Two novel mutations of PAX3 and SOX10 were characterized as genetic causes of Waardenburg Syndrome

Abstract

Background: The objective of this study was to investigate the genetic causes of two probands diagnosed as Waardenburg syndrome (WS type I and IV) from two unrelated Chinese families.

Methods: PAX3 and SOX10 were the main pathogenic genes for WS type I (WS I) and IV (WS IV), respectively; all coding exons of these genes were sequenced on the two probands and their family members. Luciferase reporter assay and co-immunoprecipitation (CO-IP) were conducted to verify potential functional outcomes of the novel mutations.

Results: The first proband is a 9 years old girl diagnosed with WS I. A novel PAX3 heterozygous mutation of c.372-373delGA (p.N125fs) was identified, which results in a frameshift and truncation of PAX3 protein. In family II, a 2 years old girl was diagnosed with WS IV, and Sanger sequencing revealed a de novo SOX10 mutation of c.1114insTGGGGCCCCCACACTACACCGAC (p.Q372fs), a frameshift mutation that extends the amino acid chain of SOX10 protein. Functional studies indicated that the novel mutation of SOX10 had no effects on the interaction of SOX10 and PAX3, but reduced transactivate capacity of melanocyte inducing transcription factor (MITF) promoter. Both PAX3 and SOX10 mutation-induced defects of MITF transcription might contribute to the WS pathogenesis.

Conclusion: We revealed a novel mutation in PAX3 and a de novo mutation in SOX10, which might account for the underlying pathogenesis of WS. This study expands the database of both PAX10 and PAX3 mutations and improves our understanding of the causes of WS.

Keywords: PAX3; SOX10; Waardenburg syndrome; hearing loss.

Figure 1

Clinical phenotypes in family diagnosed with WS I. (a) Iris heterochromia in the eyes, dystopia canthorum, and a pinch of white hair on forehead of the proband; Bright blue irides in eyes and unilateral severe hearing loss of the mother; Iris heterochromia in the left eye of one younger brother with normal hearing; Normal younger brother. (b) Temporal bone CT scan showed that the structure of the inner ear was normal. (c) Bilateral play audiometry (PA) detection. The x‐axis indicates frequency in hertz (Hz) and the y‐axis indicates hearing level in decibels (dB nHL)

Figure 2

Clinical features of the proband diagnosed with WS IV. (a) Iris heterochromia in right eye and premature graying of the hair. (b) CT and MRI showed that the structure of the inner ear and cochlear nerve is normal. (c) Bilateral play audiometry (PA) detection

Figure 3

Pedigree map and PAX3 (NM_181457.3) mutation detection in family I. (a) Pedigree map. Squares and circles denote males and females, respectively. (b) Mutations in exons and primer‐covered introns of all family members. The “*” indicates homozygous mutation. (c) Protein alignment showed that c.372‐373delGA (p.N125fs) induced a frameshift mutation, caused a stop codon at position of 143 amino acid, resulting in truncation of PAX3. (d) The putative schematic representation of PAX3 protein and N125fs mutation, which lead to a large reduction in the PAX3 protein from 479 amino acids to 142 amino acids

Figure 4

Pedigree map and SOX10 (NM_006941.4) sequence in family II. (a) Pedigree map. Squares and circles denote males and females, respectively. (b) Sequence electropherograms showed that c.1114insTGGGGCCCCCACACTACACCGAC (p.Q372fs) was a de novo mutation, which was not inherited from parents. (c) Q372fs caused a frameshift mutation from position of 372 to 508 amino acid, which is 41 amino acids longer than wide‐type SOX10. (d) The putative schematic representation of SOX10 protein and the extended mutants.

Figure 5

Functional analysis of SOX10 Q372fs in A375 cells. (a) Transcriptional capacity of wide‐type SOX10 and its mutant detected by luciferase assays. (b) Protein–protein interaction between PAX3 and wide‐type/mutant SOX10, which is performed by Co‐IP assay using anti‐Flag and anti‐HA antibodies. The “*” indicates p < .05