[Analysis of Abnormal Genotyping at Amelogenin Locus in Male Individuals]

To investigate the abnormal genotyping and its causes at the Amelogenin locus in male samples.

A total of 23 647 blood samples from unrelated male individuals were analyzed using the STRtyper-21G kit, and 38 samples with abnormal Amelogenin locus were identified. These samples were retested and classified using GlobalFiler^TM and PowerPlex^® 21 kits. Additional sex chromosome STR genotyping and Sanger sequencing were performed for samples with abnormal genotypes. Sequence-tagged site (STS) testing was conducted for samples suspected of Amel-Y microdeletions.

Among above 38 samples, except for Amelogenin locus, all samples showed normal male sex chromosome STR typing. The detection rate of abnormal genotyping was 0.161% (38/23 647), which were categorized into three major types. Among them, 30 cases had Amel-X deletion: 5 cases had C→T mutation at position 372; 2 cases had G→A mutation at position 293; 23 cases had A→G mutation at position 304. There were 2 cases of Amel-Y deletion: 1 case of insertion mutation of TTAA at position 387, and 1 case of microdeletion of the short arm containing Amel-Y. Six cases of abnormal Amel-X/Y peak ratios were identified: using the STRtyper-21G kit, the abnormalities appeared as low Amel-X with absent Amel-Y, normal Amel-X with absent Amel-Y, normal Amel-X with low Amel-Y, respectively. However, retesting with GlobalFiler^TM and PowerPlex^® 21 kits consistently showed normal Amel-X with low Amel-Y. The GlobalFiler^TM profiling showed that the peak heights of Amel-Y were comparable to those of the Y-InDel and DYS391 markers, and no abnormalities were detected by sequencing.

Amelogenin genotyping abnormalities occur at a measurable frequency in the population and are mainly associated with mutations, which can be categorized as Amel-X deletion, Amel-Y deletion, and Amel-X/Y peak ratio abnormality. Regarding normal Amel-X peaks with lower Amel-Y peaks, the possibility of mosaic loss of chromosome Y (mLOY) in samples, which is commonly observed in elderly males, should be considered and given attention.