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Patients with adrenal insufficiency, genital anomalies and bony malformations resembling the Antley- Bixler syndrome (a craniosynostosis syndrome), are likely to have P450 oxidoreductase (POR) deficiency. Since our first report in 2004, about 26 recessive POR mutations have been identified in 50 patients. POR is the obligate electron donor to all microsomal (type II) P450 enzymes, including the steroidogenic enzymes CYP17A1, CYP21A2 and CYP19A1. POR deficiency may cause disordered sexual development manifested as genital undervirilization in 46,XY newborns as well as overvirilization in those who are 46,XX. This may be explained by impaired aromatization of fetal androgens which may also lead to maternal virilization and low urinary estriol levels during pregnancy. A role for the alternate 'backdoor' pathway of androgen biosynthesis, leading to dihydrotestosterone production bypassing androstenedione and testosterone, has been suggested in POR deficiency but remains unclear. POR variants may play an important role in drug metabolism, as most drugs are metabolized by hepatic microsomal P450 enzymes. However, functional assays studying the effects of specific POR mutations on steroidogenesis showed that several POR variants impaired CYP17A1, CYP21A2 and CYP19A1 activities to different degrees, indicating that each POR variant must be studied separately for each potential target P450 enzyme. Thus, the impact of POR mutations on drug metabolism by hepatic P450s requires further investigation.

Cytochrome P450 proteins are involved in metabolism of drugs and xenobiotics. In the endoplasmic reticulum a single nicotinamide adenine dinucleotide phosphate (NADPH) P450 oxidoreductase (POR) supplies electrons to all microsomal P450s for catalytic activity. POR is a flavoprotein that contains both flavin mononucleotide and flavin adenine dinucleotide as cofactors and uses NADPH as the source of electrons. We have recently reported a number of POR mutations in the patients with disordered steroidogenesis. In the first report we had described missense mutations (A287P, R457H, V492E, C569Y, and V608F) identified in four patients with defects in steroid production. Each POR variant was produced as recombinant N-27 form of the enzyme in bacteria and as full-length form in yeast. Membranes from bacteria or yeast expressing normal or variant POR were purified and their activities were characterized in cytochrome c and CYP17A1 assays. Later we have published a larger study that described a whole range of POR mutations and characterized the mutants/polymorphisms A115V, T142A, M263V, Y459H, A503V, G539R, L565P, R616X, V631I, and F646del from the sequencing of patient DNA. We also studied POR variants Y181D, P228L, R316W, G413S, and G504R that were available in public databases or published literature. Three-dimensional structure of rat POR is known and we have used this structure to deduce the structure-function correlation of POR mutations in human. The missense mutations found in patients with disordered steroidogenesis are generally in the co-factor binding and functionally important domains of POR and the apparent polymorphisms are found in regions with lesser structural importance. A variation in POR can alter the activity of all microsomal P450s, and therefore, can affect the metabolism of drugs and xenobiotics even when the P450s involved are otherwise normal. It is important to study the genetic and biochemical basis of POR variants in human population to gain information about possible differences in P450 mediated reactions among the individuals carrying a variant or polymorphic form of POR that could impact their metabolism.

OBJECTIVE: The previously described c655G>A mutation of the human cytochrome P450 aromatase gene (P450aro, CYP19) results in aberrant splicing due to disruption of a donor splice site. To explain the phenotype of partial aromatase deficiency observed in a female patient described with this mutation, molecular consequences of the c655G>A mutation were investigated. DESIGN: To investigate whether the c655G>A mutation causes an aberrant spliced mRNA lacking exon 5 (-Ex5), P450aro RNA was analysed from the patient's lymphocytes by reverse transcription polymerase chain reaction (RT-PCR) and by splicing assays performed in Y1 cells transfected with a P450aro -Ex5 expression vector. Aromatase activity of the c655G>A mutant was predicted by three dimensional (3D) protein modelling studies and analysed in transiently transfected Y1 cells. Exon 5 might be predicted as a poorly defined exon suggesting a susceptibility to both splicing mutations and physiological alternative splicing events. Therefore, expression of the -Ex5 mRNA was also assessed as a possibly naturally occurring alternative splicing transcript in normal human steroidogenic tissues. PATIENTS: An aromatase deficient girl was born with ambiguous genitalia. Elevated serum LH, FSH and androgens, as well as cystic ovaries, were found during prepuberty. At the age of 8.4 years, spontaneous breast development and a 194.6 pmol/l serum oestradiol level was observed. RESULTS: The -Ex5 mRNA was found in lymphocytes of the P450aro deficient girl and her father, who was a carrier of the mutation. Mutant minigene expression resulted in complete exon 5 skipping. As expected from 3D protein modelling, -Ex5 cDNA expression in Y1 cells resulted in loss of P450aro activity. In addition, the -Ex5 mRNA was present in placenta, prepubertal testis and adrenal tissues. CONCLUSIONS: Alternative splicing of exon 5 of the CYP19 gene occurs in the wild type (WT) as well as in the c655G>A mutant. We speculate that for the WT it might function as a regulatory mechanism for aromatization, whereas for the mutant a relative prevalence of the shorter over the full-length protein might explain the phenotype of partial aromatase deficiency.

Deficient activities of multiple steroidogenic enzymes have been reported without and with Antley-Bixler syndrome (ABS), but mutations of corresponding cytochrome P450 enzymes have not been found. We identified mutations in POR, encoding P450 oxidoreductase, the obligate electron donor for these enzymes, in a woman with amenorrhea and three children with ABS, even though knock-out of POR is embryonically lethal in mice. Mutations of POR also affect drug-metabolizing P450 enzymes, explaining the association of ABS with maternal fluconazole ingestion.

Major blood stage antimalarial drugs like chloroquine and artemisinin target the heme detoxification process of the malaria parasite. Hemozoin formation reactions in vitro using the Plasmodium falciparum histidine-rich protein-2 (Pfhrp-2), lipids, and auto-catalysis are slow and could not explain the speed of detoxification needed for parasite survival. Here, we show that malarial hemozoin formation is a coordinated two component process involving both lipids and histidine-rich proteins. Hemozoin formation efficiency in vitro is 1-2% with Pfhrp-2 and 0.25-0.5% with lipids. We added lipids after 9h in a 12h Pfhrp-2 mediated reaction that resulted in sixfold increase in hemozoin formation. However, a lipid mediated reaction in which Pfhrp-2 was added after 9h produced only twofold increase in hemozoin production compared to the reaction with Pfhrp-2 alone. Synthetic peptides corresponding to the Pfhrp-2 heme binding sequences, based on repeats of AHHAAD, neither alone nor in combination with lipids were able to generate hemozoin in vitro. These results indicate that hemozoin formation in malaria parasite involves both the lipids and the scaffolding proteins. Histidine-rich proteins might facilitate hemozoin formation by binding with a large number of heme molecules, and facilitating the dimer formation involving iron-carboxylate bond between two heme molecules, and lipids may then subsequently assist the mechanism of long chain formation, held together by hydrogen bonds or through extensive networking of hydrogen bonds.

The haem detoxification pathway of the malaria parasite Plasmodiumfalciparum is a potential biochemical target for drug development. Free haem, released after haemoglobin degradation, is polymerized by the parasite to form haemozoin pigment. Plasmodiumfalciparum histidine-rich protein-2 (Pfhrp-2) has been implicated as the catalytic scaffold for detoxification of haem in the malaria parasite. Previously we have shown that a hexapeptide repeat sequence (Ala-His-His-Ala-Ala-Asp), which appears 33 times in Pfhrp-2, may be the major haem binding site in this protein. The haem binding studies carried out by ourselves indicate that up to 18 equivalents of haem could be bound by this protein with an observed Kd of 0.94µM. Absorbance spectroscopy provides evidence that chloroquine is capable of extracting haem bound to Pfhrp-2. This was supported by the Kd value, of 37nM, observed for the haem-chloroquine complex. The native PAGE studies reveal that the formation of the haem-Pfhrp-2 complex is disrupted by chloroquine. These results indicate that chloroquine may be acting by inhibiting haem detoxification/binding to Pfhrp-2. Moreover, the higher affinity of chloroquine for haem than Pfhrp-2 suggests a possible mechanism of action for chloroquine; it may remove the haem bound to Pfhrp-2 and form a complex that is toxic to the parasite.

Malaria parasite digests hemoglobin and utilizes the globin part for its nutritional requirements. Heme released as a byproduct of hemoglobin degradation is detoxified by polymerization into a crystalline, insoluble pigment, known as hemozoin. We have identified a novel reaction of depolymerization of hemozoin to heme. This reaction is initiated by the interaction of blood schizonticidal antimalarial drugs with the malarial hemozoin. The reaction has been confirmed, with the purified hemozoin as well as the lysate of the malaria parasite. Pigment breakdown was studied by infrared spectroscopy, thin-layer chromatography and spectrophotometric analysis. It was complete within 2 h of drug exposure, which explains the selective sensitivity of late stages (trophozoites and schizonts) of malarial parasites loaded with the hemozoin pigment to the toxic action of these drugs. It is suggested that the failure of the parasite heme detoxification system due to this reaction results in the accumulation of toxic heme, which alone, or complexed with the antimalarial leads to the death of malaria parasite.© 1997 Federation of European Biochemical Societies. All rights reserved.

Malaria parasite detoxifies free haem, released as a result of haemoglobin digestion, by converting it into an stable, crystalline, black brown pigment known as ‘malaria pigment’ or ‘haemozoin’. Earlier studies have demonstrated the involvement of a parasite-specific enzyme ‘haem polymerase’ in the formation of haemozoin. However, recently it has been proposed that the polymerization of haem may be a spontaneous process that could take place by incubation of haematin with carboxylic acids (pH 4.2–5.0) even without presence of any parasitic or biological component (FEBS Letters, 352, 54–57 (1994)). Here we report that no spontaneous haem polymerization occurs at physiological conditions and the product described in the study mentioned above is not haemozoin/β-haematin (haem polymer) as characterized by us on the basis of solubility characteristics and thin layer chromatography. The infra-red spectroscopic analysis of the product formed though exhibits the bands corresponding to formation of iron-carboxylate bond, similar to that in haemozoin/β-haematin, but was identified as haem-acid adduct. Thus polymerization of haem may not occur spontaneously under the reaction conditions corresponding to food vacuoles of the malarial parasite, the physiological site of haemozoin formation.

Objective Mutations in melanocortin receptor 2 (MC2R) and its related melanocortin receptor accessory protein (MRAP) cause familial glucocorticoid deficiency. We identified a novel MC2R mutation, K289fs. This unique mutation in the C terminus of MC2R is located in the intracellular part of the protein for which the exact function is unknown. Setting A 6-wk-old boy presented with severe hypoglycemia, unmeasurable cortisol, and grossly elevated ACTH but normal electrolytes. Genetic analysis revealed homozygote K289fs mutation in MC2R. His parents and siblings were heterozygous but phenotypically normal. Intervention and Results The role of the C terminus of MC2R was studied in two cell systems. Because the K289fs mutant changes the last eight amino acids of the protein and leads to protein elongation, wild-type MC2R and C-terminally mutated constructs were tested for activity to respond to ACTH in an OS3 cell-based reporter assay. Wild-type and alanine-substituted constructs responded normally to ACTH. By contrast K289fs and M290X had a total loss of activity. Cell surface assays and confocal localization studies revealed that K289fs and M290X receptors were not found at the cell surface, indicating that their transport from the endoplasmic reticulum to the cell membrane is disrupted. Interestingly, coimmunoprecipitation experiments showed no alteration in the interaction of mutant MC2R with MRAP, suggesting that interaction between these two proteins does not guarantee normal localization. Conclusions Loss of the C terminus of MC2R impairs cell surface expression and ACTH sensitivity but does not disrupt interaction of MC2R with MRAP. These findings highlight the extreme sensitivity of MC2R to structural disruption.

Background P450 aromatase (CYP19A1) is essential for the biosynthesis of estrogens from androgen precursors. Mutations in the coding region of CYP19A1 lead to autosomal recessive aromatase deficiency. To date over 20 subjects have been reported with aromatase deficiency which may manifest during fetal life with maternal virilization and virilization of the external genitalia of a female fetus due to low aromatase activity in the steroid metabolizing fetal–placental unit and thus high androgen levels. During infancy, girls often have ovarian cysts and thereafter fail to enter puberty showing signs of variable degree of androgen excess. Moreover, impact on growth, skeletal maturation and other metabolic parameters is seen in both sexes. Objective and hypothesis We found a novel homozygous CYP19A1 mutation in a 46,XX girl who was born at term to consanguineous parents. Although the mother did not virilize during pregnancy, the baby was found to have a complex genital anomaly at birth (enlarged genital tubercle, fusion of labioscrotal folds) with elevated androgens at birth, normalizing thereafter. Presence of 46,XX karyotype and female internal genital organs (uterus, vagina) together with biochemical findings and follow-up showing regression of clitoral hypertrophy, as well as elevated FSH suggested aromatase deficiency. Interestingly, her older brother presented with mild hypospadias and bilateral cryptorchidism and was found to carry the same homozygous CYP19A1 mutation. To confirm the clinical diagnosis, genetic, functional and computational studies were performed. Methods and results Genetic analysis revealed a homozygous R192H mutation in the CYP19A1 gene. This novel mutation was characterized for its enzymatic activity (Km, Vmax) in a cell model and found to have markedly reduced catalytic activity when compared to wild-type aromatase; thus explaining the phenotype. Computational studies suggest that R192H disrupts the substrate access channel in CYP19A1 that may affect binding of substrates and exit of catalytic products. Conclusion R192H is a novel CYP19A1 mutation which causes a severe phenotype of aromatase deficiency in a 46,XX newborn and maybe hypospadias and cryptorchidism in a 46,XY, but no maternal androgen excess during pregnancy.

The orteronel, abiraterone and galeterone, which were developed to treat castration resistant prostate cancer, inhibit 17,20 lyase activity but little is known about their effects on adrenal androgen biosynthesis. We studied the effect of several inhibitors and found that orteronel was selective towards 17,20 lyase activity than abiraterone and galeterone. Gene expression analysis showed that galeterone altered the expression of HSD3B2 but orteronel did not change the expression of HSD3B2, CYP17A1 and AKR1C3. The CYP19A1 activity was not inhibited except by compound IV which lowered activity by 23%. Surprisingly abiraterone caused complete blockade of CYP21A2 activity. Analysis of steroid metabolome by gas chromatography - mass spectrometry revealed changes in steroid levels caused by different inhibitors. We can conclude that orteronel is a highly specific inhibitor of 17,20 lyase activity. The discovery of these specific drug actions on steroidogenic enzyme activities would be valuable for understanding the regulation of androgens.

© 2015 Elsevier B.V. FGFRL1 is a single pass transmembrane protein with three extracellular Ig domains. When overexpressed in CHO cells or related cell types it induces cell cell fusion and formation of large multinucleated syncytia. For this fusion promoting activity only the membrane proximal Ig domain (Ig3) and the transmembrane domain are required. It does not matter whether the transmembrane domain is derived from FGFRL1 or from another receptor but the distance of the Ig3 domain to the membrane is crucial. Fusion can be inhibited with soluble recombinant proteins comprising the Ig1 Ig2 Ig3 or the Ig2 Ig3 domains as well as with monoclonal antibodies directed against Ig3. Mutational analysis reveals a hydrophobic site in Ig3 that is required for fusion. If a single amino acid from this site is mutated fusion is abolished. The site is located on a ß sheet which is part of a larger ß barrel as predicted by computer modeling of the 3D structure of FGFRL1. It is possible that this site interacts with a target protein of neighboring cells to trigger cell cell fusion.

Context: Steroidogenic factor-1 (SF-1/NR5A1) is a nuclear receptor that regulates adrenal and reproductive development and function. NR5A1 mutations have been detected in 46,XY individuals with disorders of sexual development (DSD) but apparently normal adrenal function and in 46,XX women with normal sexual development yet primary ovarian insufficiency (POI). Objective: A group of 100 46,XY DSD and two POI was studied for NR5A1 mutations and their impact. Design: Clinical, biochemical, histological, genetic, and functional characteristics of the patients with NR5A1 mutations are reported. Setting: Patients were referred from different centers in Spain, Switzerland, and Turkey. Histological and genetic studies were performed in Barcelona, Spain. In vitro studies were performed in Bern, Switzerland. Patients: A total of 65 Spanish and 35 Turkish patients with 46,XY DSD and two Swiss 46,XX patients with POI were investigated. Main Outcome: Ten novel heterozygote NR5A1 mutations were detected and characterized (five missense, one nonsense, three frameshift mutations, and one duplication). Results: The novel NR5A1 mutations were tested in vitro by promoter transactivation assays showing grossly reduced activity for mutations in the DNA binding domain and variably reduced activity for other mutations. Dominant negative effect of the mutations was excluded. We found high variability and thus no apparent genotype-structure-function-phenotype correlation. Histological studies of testes revealed vacuolization of Leydig cells due to fat accumulation. Conclusions: SF-1/NR5A1 mutations are frequently found in 46,XY DSD individuals (9%) and manifest with a broad phenotype. Testes histology is characteristic for fat accumulation and degeneration over time, similar to findings observed in patients with lipoid congenital adrenal hyperplasia (due to StAR mutations). Genotype-structure-function-phenotype correlation remains elusive.

Claudins are major components of tight junctions and contribute to the epithelial-harrier function by restricting free diffusion of solutes through the paracellular pathway. We have mapped a new locus for recessive renal magnesium loss on chromosome 1p34.2 and have identified mutations in CLDN19, a member of the claudin multigene family, in patients affected by hypomagnesemia, renal failure, and severe ocular abnormalities. CLDN19 encodes the tight-junction protein claudin-19, and we demonstrate high expression of CLDN19 in renal tubules and the retina. The identified mutations interfere severely with either cell-membrane trafficking or the assembly of the claudin-19 protein. The identification of CLDN19 mutations in patients with chronic renal failure and severe visual impairment supports the fundamental role of claudln-19 for normal renal tubular function and undisturbed organization and development of the retina. © 2006 by The American Society of Human Genetics. All rights reserved., published_or_final_version

Combined partial deficiency of 17alpha-hydroxylase and 21-hydroxylase activities was first described in 1985; however the genes for P450c17 and P450c21 in these patients lack mutations. In 1986 we postulated that this disorder might be due to mutations in P450 oxidoreductase (POR), the flavoprotein that donates electron to these and all other microsomal P450 enzymes, but this hypothesis was not tested until the POR gene sequence became available through the genome database. We found five POR missense mutations in our first four patients. In vitro assays of the activities of these mutations showed that the standard assay of POR activity, reduction of cytochrome c, correlated poorly with the patients' phenotypes, but that assays of POR-supported 17alpha-hydroxylase and 17,20 lyase activities correlated well. POR deficiency is a new disorder of adrenal and gonadal steroidogenesis that affects all microsomal cytochrome P450 enzymes, hence may have important implications for genetic differences in drug metabolism.

Androgen biosynthesis in the human fetus proceeds through the adrenal sex steroid precursor dehydroepiandrosterone, which is converted to testosterone in the gonads, followed by further activation to 5α-dihydrotestosterone in genital skin, thereby facilitating male external genital differentiation. Congenital adrenal hyperplasia due to P450 oxidoreductase deficiency results in disrupted dehydroepiandrosterone biosynthesis, explaining undervirilization in affected boys. However, many affected girls are born virilized, despite low circulating androgens. We hypothesized that this is due to a prenatally active, alternative androgen biosynthesis pathway from 17α-hydroxyprogesterone to 5α-dihydrotestosterone, which bypasses dehydroepiandrosterone and testosterone, with increased activity in congenital adrenal hyperplasia variants associated with 17α-hydroxyprogesterone accumulation. Here we employ explant cultures of human fetal organs (adrenals, gonads, genital skin) from the major period of sexual differentiation and show that alternative pathway androgen biosynthesis is active in the fetus, as assessed by liquid chromatography-tandem mass spectrometry. We found androgen receptor expression in male and female genital skin using immunohistochemistry and demonstrated that both 5α-dihydrotestosterone and adrenal explant culture supernatant induce nuclear translocation of the androgen receptor in female genital skin primary cultures. Analyzing urinary steroid excretion by gas chromatography-mass spectrometry, we show that neonates with P450 oxidoreductase deficiency produce androgens through the alternative androgen pathway during the first weeks of life. We provide quantitative in vitro evidence that the corresponding P450 oxidoreductase mutations predominantly support alternative pathway androgen biosynthesis. These results indicate a key role of alternative pathway androgen biosynthesis in the prenatal virilization of girls affected by congenital adrenal hyperplasia due to P450 oxidoreductase deficiency.

Following embryonic sex determination in which the presence of a Y chromosome drives the differentiation of the primitive bipotential gonad into a testis androgens produced by the fetal testis mediate both the stabilization of structures derived from the Wolffian ducts and the closure of the urogenital sinus resulting in the male phenotype. The indispensable role of androgens is demonstrated by the consequences of human androgen receptor deficiency and androgen receptor knockout mice which have female external genitalia despite the presence of testes and abundant androgens. Two androgens testosterone and dihydrotestosterone (DHT) are needed to produce the human male phenotype [1]. Testosterone produced in the fetal testis reaches the genital skin of the fetal labioscrotal folds where it is converted to DHT by 5a reductase. The resulting DHT induces labioscrotal fusion the development of the phallic urethra and some phallic enlargement. Despite acting through a single androgen receptor distinct roles for testosterone and DHT are shown by 46XY males with 5a reductase deficiency who typically have an open urogenital sinus a perineal urethral orifice a small phallus and chordee [2]. In the “classic” pathway of androgen synthesis dehydroepiandrosterone (DHEA) and androstenedione or androstenediol are key intermediates in the synthesis of testosterone and fetal DHT is produced in situ in its target organ the genital skin where it acts as a paracrine factor (Fig. 4B.1). An alternative or “backdoor” biosynthetic pathway leading to the production of DHT without going through testosterone has been described in marsupials [3–5] and in rodents [67] but the potential relevance of this pathway to human genital masculinization has been unclear. Recent work has established an essential role for this pathway in human male sexual development. Patients with genetic lesions in AKR1C2 a 3a hydroxysteroid dehydrogenase (3a HSD) that participates in the backdoor pathway but not in the classic pathway of testosterone biosynthesis had a disorder of sexual development (DSD) [8]. Several mutations were found and the index family had combined partial disorders of two AKR1C enzymes AKR1C2 and AKR1C4 whereas another patient had 46XY DSD only with disordered AKR1C2. This unique newly described form of DSD establishes that the backdoor pathway is essential for normal male sexual development dramatically revising former views of the mechanisms of normal and pathological masculinization.

Cytochrome P450 oxidoreductase deficiency (PORD; OMIM 613571 and 201750) is the newest form of congenital adrenal hyperplasia (CAH) first described in 2004 [1–5]. By contrast the earliest report of a patient with CAH likely caused by 21 hydroxylase deficiency dates back to 1865 [6]. However it was not until 1905 that the suprarenal capsule was brought into connection with observed anomalies of the sexual organs in CAH [7] and only after 1937 that the altered urinary steroid metabolites were detected [8]. After the identification and synthesis of cortisone in 1949 [9] the field of steroid biochemistry exploded. Over the next decades numerous in vitro and in vivo studies characterized the steroid biosynthetic pathways from cholesterol to its downstream products and the enzymes catalyzing the stepwise conversions leading to mineralocorticoids glucocorticoids and sex steroids [10]. The enzymatic defects of the classic forms of CAH were identified by the late 1960s and during the following genetic era the underlying gene defects were found by the end of the last century. Yet some patients clearly harboring steroid disorders according to their metabolic profile (metabolome) remained and still remain unsolved. Among them were patients presenting with a steroid profile suggesting combined 21 hydroxylase and 17 hydroxylase deficiency for which an index patient had been reported in 1985 [11]. Genetic defects in the genes for CYP21A2 and CYP17A1 were ruled out and a redox partner disease involving cytochrome P450 oxidoreductase (POR) was discussed but not pursued [12]. Only years later sequencing of the POR gene in a Japanese 46XX girl with a metabolome of combined 21 17 hydroxylase deficiency unraveled the underlying genetic defect and led to the characterization of a novel form of CAH caused by defects in POR that provides electrons to all microsomal type II P450s including the steroid enzymes CYP21A2 CYP17A1 and CYP19A11 (Fig. 3H.1). Since then more than 200 POR mutations and polymorphisms including more than 50 amino acid changes in the POR protein have been reported by various laboratories and a POR allele database site has been established (www.cypalleles.ki.se/por.htm) to list mutations and polymorphisms in POR [13–25].

Cytochrome P450 oxidoreductase (POR) supports reactions of microsomal cytochrome P450 which metabolize drugs and steroid hormones. Mutations in POR cause disorders of sexual development. P450 oxidoreductase deficiency (PORD) was initially identified in patients with Antley–Bixler syndrome (ABS) but now it has been established as a separate disorder of sexual development (DSD). Here we are summarizing the work on variations in POR related to metabolism of drugs and xenobiotics. We have compiled mutation data on reported cases of PORD from clinical studies. Mutations found in patients with defective steroid profiles impact metabolism of steroid hormones as well as drugs. Some trends are emerging that establish certain founder mutations in distinct populations, with Japanese (R457H), Caucasian (A287P), and Turkish (399–401) populations showing repeated findings of similar mutations. Most other mutations are found as single occurrences. A large number of different variants in POR gene with more than 130 amino acid changes are now listed in databases. Among the polymorphisms, the A503V is found in about 30% of all alleles but there are some differences across different population groups.