adld leukodystrophyhypomyelinating leukodystrophymetachromatic leukodystrophy symptomsmitochondrial leukodystrophycongenital leukodystrophygloboid leukodystrophyleukodystrophy diagnosisinfantile leukodystrophyleukodystrophy prognosisalexander leukodystrophymetabolic leukodystrophycerebral leukodystrophy