MYO5B-associated diseases: Novel liver-related variants and genotype-phenotype correlation.

Background & Aims: Biallelic pathogenic variants in MYO5B cause microvillus inclusion disease (MVID), or familial intrahepatic cholestasis (FIC). The reported FIC patients are scarce and so the genotype-phenotype correlation has not been fully characterised. This study aimed to report more MYO5B-associated FIC patients and correlate genotypes to phenotypes in more detail.

Methods: The phenotype and genetic data of 12 newly diagnosed MYO5B-associated (including 11 FIC) patients, as well as 118 previously reported patients with available genotypes, were summarised. Only patients with biallelic MYO5B variants were enrolled. Nonsense, frameshift, canonical splice sites, initiation codon loss, and single exon or multiexon deletion were defined as null MYO5B variants.

Results: Phenotypically, 50 were isolated MVID, 47 involved both liver and intestine (combined), and 33 were isolated FIC (9 persistent, 15 recurrent, 3 transient, and 6 un-sub-classified) patients. The severity of intestinal manifestation was positively correlated to an increased number of null variants (ρ = 0.299, P = .001). All FIC patients carried at least one non-null variant, and the severity of cholestasis was correlated to the presence of a null variant (ρ = 0.420, P = .029). The proportion of FIC patients (16/29, 55%) harbouring missense/in-frame variants affecting the non-motor regions of MYO5B was significantly higher than that of MVID (3/25, 12%, P = .001) and combined patients (3/31, 10%, P = .000). 10 of the 29 FIC patients harboured missense/in-frame variants at the IQ motifs comparing to none in the 56 MVID and combined patients (P = .000).

Conclusions: The phenotype of MYO5B deficiency was associated with MYO5B genotypes, the nullity or the domain affected.