X-linked Alport syndrome (XLAS) is a progressive hereditary kidney disease caused by mutations in the COL4A5 gene encoding the type IV collagen α5 chain. To date, 11 cases having somatic mosaic variants in COL4A5 have been reported; however, all of them involved single-nucleotide variations (SNVs). Here, we report a female XLAS patient with somatic mosaicism identified by copy number variation (CNV) in COL4A5. The case was a 35-year-old female, the mother of the proband, whose only clinical symptom was hematuria. The proband, who was the son of this patient, was diagnosed with XLAS by gene testing, which showed a large hemizygous deletion from exon 3-51 in COL4A5 detected by next-generation sequencing and then confirmed by multiplex ligation-dependent probe amplification (MLPA). Then, MLPA analysis revealed that the female patient had the same deletion with only a 20% copy number reduction compared with a normal female control; she was thus diagnosed with XLAS with somatic mosaicism. CNVs in COL4A5 are relatively rare and, to the best of our knowledge, somatic mosaic variants with CNVs have never been reported. This case clearly featured a germline variant because the patient's son exhibited XLAS. This is thus the first case report on an XLAS patient having CNV in COL4A5 with somatic mosaicism. The obtained findings were very important for the genetic counseling of this family.
Keywords: Copy number variation; Mosaicism; Multiplex ligation-dependent probe amplification; Next-generation sequencing; Type IV collagen α5; X-linked alport syndrome.