ianroo

Minireview:
What are the disease phenotypes associated with mutations in your assigned gene? Give 
an example of a specific mutation that is known to alter protein function and that may 
lead to a specific disease phenotype? Briefly describe how this change in the amino 
acid sequence of this protein leads to this disease phenotype? Describe and cite a recent 
paper (2002-present) that addresses research that is being performed in this field. 
(750 words max) 

Written by Hsinwei Hu.

Structure and Function
The CYP21A2 gene encodes for the enzyme steroid 21-hydroxylase (21-OH), which is a member of the cytochrome P450 family of enzymes. The P450 family enzymes are monooxygenases that responsible for breaking down drugs by oxidative degradation, and the synthesis of cholesterol and some steroid hormones and fats (1). The sequences of P450 members varies, but they all share three core domains ?a coiled eander?serves as the heme-binding loop, a four-helix bundle as proton-transfer groove, and two sets of beta-sheets (2). The function of 21-OH is to activate the adrenal glands on the top of kidneys, to convert cholesterol into cortisol and aldosterone, two steroid hormones that maintain blood sugar levels, stress defending, balance of salt and water in blood stream which affects blood pressure (1). Also, the precursor molecule 17-hydroxyprogesterone (17-OHP) to cortisol can be converted into androgen, a male hormone normally responsible for the appearance of secondary sex characteristics in males (1). 

Mutation and Associated Diseases
A common mutative disease associates with this CYP21A2 gene is the Congenital adrenal hyperplasia (CAH), an autosomal recessive, endocrinological disease, due to defective over-production of 17-OHP, which in turns being converted into androgen and leads to androgen excess. The proposed mutation is the exchange or conversion event of DNA between the CYP21A2 with a nearby pseudogene CYP21A1P (a similar but nonfunctional piece of DNA), which causes the reading frame shift and thus codes for non-functional proteins (3). The four major types of syndrome of CAH are salt-wasting (SW) (almost no enzyme activity), caused by a series mutation of Ile-Val-Glu-Met234-238 into Asn-Glu-Glu-Lys; simple virilizing (SV) (about only 2% enzyme activity), caused by a single amino acid substitution of Ile172 into Asn; non-classic (NC) (about 10%-20% activity), caused by single amino acid change of Val281 into Leu (9), and cryptic (asymptomatic) (4, 7). The SW is due to the lack of aldosterone production, so the kidneys is unavailable to re-absorb sodium (3). SV is often found in female fetuses. Virilization is the development of male secondary sex characteristics in the females (6), due to the androgen excess from the 17-OHP that failed to be converted into 11-deoxycortisol, typically in adrenal glands. Female patients with virilism show sexes ambiguity of external genitalia at birth, and later on with masculinization (a development of male characteristics). However, the development internal reproductive organs such as uterus and overies are normal (3). NC shows the moderate amount of the 21-OH, and patients of this type show androgen excess after birth. (3).

Review of Recent Research
Recently, Cukier et al. (10) performed an experiment using the non-radioactive labeled probe to detect the mutations in CYP21A2. The main purpose is to establish an accurate way which requires less amount of DNA sample and the use of biotin-labeling, to replace the hazardous use of radioactive-labeling material which causes pollution and also requires more professional personnel to handle. This method combines the use of a biotin probe, the DNA hybridization with restriction enzyme (Taq I), and gel electrophoresis to analyze the final result. In the 42 CAH patients' DNA samples they've studied with this biotin-labeling method, theye found large gene conversion and deletion patterns, and the results were very similar to the previous data from the radioactive ways. As a result, the concluded that this biotin-labeling is an efficient, accurate way not only requires less amount of DNA sample but also avoids the hazardous radioactive wastes, despite the fact that it a little bit more arduous. They also envision that, since non-radioactive techniques are already being used to analyze other genes, this method could be an advance in the detection of CYP21A2 gene.

References
1.Genetics Home Reference: Gene CYP21A2
2.Sanger Institute: Pfam entry p450, accession #PF00067
3.Genetics Home Reference: 21-hydroxylase deficiency
4.OMIM #201910: ADRENAL HYPERPLASIA, CONGENITAL, DUE TO 21-HYDROXYLASE DEFICIENCY
5.GeneCards: cytochrome P450, family 21, subfamily A, polypeptide 2
6.Mesh: virilism
7.Speiser PW, Dupont J, Zhu D, Serrat J, Buegeleisen M, Tusie-Luna MT, Lesser M, New MI, White PC. Disease expression and molecular genotype in congenital adrenal hyperplasia due to 21-hydroxylase deficiency. 1992 Aug;90(2):584-95
8.Globerman H, Amor M, Parker KL, New MI, White PC. Nonsense mutation causing steroid 21-hydroxylase deficiency. 1988 Jul;82(1):139-44.
9.Tusie-Luna MT, Traktman P, White PC. Determination of functional effects of mutations in the steroid 21-hydroxylase gene (CYP21) using recombinant vaccinia virus. Dec 5;265(34):20916-22.
10.Priscilla Cukier; Tania A. S. S. Bachega; Berenice B. Mendonca; Ana Elisa C. Billerbeck. Use of nonradioactive labeling to detect large gene rearrangements in 21-hydroxylase deficiency. Rev. Hosp. Clin. vol.59 no.6  Sao Paulo  2004