The c C T mutation

The c.286C>T mutation identified in subject K20-1 was also reported in other ethnic groups, including Brazilian, French-Canadian, Italian, and Arabs from the United Arab Emirates [20], [21], [22], whereas c.318A>G mutation in subjects K10-1 was previously reported in Asian and Caucasians [13], [23], [24]. In the present study, patients with c.286C>T, c.318A>G and c.929_940del mutations presented with primary amenorrhea, sexual infantilism, severe hypertension and hypokalemia, which are consistent with the absence of enzymatic activities for those mutated proteins [11], [25]. In contrast to the subjects with classical clinical manifestations, subject K17-1 presented with occasional hypertension and hypokalemia, irregular menstruation and some degree of breast and genitalia development. Partial 17OHD was rarely reported [7], [9], [10], [11], [25]. Subject K17-1 harbored a CPI-169 heterozygous mutation, c.1460_1469del and c.1386G>T. The c.1460_1469del mutation yielded an inactive protein [11], whereas c.1386G>T mutation was not reported previously. Our enzymatic activity assays showed that 17alpha-hydroxylase and 17,20-lyase activity for the c.1386G>T mutation was partially reduced to 34.6% and 27%, respectively, which corresponds with clinical manifestations, such as some breast and genitalia development, irregular menstruation and episodic hypertension in subject K17-1.
Conclusion
Acknowledgements The present study would not have been possible without the participation of these patients. We are grateful to Dr. Jie Qiao from Department of Endocrinology, Shanghai Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine for her generously providing the wild-type CYP17A1 plasmid as a gift. This study is supported by the grants from the National Nature Science Foundation (Nos. 81000320, 81000319) and the Shanghai Committee for Science and Technology (No. 09DJ1400402).
Introduction 21-Hydroxylase deficiency (21-OHD) is the most common form of congenital adrenal hyperplasia and is caused by mutations in the CYP21A2 gene [1]. The most characteristic biochemical abnormality in 21-OHD is the elevation of 17α-hydroxyprogesterone (17-OHP), the main substrate for CYP21A2 in the glucocorticoid pathway. A cardinal feature of classic 21-OHD in newborn females is genital virilisation [1]. 17-OHP can be metabolised to dihydrotestosterone (DHT) via androstenedione (Δ4A) and testosterone (T) directly by the 17,20-lyase activity of CYP17A1 through the classical Δ4 pathway or via 17α-hydroxypregnenolone (17OH-Preg) and dehydroepiandrosterone (DHEA) through the classical Δ5 pathway, as well as through an alternative route that bypasses DHEA, Δ4A and T as intermediates (Fig. 1) [2], [3], [4]. In this alternative ‘backdoor’ pathway, 17-OHP is converted with high activity to 17α-hydroxyallopregnanolone (5α-17HP; 5α-pregnane-3α,17α-diol-20-on, also known as pdiol) by sequential 5α-reductase and 3α-hydroxysteroid dehydrogenase (HSD) activities. Thus, two enzymes, namely the 5α-reductase and CYP17A1, compete for their substrate 17-OHP (Fig. 1). The 17,20-lyase activity of CYP17A1 regulates both the conversion of 17-OHP and 17OH-Preg to Δ4A and DHEA in the classical Δ4 and Δ5 pathways as well as the conversion of 17α-hydroxyallopregnanolone into androsterone in the alternative backdoor pathway (Fig. 1) [2], [3], [4], [5]. Importantly, 5α-17HP is a better substrate for CYP17A1 than 17-OHP and even 17OH-Preg [6]. The 17,20-lyase reactions are dependent upon cytochrome b5 for maximal activity [7], [8]. Cytochrome b5 stimulates the classical pathway reaction rates by over 10-fold; however, CYP17A1 rapidly converts 5α-17HP to androsterone in the alternative backdoor pathway even in the absence of cytochrome b5 and the addition of cytochrome b5 stimulates the 17,20-lyase reaction only 3-fold [6].
Patients and methods
Results