Molecular Pathogenesis
NSMI. Despite the fact that a significant number of genes are implicated in NSMI [Matzuk & Lamb 2008], the genetic etiology often goes undiagnosed in the absence of more rigorous characterization of the sperm phenotype that includes measurement of sperm motility parameters such as path velocity, progressive velocity, and track speed. Pathogenic variants in CATSPER1 cause an inherited form of NSMI.
DIS. DIS is a specific syndrome that results from homozygous CATSPER2-STRC deletion. CATSPER1 and CATSPER2 are members of the same gene family.
CATSPER1
Gene structure.
CATSPER1 has a transcript length of 2,634 base pairs (bp) with 12 exons (NM_053054.3). For a detailed summary of gene and protein information, see Table A, Gene.
Pathogenic variants. The pathogenic variants in Table 3 are the only two reported for CATSPER1 to date [reviewed in Hildebrand et al 2010]. These frameshifts in exon 1, identified in two Iranian families, are predicted to result in premature stop codons and complete loss of CATSPER1 protein as a result of nonsense-mediated decay (NMD) or truncated proteins lacking all transmembrane domains and the channel pore.
Based on these data, loss-of-function variants of CATSPER1 are predicted to result in NSMI, although no additional variants have been associated with disease [Avenarius et al 2009]. It is not known whether less disruptive gene alterations (e.g., missense variants) also lead to NSMI.
Table 3.
Selected CATSPER1 Pathogenic Variants Associated with NSMI
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DNA Nucleotide Change (Alias 1) | Predicted Protein Change | Reference Sequences |
---|
c.539dupT 2 | p.His182ProfsTer8 |
NM_053054.3
NP_444282.3
|
c.944_948dupATGGC (948-949insATGGC) 2 | p.Asp317MetfsTer20 |
Variants listed in the table have been provided by the authors. GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen.hgvs.org). See Quick Reference for an explanation of nomenclature.
- 1.
Variant designation that does not conform to current naming conventions
- 2.
Normal gene product. CATSPER1 protein is a 780-amino acid calcium channel that most closely resembles a single six-transmembrane-spanning repeat of the voltage-dependent calcium channel four-repeat structure. CATSPER is vital to cAMP-mediated calcium influx, sperm motility, and fertilization [Ren et al 2001].
Abnormal gene product. Loss of CATSPER1 function is associated with disease. Sperm motility parameters are all markedly impaired in CatSper1-/- (knockout) mouse sperm as compared to wild-type sperm [Ren et al 2001].
STRC
Gene structure.
STRC is a 29-exon gene and has a transcript length of 5,515 bp (NM_153700.2). For a detailed summary of gene and protein information, see Table A, Gene.
Pathogenic variants. The only known pathogenic variants of STRC in individuals with DIS are contiguous deletions that also delete CATSPER2 [Avidan et al 2003, Zhang et al 2007] (see Table 4). Other pathogenic variants in STRC as associated with nonsyndromic hearing loss (see Deafness and Hereditary Hearing Loss Overview.)
Normal gene product. STRC protein is 1775 amino acids in length (NP_714544.1). It is expressed in the stereocilia hair-bundle of outer hair cells, the inner ear cells that amplify the initial stimulation [Verpy et al 2008]. A deletion of the contiguous genes CATSPER2 and STRC results in the DIS phenotype; intragenic variants in STRC result in autosomal recessive nonsyndromic hearing loss (ARNSHL) at the DFNB16 locus [Verpy et al 2001, Avidan et al 2003, Zhang et al 2007, Knijnenburg et al 2009].
Abnormal gene product. Reported pathogenic variants in STRC that cause DIS are homozygous deletions of the entire gene as part of contiguous-gene deletion that includes CATSPER2; deletion of STRC results in loss of its encoded protein, stereocilin.
Deletion of STRC, which encodes stereocilin, underlies the hearing loss in DIS. Pathogenic variants of only STRC result in ARNSHL at the DFNB16 locus [Verpy et al 2001]. This is supported by the generation of Strc-/- (knockout) mice that have a specific outer hair cell defect, while their inner hair cells appear unaffected [Verpy et al 2001]. Inactivation of Strc in mice leads to failure of the cochlear amplifier [Verpy et al 2008]. This murine phenotype is in agreement with the moderate-to-severe hearing loss usually observed in individuals with DFNB16 or DIS.