Faculty Bibliography

Hereditary spastic paraplegia (HSP) is a degenerative disorder of the motor system, defined by progressive weakness and spasticity of the lower limbs. HSP may be inherited as an autosomal dominant (AD), autosomal recessive, or an X-linked trait. AD HSP is genetically heterogeneous, and three loci have been identified so far: SPG3 maps to chromosome 14q, SPG4 to 2p, and SPG4a to 15q. We have undertaken linkage analysis with 21 uncomplicated AD families to the three AD HSP loci. We report significant linkage for three of our families to the SPG4 locus and exclude several families by multipoint linkage. We used linkage information from several different research teams to evaluate the statistical probability of linkage to the SPG4 locus for uncomplicated AD HSP families and established the critical LOD-score value necessary for confirmation of linkage to the SPG4 locus from Bayesian statistics. In addition, we calculated the empirical P-values for the LOD scores obtained with all families with computer simulation methods. Power to detect significant linkage, as well as type I error probabilities, were evaluated. This combined analytical approach permitted conclusive linkage analyses on small to medium-size families, under the restrictions of genetic heterogeneity

Krabbe's disease or globoid cell leukodystrophy is a rare demyelinating disorder of the central and peripheral nervous systems, the diagnosis of which is based on clinical findings and the determination of low to absent functional activity of the enzyme beta-galactocerebrosidase. We report the presentation of late-onset Krabbe's disease in 2 siblings, a 17-year-old boy and his 16-year-old sister, both with marked deficiency of the enzyme beta-galactocerebrosidase. Only the older sibling manifested clinical signs and symptoms of the disease, while the younger sister remained asymptomatic to date. Molecular analyses disclosed the presence in this family of two novel single point mutations within the gene for galactocerebrosidase

Globoid-cell leukodystrophy (GLD) is an autosomal recessive inherited disorder caused by the deficiency of galactocerebrosidase, the lysosomal enzyme responsible for the degradation of the myelin glycolipid galactocerebroside. Although the most common form of the disease is the classical infantile form (Krabbe disease), later-onset forms also have been described. We have analyzed the galactocerebrosidase gene in 17 patients (nine families) with late-onset GLD and in 1 patient with classical Krabbe disease. Half of the patients were heterozygous for the large gene deletion associated with the 502C-->T polymorphism, the most common mutation in infantile patients. Several novel mutations that result in deficient galactocerebrosidase activity were also identified in these patients. They include the missense mutations R63H, G95S, M101L, G268S, Y298C, and I234T; the nonsense mutation S7X; a one-base deletion (805delG); a mutation that interferes with the splicing of intron 1; and a 34-nt insertion in the RNA, caused by the aberrant splicing of intron 6. All of these genetic defects are clustered in the first 10 exons of the galactocerebrosidase gene and therefore affect the 50-kD subunit of the mature enzyme. Studies on the distribution and enzymatic activity of the polymorphic alleles 1637T/C (I546/T546) provided support for previous data that had indicated the existence of two galactocerebrosidase forms with different catalytic activities in the general population. Our data also indicate that the mutations occur preferentially in the 'low activity' 1637C allele

Antibodies against the myelin glycolipid galactosylceramide are widely used to study the distribution and function of this molecule. However, anti-galactosylceramide antibodies are not monospecific and have been shown to recognize epitopes carried not only by other glycolipids, but also by proteins. Using expression cloning we have identified a human kidney cDNA which induces a cell-surface protein recognized by the anti-galactosylceramide monoclonal antibody R-mab. These findings further support the idea that cross-reactive proteins may mediate some of the biological effects of the anti galactosylceramide antibodies

We report three patients with severe pontocerebellar atrophy (PCA) associated with a variable degree of cerebral atrophy. The clinical features consisted of progressive microcephaly, central hypotonia, visual impairment, abnormal eye movements and delayed psychomotor development. These are similar but not identical to the features of pontocerebellar hypoplasia type 2 described by Barth. The picture also differs from the classical form of autosomal dominant olivopontocerebellar atrophy. While in two patients the disease seemed to be genetic with highly suspicious autosomal recessive inheritance, the etiology in the third patient was probably nongenetic. We suggest that PCA is a morphologic entity with distinct radiologic features but variable clinical, pathophysiologic and etiologic backgrounds

The case of a 6-year-old boy who developed childhood disintegrative disorder (Heller syndrome) at the age of 4 years is presented, and specifics of the neurologic evaluation are detailed. A table is provided suggesting the complete neurologic work-up with the potential findings for children presenting with signs and symptoms of deterioration. A hypothesis for the aetiology of Heller syndrome proposes that predisposing genetic factors when combined with an environmental stress result in the deposition of amyloid and the disruption of synaptic transmission during the deterioration period. Speculation that the deterioration may be self-limited by activation of an immune response is based upon earlier findings that interleukin 1 has been shown to be involved in the breakdown of amyloid precursor protein in humans

Late-onset GM2 gangliosidosis is a variant form of Tay-Sachs disease characterized by onset of symptoms and signs in adolescence or in early adult life. The deficiency of beta-hexosaminidase A (Hex A) in this form of GM2 gangliosidosis has been invariably associated with the presence of the Gly269-->Ser substitution in the alpha-chain. We found two siblings of Ashkenazi Jewish descent diagnosed with late-onset GM2 gangliosidosis who were negative for the Gly269-->Ser mutation. Analysis of the HEXA gene showed that they were compound heterozygotes for the functionally silent 4-bp insertion in exon 11, typical of the infantile form of the disease and for a novel mutation, T538-->C, resulting in the missense Tyr180-->His. Expression studies in COS-7 cells suggested that the effect of this mutation was to decrease the stability of the alpha-chain at physiologic temperatures and therefore to indirectly affect the formation of mature Hex A

Three children are reported with mitochondrial encephalomyopathy who presented with autonomic dysfunction. Autonomic dysfunction included gastrointestinal dysmotility, apnea, cardiac arrhythmias, decreased lacrimation, supersensitivity to metacholine, altered sweating, and postural hypotension. These patients illustrate that in some mitochondrial encephalomyopathies autonomic features may be prominent and can mimic the clinical features associated with hereditary sensory and autonomic neuropathies