The 21 Hydroxylase adrenal enzime (21-OH) deficiency causes more than 95% of Congenital Adrenal Hyperplasia (CAH). The clinical expression of this deficit is variable, from asintomatic cases to severe virilizations with salt wasters infants Mutations in the gene coding this enzime causes this desease, largely generated by gene conversion from the inactive pseudo gene (CYP21P) to the active one (CYP21) The substitution of a normal nitrogen base (adenine or cytosine) by an abnormal one (guanine) in the gene's intron 2, which generates an aberrant splicing and the loss of enzimatic activity, is the most frecuent mutation in anglosaxon population. The frecuency of this gene's mutations, whoose molecular characterization is really important for early diagnosis and treatment, is unknown in our population Our aim was to determine the frecuency of the intron 2 mutation of this gene in 21-OH deficiency of chilean population

METHODS AND PATIENTS We studied 14 cases belongimg to 14 unrelated families presenting the classical manifestations of this desease (salt wasters and simple virilization), with a diagnosis of a compatible clinical condition associated to 17 OH Progesterone > 50 ng/ml We extracted 10 cc of perifheral blood to every patient to prepare genomic DNA The DNA was amplified by PCR (Polymerase Chain Reaction) using specific primers, obtaining a fragment of 1147 pair of bases (pb) corresponding to exon 1 to 3 of CYP21 gene A new allel specific PCR was made to detect A. C (normal) bases, and G(mutated) The fragments were identified by agarose gel electrophoresis

RESULTS The molecular diagnosis of this mutation was obtain in 4 of 14 patients (28.5%). 3 homocygotes GG (21.4%), and one case (7.1%) compatible with a greater CYP21 gene deletion. In 2 patients (14.3%), only one pathologic allel was identified, both corresponding to heterocygotes AG The 8 remaining patients (57.2%) were homocygotes for the normal AA variant, which implies that the cause of 21-OH deficiency in them, is a different mutation than the affecting the intron 2.

CONCLUSIONS The intron 2 mutation accounts for arround 1/3 of 21-OH deficiency in chilean population. Given the fact that a significant number of patients thus not recognize this ethiology, we recommend expanding the study to detect other mutations in our country FONDECYT PROYECT 1951094