Differences in ATP7A gene expression underlie intrafamilial variability in Menkes disease/occipital horn syndrome

Background: Pronounced intrafamilial variability is unusual in Menkes disease and its variants. We report two unrelated families featuring affected members with unusually disparate clinical and biochemical phenotypes and explore the underlying molecular mechanisms. Methods: We measured biochemical markers of impaired copper transport in five patients from two unrelated families and used RNase protection, quantitative reverse transcription (RT)-PCR, Western blot analysis and yeast complementation studies to characterise two ATP7A missense mutations, A1362D and S637L. Results: In two brothers (family A) with A1362D, RNase protection and Western blot analyses revealed higher amounts of ATP7A transcript and protein in the older, mildly affected patient, who also had a higher plasma copper level and lower cerebrospinal fluid dihydroxyphenylalanine : dihydroxyphenylglycol ratio. These findings indicate greater gastrointestinal absorption of copper and higher activity of dopamine-β-hydroxylase, a copper-dependent enzyme, respectively. In family B, three males with a missense mutation (S637L) in an exon 8 splicing enhancer showed equally reduced amounts of ATP7A transcript and protein by quantitative RT-PCR and western blot analysis, respectively, despite a more severe phenotype in the youngest. This patient’s medical history was notable for cardiac arrest as a neonate, to which we attribute his more severe neurodevelopmental outcome. Conclusions: These families illustrate that genetic and non-genetic mechanisms may underlie intrafamilial variability in Menkes disease and its variants.