A novel frameshift mutation in the first exon of the 21-OH gene found in homozygosity in an apparently nonconsanguineous family

Congenital adrenal hyperplasia is most frequently due to steroid 21-hydroxylase (21-OH) deficiency. Due to the existence of a pseudogene in tandem duplicated with the 21-OH gene, asymmetric recombination causes the majority of the molecular defects underlying this deficiency: gene conversions and deletions of the functional gene. Screening for a small array of mutations, those existing in the pseudogene together with deletions, allows the characterization of most mutated alleles, 91% in the Spanish population. We report the case of a boy from a nonconsanguineous family, diagnosed during the neonatal period of a salt-wasting form of the deficiency, in which this screening did not a I low the characterization of the paternal or the maternal allele, This infrequent finding in a nonconsanguineous family was further investigated. Single-strand conformation polymorphism screening for new mutations revealed an abnormally migrating pattern when polymerase chain reaction fragments from 21-OH gene exon 1 of the patient and relatives were analyzed. Upon direct sequencing, the insertion of a T at position 64 (64insT, frameshift generating a stop codon at exon 2) was found in homozygosity in the patient. Microsatellite typing in the HLA region revealed the patient to be homozygous for five markers (heterozygosities 0.62 to 0.74). Apparently this new mutation was generated several generations ago and has been preserved for years. Consanguinity had been discarded for several generations, although both families could be traced back to a small rural area in Navarra (Spain).