Disorders of Copper Transport

我们的转化研究侧重于铜代谢障碍的诊断、治疗和理解，这是最近扩大的一系列影响中枢和周围神经系统不同组成部分的人类疾病。获得和遗传形式的异常铜稳态与神经功能障碍有关。门克斯病（MD）是一种典型的铜转运缺陷遗传综合征，其特征是脑铜含量低、婴儿神经退行性变和过早死亡。MD是由x链铜转运体基因ATP7A突变引起的。枕角综合征（OHS）是一种较轻的等位基因变异，与ATP7A剪接突变泄漏有关，其中自主神经功能障碍占主导地位。最近，我们发现了几个运动神经元疾病家族，类似于腓骨肌萎缩侧索硬化症和肌萎缩性侧索硬化症，这些疾病是由ATP7A羧基一半的几个新的错义突变引起的。这些都是轻微的功能缺失，似乎会影响ATP7A的细胞内运输。因此，ATP7A突变的表型谱已经扩大；这些新的等位基因变异的发现表明，ATP7A在运动神经元的维持和功能中起着以前未被认识到的作用。

Our translational research focuses on the diagnosis, treatment, and understanding of copper metabolism disorders, a recently expanded collection of human diseases that impact varied components of the central and peripheral nervous systems. Acquired as well as inherited forms of abnormal copper homeostasis are implicated in neurologic dysfunction. Menkes disease (MD), a prototypical genetic syndrome of defective copper transport, is characterized by low brain copper, infantile neurodegeneration, and premature death. MD is caused by mutations in an X-linked copper transporter gene, ATP7A. The occipital horn syndrome (OHS) is a milder allelic variant associated with leaky ATP7A splice junction mutations, in which autonomic dysfunction predominates. Recently, we identified several families with motor neuron disease resembling Charcot-Marie-Tooth disease and amyotrophic lateral sclerosis, that are caused by several novel missense mutations in the carboxyl half of ATP7A. These are mild loss-of- function defects that appear to affect intracellular trafficking of ATP7A. Thus, the phenotypic spectrum of ATP7A mutations has expanded; discovery of these new allelic variants indicates a previously unappreciated role for the ATP7A in motor neuron maintenance and function. Current treatment for MD is limited to subcutaneous copper injections and is effective in patients with mutant alleles that do not completely abrogate ATP7A function, and who are identified near birth (N Engl J Med 2008;358:605-614). For patients with complete loss-of-function mutations, however, copper delivered peripherally does not cross the blood-brain barrier efficiently, and alternative treatment approaches are needed. In our recent exploration of treatment alternatives, we rescued a mouse model of severe Menkes disease using combination brain-directed therapies: recombinant adeno-associated virus serotype 5 (AAV5) vector expressing a reduced size human ATP7A, plus copper. Neither treatment alone was effective, but combination therapy dramatically shifted the Kaplan-Meier survival curve, with 5 of 16 (31%) combination-treated mutants surviving beyond 110 days of age (p<0.0002). Combination-treated mo-br mice weighed more than untreated mo-br mice (5.2 g vs. 4.2 g at 9 days of age, p<0.02) and less than wild type controls (11.9 g vs. 15.1 grams at 27 days of age, p<0.01). The combination-treated survivors appear healthy, active, and fertile. The mechanisms underlying this pronounced synergistic effect help to illuminate the normal processes of copper transport in brain, and the role of ATP7A in neuronal and neuroglial cells. In addition, this advance may hold future clinical implications for Menkes disease patients with severe ATP7A mutations, as well as for patients with ATP7A-related motor neuron disease. The synthetic amino acid L-threo-3,4-dihydroxyphenylserine (L-DOPS) is highly effective in reversing neurogenic orthostatic hypotension and correcting neurochemical abnormalities in patients with autosomal recessive congenital absence of dopamine-beta-hydroxylase (DBH). L-DOPS is metabolized by the enzyme DOPA decarboxylase to produce norepinephrine, thus bypassing the DBH enzymatic defect. Individuals occipital horn syndrome (OHS), have partial deficiency of DBH, which is copper-dependent, and show distinctive neurochemical abnormalities and often symptoms of dysautonomia, such as syncope, dizziness, orthostatic hypotension, abnormal sinoatrial conduction, nocturnal bradycardia, and bowel or bladder dysfunction. As in patients with congenital absence of DBH, these problems in autonomic nervous system function seem potentially responsive to restoration of normal neurochemical levels. We hypothesize that L-DOPS treatment in OHS patients with dysautonomia will correct or improve blood neurochemical levels, and produce concurrent symptomatic improvement. A recently IRB-approved pilot study will test this hypothesis in six patients with dysautonomic symptoms, by providing L-DOPS treatment (5mg/kg/d po qd) and assessing the neurochemical response (in-hospital plasma catechol levels) and the longer-term effect on symptoms (out-of-hospital autonomic symptom questionnaire completed weekly by subject and/or parent), during an eight-week period while receiving the study drug.