Faculty Bibliography

The leukodystrophies comprise an ever-expanding group of rare central nervous system disorders with defined clinical, pathological, and genetic characteristics. The broader term, leukoencephalopathy, is applied to all brain white matter diseases, whether their molecular cause is known. Magnetic resonance imaging has helped to elucidate new forms of leukodystrophy as well as to permit longitudinal studies of disease progression. The white matter abnormality may appear similar in different forms of leukodystrophy so that in most cases, further studies such as magnetic resonance spectroscopy, tissue biopsies, enzyme studies, and molecular DNA analyses are needed to pinpoint the specific diagnosis. The primary inherited leukoencephalopathies include dysmyelinating, hypomyelinative, and vacuolating forms. Metabolic and vascular causes account for most of the secondary forms, but other inherited syndromes are recognized that have their onset in childhood or adult life and are characterized by distinctive clinical and neuropathologic features. This review discusses some of the mechanisms that have been proposed to explain deficiencies of myelin and the molecular genetic bases underlying these disorders

Canavan disease (CD), an autosomal recessive neurodegenerative disorder, is caused by mutations in the aspartoacylase (ASPA) gene. In the present study, the ASPA gene was analyzed in 24 non-Jewish patients with CD from 23 unrelated families. Within this cohort, we found three large novel deletions of approximate 92, 56, and 12.13 kb in length, using both self-ligation of restriction endonuclease-digested DNA fragments with long-distance inverse PCR and multiplex dosage quantitative PCR analysis of genomic DNA. The 92 kb large deletion results in complete absence of the ASPA gene in one homozygous and one compound heterozygous patient, respectively. The 56 kb large deletion causes absence of the majority of the ASPA gene except for exon 1 alone in a compound heterozygous patient. The 12.13 kb deletion involves deletion of the ASPA gene from intron 3 to intron 5 including exons 4 and 5 (I3 to E4E5I5) in a compound heterozygous patient. Patients with the three large deletions clinically manifested severe symptoms at birth, including seizures. Our study showed that the combined use of long-distance inverse PCR and multiplex dosage quantitative PCR analysis of genomic DNA is a helpful and rapid technique to search for large deletions, particularly for detection of large deletions in compound heterozygous patients

We describe two sisters with a mild-onset variant of Canavan's disease who presented at age 50 and 19 months with developmental delay but without macrocephaly, hypotonia, spasticity, or seizures. Remarkably, both patients had age-appropriate head control, gross motor development, and muscle tone. There were very mild deficits in fine motor skills, coordination, and gait. Both sisters had a history of strabismus, but otherwise vision was normal. The older child showed evidence of mild cognitive and social impairment, whereas language and behavior were normal for age in the infant. Both patients were found to be compound heterozygotes for C914A (A305E) and G212A (R71H) mutations in ASPA. Like all other known ASPA mutations, this previously unknown G212A mutation appears to have low absolute enzyme activity. Nevertheless, it is associated in these patients with an extremely benign phenotype that is highly atypical of Canavan's disease. Biochemical and clinical data were evaluated using a generalized linear mixed model generated from 25 other subjects with Canavan's disease. There were statistically significant differences in brain chemistry and clinical evaluations, supporting a distinct variant of Canavan's disease. Future studies of ASPA enzyme structure and gene regulation in these subjects could lead to a better understanding of Canavan's pathophysiology and improvements in ASPA gene therapy Ann Neurol 2006;59:428-431

OBJECTIVE: To determine the clinical consequences of the PMP22 point mutation, T118M, which has been previously considered to either cause an autosomal recessive form of Charcot-Marie-Tooth (CMT) disease or be a benign polymorphism. METHODS: We analyzed patients from five separate kindreds and characterized their peripheral nerve function by clinical and electrophysiological methods. RESULTS: All heterozygous patients had clinical and/or electrophysiological features of a neuropathy similar to hereditary neuropathy with liability to pressure palsies (HNPPs). The homozygous patient had a severe axonal neuropathy without features of demyelination. INTERPRETATION: These findings suggest that T118M PMP22 retains some normal PMP22 activity, allowing the formation of compact myelin and normal nerve conduction velocities in the homozygous state. Taken together, these findings suggest that T118M is a pathogenic mutation causing a dominantly inherited form of CMT by a partial loss of PMP22 function.

Mutations in the proteolipid protein 1 (PLP1) gene cause the X-linked dysmyelinating diseases Pelizaeus-Merzbacher disease (PMD) and spastic paraplegia 2 (SPG2). We examined the severity of the following mutations that were suspected of affecting levels of PLP1 and DM20 RNA, the alternatively spliced products of PLP1: c.453G>A, c.453G>T, c.453G>C, c.453+2T>C, c.453+4A>G, c.347C>A, and c.453+28_+46del (the old nomenclature did not include the methionine codon: G450A, G450T, G450C, IVS3+2T>C, IVS3+4A>G, C344A, and IVS3+28-+46del). These mutations were evaluated by information theory-based analysis and compared with mRNA expression of the alternatively spliced products. The results are discussed relative to the clinical severity of disease. We conclude that the observed PLP1 and DM20 splicing patterns correlated well with predictions of information theory-based analysis, and that the relative strength of the PLP1 and DM20 donor splice sites plays an important role in PLP1 alternative splicing