Metachromatic leukodystrophy (MLD) is a rare autosomal recessive lysosomal storage disease caused by deficient activity of arylsulfatase A, leading to sulfatide accumulation in nervous system cells. Little is known about disease natural history. A qualitative analysis was performed using transcripts of in-depth telephone interviews with 32 parents of patients with MLD (16 late-infantile-onset; 16 juvenile-onset). Mean patient age at interview was 7.6 and 20.7 years for the late-infantile- and juvenile-onset groups, respectively. For patients with late-infantile-onset MLD, mean reported age at first symptom and diagnosis were 1.5 and 2.6 years, respectively. Among the late-infantile onset group, 12 caregivers (75%) reported impairments in gross motor functioning as the first symptom, most commonly difficulties learning to walk (69% did not learn to walk independently). This form was characterized by rapid decline (mean time from first symptom to first functional loss, 1.0 year). In the juvenile-onset group, mean age at first symptom and diagnosis was 8.7 and 11.6 years, respectively; most frequently reported initial symptoms were cognitive (56%) or behavioural (44%), with subsequent deteriorations in physical ability. Decline was generally less aggressive in this form than late-infantile-onset MLD (mean time from first symptom to first functional loss, 6.1 years). At interview, no patients with late-infantile-onset MLD were able to walk independently; five patients with juvenile-onset MLD could walk independently, although only one had little/no physical impairment. These interviews confirm distinctions between late-infantile and juvenile-onset MLD, with the former characterized by motor issues and rapid decline, and the latter by mixed cognitive, behavioural and motor issues and slower progression. Both forms had delayed diagnosis; increased disease awareness might reduce these delays. Although the recollections of caregivers may not provide exact timelines for progression, the findings were consistent with published descriptions and further our understanding of MLD.
