Table 3.

Gene and protein alteration of known genes causing X-linked nonsyndromic hearing impairment.

Locus name	Gene	Protein altered
DFNX1 (DFN2)	PRPS1	The phosphoribosyl pyrophosphate synthetase 1 gene codes for an enzyme by the same name (PRPP synthetase 1). This enzyme helps produce a molecule called phosphoribosyl pyrophosphate (PRPP). PRPP is important in making purine and pyramidine nucleotides. The exact mechanism by which bit is involved in causing deafness is not known.
DFNX2 (DFN3)	POU3F4	The POU3F4 gene encodes a protein called POU domain, class 3, transcription factor 4 whose function is unknown.
DFNX4 (DFN6)	SMPX	SMPX is the Small Muscle Protein, X linked is coded for by the gene. Its role in causing deafness is not clear.