Infants with Menkes disease who began copper treatment within the neonatal period had better survival than infants who began treatment later. To identify candidates for treatment, we exploited the copper dependence of dopamine-β-hydroxylase by measuring plasma catecholamine levels in infants at risk. Our results indicate that this approach has high sensitivity and specificity for diagnosing Menkes disease prospectively, including during its brief presymptomatic stage.
Copper is incorporated into dopamine-β-hydroxylase apoenzyme within the trans-Golgi compartment of noradrenergic neurons, a process mediated by ATP7A. In patients with congenital absence of dopamine-β-hydroxylase, the ratio of dihydroxyphenylacetic acid to dihydroxyphenylglycol is greater than 1000:1 and the ratio of dopamine to norepinephrine is approximately 50:1.18
Our results indicate that small but highly consistent elevations in both of these ratios are characteristic of Menkes disease.
We and others have reported isolated cases of Menkes disease in which early treatment with injected copper was associated with variable clinical success7–13
or with failure.9,28
On the basis of the correlations between molecular findings and clinical success presented here, we suggest that the response to early copper treatment depends on the ATP7A
genotype and that optimal outcomes occur only in patients with mutations that permit some residual copper transport. The normal neurodevelopmental outcomes in Patients 5 and 8 may reflect the combined effect of the correction of serum copper levels () and the capacity for residual copper-transport activity associated with IVS9,DS,+6T→G and G666R, respectively. We speculate that this activity was sufficient for delivery of copper across the blood–brain barrier.
Patient 4, who also had the G666R mutation, showed some delay in all neurodevelopmental spheres at 36 months of age (), although his clinical outcome was better than that of most members of this cohort and better than that of his maternal uncle, who received a diagnosis later. Although compliance with the experimental treatment appeared to be excellent, this infant entered the trial at 22 days of age, 8 to 17 days later than all other participants. This later initiation of treatment may explain the less successful treatment outcome.
We found no evidence for residual copper transport in patients with ATP7A
deletions that disrupt the translational reading frame, and the nine infants with Menkes disease who had these mutations did not achieve normal neurodevelopment, despite early treatment. However, these patients had better survival and a lower incidence of clinical seizures (two of nine infants, or 22%) than would be expected among those with untreated Menkes disease,4
perhaps as a result of their access to early diagnosis and treatment. The mechanisms underlying these improvements in patients with complete loss-of-function mutations remain unclear.
More than 3 years of copper-replacement therapy for patients with Menkes disease may not be necessary or desirable. We chose a 3-year treatment period on the basis of the expected nephrotoxicity of the study drug and the knowledge that brain myelination is typically completed by 24 months of age. We found evidence of renal tubular damage associated with copper treatment in all patients tested, although this damage appears to be reversible. For example, in Patient 5, the urinary concentration of β2-microglobulin reached 28.0 mg per liter (2373.0 nmol per liter) during treatment and declined to a normal level of 0.1 mg per liter (8.4 nmol per liter) 3 years after cessation of treatment.
Patients who completed the trial have shown no declines in neurologic or cognitive skills after termination of treatment. This is also the case for a patient we previously reported on12
who remains alive and well at the age of 13 years with no neurologic or cognitive impairments 10 years after cessation of treatment.
The enhanced survival and improved outcomes associated with early diagnosis have implications regarding screening newborns for Menkes disease by measuring the blood levels of one or more of the neurochemicals measured in our study. These compounds can be detected by high-throughput tandem mass spectrometry techniques,29,30
and evaluation of their levels in dried blood spots obtained from newborns at risk could assess the suitability of this approach for mass screening.
Advances in understanding the clinical, biochemical, and molecular aspects of Menkes disease have outpaced progress in the design of therapies effective for all patients with this diagnosis. Since optimal response to copper-injection treatment appears to occur only in patients who are identified in the newborn period and whose mutations permit residual copper-transport activity, additional approaches, including ATP7A gene transfer, are relevant future considerations.