Categories: Mortality / aging (incl. embryonic lethal)

Single-gene trait/disorder: yes

Mode of inheritance: Autosomal dominant + recessive lethal

Disease-related: yes

Key variant known: yes

Year key variant first reported: 2026

Species-specific name: Recessive lethality and/or reduced male fertility / reduced insemination success

Mapping: Steensma et al. (2026) identified 10 haplotypes with homozygous deficiency by analyzing 70K SNP data from over 8000 Friesian horses. The authors identified candidate haplotypes: FH1-FH10 on chromosomes 1, 4 (3 haplotypes), 5, 6, 9, 14, 18 and 23 (OMIA:003063-9796 : Haplotype with homozygous deficiency, FH1-FH10) and identified 4 causal variants for 6 of these haplotypes, including the variant listed below. 

Molecular basis: Whole genome sequencing of sires that were carriers for the FH10 haplotype identied a large deletion on chromosome 23 encompassing SLC28A3-like and SPATA31D-like genes and ncRNAs: NC_009166.3:g.5958862del356kb, omia.variant:1913 (Steensma et al. 2026).

Clinical features: Steensma et al. (2026) reported that carriers for omia.variant:1913 had increased abnormal sperm head shape and no homozygotes were observed for this variant in carrier by carrier matings.

Breed: Friesian (Horse) (VBO_0000969).
Breeds in which the phene or likely causal variants have been documented. If a likely causal variant has been documented, see variant-specific breed information in the variant table. (Breed information may be incomplete).