Mutations intheCYPIIBIgenecausing congenital adrenal hyperplasia andhypertension cluster inexons6,7,and8

Steroid 11,-hydroxylase deficiency (failure toconvert 11-deoxycortisol tocortisol) isthesecond most commoncause ofcongenital adrenal hyperplasia andresults in a hypertensive formofthedisease. The11-hydroxylase enzyme isencoded bytheCYPIIBI geneonchromosome 8q22. Twomutations inCYPIIBIhavepreviously beenreported in patients with11(l-hydroxylase deficiency-Arg-448 -*Hisand a2-bpinsertion incodon 394. Wenowreport eight previously uncharacterized mutations causing this disorder. Seven are point mutations (three nonsense andfourmissense) andoneis asingle basepair deletion causing aframeshift. Wehaveused aninvitro transfection assay toshowthatallfive known missense mutations causing 11l-hydroxylase deficiency abolish enzymatic activity. Inprinciple, deletions ofCYPIIBI could be generated byunequal crossing-over between CYPIIBI andthe adjacent CYP11B2gene, butnosuchdeletions werefound amongthedeficiency alleles inthis study. Sevenofthe10 knownmutations areclustered inexons6-8,anonrandom distribution within thegene. Thismayreflect thelocation of functionally important aminoacid residues within theenzyme oranincreased tendency todevelop mutations within this region ofthegene. Cortisol issynthesized fromcholesterol inthezonafascicu- lata oftheadrenal cortex infiveenzymatic steps. These include cleavage ofthecholesterol side chain toyield preg- nenolone, 3,Bdehydrogenation toprogesterone, andsucces- sive hydroxylations atthe17a,21,and113positions. Inher- ited defects inanyofthese steps causecongenital adrenal hyperplasia, adisorder ofcortisol biosynthesis. Greater than 90%ofcases ofcongenital adrenal hyperplasia areduetoa deficiency insteroid 21-hydroxylase activity (1), whereas mostoftheremaining cases(5-8%) aredueto1113- hydroxylase deficiency (2-4). Inboth 21-andll3-hydroxylase deficiency, theinability of theadrenal cortex tosynthesize cortisol increases secretion ofcorticotropin, resulting inoverproduction ofsteroid pre- cursors thatareshunted intothepathway forandrogen biosynthesis. Female patients with this disorder arethus born withmasculinized external genitalia, andaffected individuals ofbothsexes undergo rapid somatic growth withpremature epiphyseal closure, resulting inshort adult stature. Oneofthe precursors thatcanaccumulate inllf-hydroxylase defi- ciency isdeoxycorticosterone, asteroid withmineralocor- ticoid (sodium-retaining)