Remarkably, there is no difference in sequences between calf and dam with respect to exon 39 of ABCA12 gene. They are similar to the normal sequence in the genome database (chromosome 2, ARS-UCD2.0) indicating that the said SNP (NM_001191294.2:g.103030489T>C) (H1935R) has no role in the present condition. Moreover, our results align with a study by Rourke et al. (2017), which reported that the known H1935R mutation was not responsible for the harlequin ichthyosis in Poll Hereford and shorthorn calves. This finding led us to conclude that allelic heterogeneity plays a crucial role in the existence of the disease.
Further, Wolley et al. (2019) reported another missense variation in the ABCA12 (NM_001191294.2:c.6776T>C) as the cause for harlequin ichthyosis in shorthorn animals with the estimated gene frequency was 3.8% in the population. Jacinto et al. (2021) found that the homozygous frameshift 1 bp insertion of FA2H gene is responsible for the ichthyosis congenita in Italian Chianna cattle and estimated gene frequency of 7.5%. Across cattle breeds, seven different genes are identified as responsible for harlequin ichthyosis. A missense mutation in the ABCA12 gene is responsible for lamellar ichthiosis type 2 in humans (Lefevre et al. 2003). However, nonsense, frameshift and some rare missense mutation are causal reasons for severe ichthyosis (Kelsell et al. 2005; Thomas et al. 2006; Akiyama et al. 2006; Thomas et al. 2008). To the best of our knowledge, Ichthyosis condition is not reported in Bos indicus breed to date.
Despite, the advancements in understanding of Harlequin Ichthyosis, an unusual genetic disorder, it's crucial to acknowledge that these conditions remain incurable in both animals and humans. Consequently, there is a growing need for greater awareness among practitioners. This is particularly essential for implementing proper breeding programs, and the identification of carriers in both males and females may prove instrumental in restricting the prevalence of the disease in the field.