al, 2006]. Usually, these severe cases are only seen with mutations leading to fundamental changes in the topology and function of the enzyme [Yamaguchi et al, 1998;Costa-Santos et al, 2004;Hwang et al, 2011].…”