Phenotype assignment in symptomatic female carriers of X-linked adrenoleukodystrophy

Abstract

Approximately 20% of female heterozygotes of X-linked adrenoleukodystrophy (X-ALD) develop neurological symptoms clinically resembling those of adrenomyeloneuropathy in men. However, only very few studies have systematically investigated the extent and distribution of nervous and endocrine system involvement in femal carriers of X-ALD. To define the phenotype in symptomatic female carriers of X-ALD we performed a prospective study including eight symptomatic women who were followed for a mean period of 3.4±1.8 years (range 1–6) using standardized clinical examination protocols, magnetic resonance imaging and spectroscopy, evoked potential studies including visual, brainstem auditory, somatosensory and magnetic evoked potentials, neurographic recordings and endocrine studies. Spastic paraparesis and decreased vibration sense in the lower extremities were the most frequent clinical findings. Slightly hyperintense symmetric parieto-occipital white matter lesions on magnetic resonance imaging were detectable in two of seven cases, and the N-acetylaspartate/choline ratios on magnetic resonance spectroscopy were decreased in three of seven patients. P40 latencies were abnormal in all patients, and central motor conduction times to the lower extremities in seven of eight patients. Prolonged latencies of brainstem auditory evoked potential waves III–V or interpeak latencies of waves I–III, I–V and III–V were detectable in all patients. The degree of walking impairment was positively correlated with the duration of clinical disease (r=0.58, P < 0.05) and inversely correlated with the N-acetylaspartate/choline ratios (r=0.85; P < 0.05). Neurographic recordings revealed only subtle abnormalities, suggesting that nervous system involvement in symptomatic female carriers of X-ALD is confined mainly to the central nervous system. No evidence of adrenal insufficiency was detected in any of the patients.