Leydig cell hypoplasia: cases with new mutations, new polymorphisms and cases without mutations in the luteinizing...

Defective male sex differentiation in patients with hypoplasia of Leydig cells (LCH) is caused by deficient LH receptor signal transduction. To further investigate the variety of LH receptor gene mutations present in LCH patients and their influence on the phenotype, we examined 10 nonrelated patients with the clinical presentation of LCH.

Ten patients with a clinical phenotype of LCH were analysed for mutations in the complete coding region of the LH receptor gene. Exons 1-10 and two overlapping fragments of exon 11 of the LH receptor gene including all intron-exon boundaries were amplified by polymerase chain reaction and sequenced. To screen for frequencies of DNA changes, mutation analysis was performed on 45-59 healthy persons using denaturation high-performance liquid chromatography.

Six new DNA alterations were identified. Three of them appear to be new polymorphisms. A G to C change at the 28th nucleotide of intron 1 on one allele and a heterozygous CGA to CAA transition at codon 124 (R124Q) were found. Both findings in these two patients are polymorphisms that occur with a frequency of 17% and 1.7%, respectively. A silent heterozygous CTA to TTA change at codon 204 was identified. In a patient with micropenis, the analysis revealed a homozygous missense mutation at codon 625 (I625K). As reported previously, this alteration significantly impaired signal transduction and explains the partial phenotype. Finally, in one compound heterozygous patient, two different mutations were discovered. At the polymorphic site in exon 1, a 27-bp insertion (CTG)2 AAG (CTG)5 CAG and a premature stop codon in the transmembrane segment 4 (W491*) were found. Both mutations disrupt signal transduction and explain the complete phenotype of this patient. In five patients, no DNA alterations could be identified.

Three mutations (33 bp insertion in exon 1; W491* and I625K) were identified that explain the phenotype in two patients. In addition, most of the patients with the clinical phenotype of LCH did not have causative mutations, suggesting that changes in other regions of the LH receptor gene, such as the large introns or the promoter region, may be responsible for the majority of cases. Alternatively, the displayed phenotype may be the result of other genetic defects. Our work further underscores the importance of thorough clinical analysis of patients before molecular analysis of a particular gene is performed.