Clinical Characteristics
Table 1 lists the clinical characteristics of the six AMN patients. Median age at onset of neurological symptoms was 29.8 years and ranged 21–38 years. All 6 patients are men. Duration of follow-up from onset ranged between 47 months to 128 months. The mother of patient 6 with obvious skin pigmentation and we confirm her disease by gene sequencing. The other two patients (patient 2 and 4) with suspected positive family history: the maternal cousin of patient 2 had suffered from limb weakness and cutaneous pigmentation, but he refused further check. The maternal uncle of patient 4 had symptom of ambulation dysfunction, unfortunately we could not identify his disease because of his reject.
Initial neurological symptoms included stiffness or weakness of the legs in five patients and backache in one left (patient 4). Four patients without cerebral involvement, other two patients incorporated with abnormal head MRI. Among them, two patients (patients 1, 4) were initially suspected as hereditary spastic paraplegia because of adolescent onset with spastic paraparesis, and other two patients (patients 2, 3) were initially misdiagnosed as subacute combined degeneration due to damage of dorsolateral funiculus and peripheral nerve.
Five patients had hyperpigmentation in lips, areolae, gums even the entire body skin (FIG. 1), and the plasma of ACTH concentration of these patients was elevated obviously. After patient 1 and patient 3 had received hydrocortisone therapy regularly, the level of plasma of ACTH returned to normal after 2-4 weeks. Moreover, the symptoms of skin pigmentation and fatigue also significantly improved. Five patients complained decreased libido and erectile dysfunction, but the levels of testosterone were in the normal range. In our cohort, all patients with scanty scalp hair, patient 6 developed male type balding (FIG. 2).
On neurologic examination, all patients presented spasticity and paresis, as well as increased tendon reflexes with Babinski sign. Meanwhile, five patients displayed prominent dorsal column dysfunction. Five patients had urinary disturbance (retention, urgency or incontinence). Patient 6 demonstrated personality change, memory impairment and dysarthria at the age of 39. Although there were lesions in the brain, patient 1 had no obvious personality change or memory impairment. Nerve conduction studies showed abnormal in 4 of 5 tested patients. Three patients with bilateral peroneal velocity abnormal, the other one with peroneal velocity and amplitude decreased. Somatosensory evoked potential experiments proved that 4 monitored patients had central conduction abnormalities.
Neuroimaging
All patients underwent brain and spinal MRI testing. As a result, spinal MRI scans showed diffuse cord atrophy in all cases, especially patient 2 and patient 6 (FIG. 3). Interestingly, patient 1 didn’t have any obvious mood or memory disturbance until the follow-up date, but the lesion of splenium of corpus callosum have become more and more visible during the past 6 years (FIG. 4), which indicates that the initial lesions usually relate to the splenium of the corpus callosum and subsequently spread to the adjacent white matter of the parieto-occipital lobe. The brain MRI of patient 6 revealed extensive intracranial lesions, including splenium of corpus callosum, bilateral symmetrical temporo-parietal-occipital white matter, bilateral corticospinal tract, and bilateral dentate nuclei of cerebellar (FIG. 5).
Biochemical
Table 2 lists the plasma VLCFAs levels of five tested patients. While patient 5 refused to undergo this check after genetic diagnosis. It is revealed that plasma levels of VLCFA, and the proportions of C24:0/C22:0 and C26:0/C22:0 were elevated in all tested patients. Although patient 1 received treatment with Lorenzo’s oil regularly, the plasma levels of C26:0, especially the C24:0/C22:0 and C26:0/C22:0 ratios were still above normal range.
Mutational analysis
To analyze mutational features, five distinct mutations of the ABCD1 sequence were confirmed (Table 3). Among these five different mutations, four are missense, and one is a novel frameshift mutation. As to the missense counterparts, three mutations are identified in the nucleotide binding domains (NBD), and another one is located in the transmembrane domain. The ALD database (see http://www.x-ald.nl/) actually have disclosed these 4 mutations, which are not only associated with AMN but also with the phenotype of childhood cerebral ALD, adolescent cerebral ALD, adult cerebral ALD, or the asymptomatic patients12-15. In this study, one novel frameshift mutation (c.1843dup) was identified in our cohort. As aforementioned, the ABCD1 gene coding for a protein of 745 amino acids (named ALDP), is formed from 10 exons16. Here the novel frameshift mutation located in exon 8, which leaded to the protein early terminated at exon 9 (FIG. 6).