Isolated ocular disease is associated with decreased mucolipin-1 channel conductance

To evaluate a 15-year-old boy with MLIV (mucolipidosis type IV) and clinical abnormalities restricted to the eye who also had achlorhydria with elevated blood gastrin levels.

In addition to a detailed neuro-ophthalmic and electrophysiological assessment, his mutant mucolipin-1 was experimentally expressed in liposomes and its channel properties studied in vitro.

The patient was a compound heterzygote for c.920delT and c.1615delG. Detailed neuro-ophthalmic examination including electroretinography showed him to have a typical retinal dystrophy predominantly affecting rod and bipolar cell function. In vitro expression of MCOLN1 in liposomes showed that the c.1615delG mutated channel had significantly reduced conductance compared with wild-type mucolipin-1, whereas the inhibitory effect of low pH and amiloride remained intact.

These findings suggest that reduced channel conductance is relatively well tolerated by the brain during development, whereas retinal cells and stomach parietal cells require normal protein function. MLIV should be considered in patients with retinal dystrophy of unknown cause and screened for using blood gastrin levels.