PKHD1L1 , A Gene Involved in the Stereociliary Coat, Causes Autosomal Recessive Nonsyndromic Hearing Loss.

Identification of genes associated with nonsyndromic hearing loss is a crucial endeavor, given the substantial number of individuals who remain without a diagnosis after even the most advanced genetic testing. PKHD1L1 was established as necessary for the formation of the cochlear hair-cell stereociliary coat and causes hearing loss in mice and zebrafish when mutated. We sought to determine if biallelic variants in PKHD1L1 also cause hearing loss in humans. Exome sequencing was performed on DNA of three families segregating autosomal recessive moderate to severe nonsyndromic sensorineural hearing loss. Compound heterozygous missense p.[(Gly129Ser)];p.[(Gly1314Val)], homozygous missense p.(His2479Gln) and nonsense p.(Arg3381Ter) variants were identified in PKHD1L1 that were predicted to be damaging using in silico pathogenicity prediction methods. In vitro functional analysis of two missense variants was performed using purified recombinant PKHD1L1 protein fragments. We then evaluated protein thermodynamic stability with and without the missense variants found in one of the families. In vitro functional assessment indicated that both engineered PKHD1L1 mutant p.(Gly129Ser) and p.(Gly1314Val) constructs significantly reduced the folding and structural stabilities of the expressed protein fragments, providing further evidence to support pathogenicity of these variants. In silico molecular modelling using AlphaFold2 and protein sequence alignment analysis were carried out to further explore potential variant effects on protein folding and stability and exposed key structural features that might suggest PKHD1L1 protein destabilization. Multiple lines of evidence collectively associate PKHD1L1 with nonsyndromic mild-moderate to severe sensorineural hearing loss. PKHD1L1 testing in individuals with mild-moderate hearing loss may identify further affected families.