Differences in ATP7A gene expression underlie intra-familial variability in Menkes disease/occipital horn syndrome

Anthony Donsante ¹, Jingrong Tang ¹, Sarah C Godwin ¹, Courtney S Holmes ², David S Goldstein ², Alexander Bassuk ³ and Stephen G. Kaler ^1*

¹ Unit on Pediatric Genetics, NICHD, NIH, United States
² Clinical Neurocardiology Section, NINDS/NIH, United States
³ Depts of Pediatrics & Neurology, Northwestern University School of Medicine, United States

^* To whom correspondence should be addressed. E-mail: kalers{at}mail.nih.gov.

Accepted 27 April 2007

Abstract

Background: Pronounced intra-familial 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 molecular underpinnings.

Methods: We measured biochemical markers of impaired copper transport in 5 patients from two unrelated families, and used RNase protection, quantitative RT-PCR, western blot analysis, and yeast complementation studies to characterize 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--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 analysis, respectively, despite a more severe phenotype in the youngest. His 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 intra-familial variability in Menkes disease and its variants.

Keywords: Gene expression, Menkes disease, Occipital Horn Syndrome, Residual copper transport

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