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Inactivating mutations of the gene encoding parkin are responsible for autosomal recessive juvenile parkinsonism (AR-JP). However, little information is known about the function and distribution of parkin. We generated antibodies to two different peptides of parkin. By Western blot analysis and immunohistochemistry, we found that parkin is a 50-kd protein that is expressed in neuronal processes and cytoplasm of selected neurons in the basal ganglia, midbrain, cerebellum, and cerebral cortex. Unlike ubiquitin and alpha-synuclein, parkin labeling was not found in Lewy bodies of four sporadic Parkinson disease brains. Parkin was colocalized with actin filaments but not with microtubules in COS1 kidney cells and nerve growth factor-induced PC12 neurons. These results point to the importance of the cytoskeleton and associated proteins in neurodegeneration.

Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of a CAG trinucleotide repeat located in the coding region of the human SCA2 gene. The SCA2 gene product, ataxin-2, is a basic protein with two domains (Sm1 and Sm2) implicated in RNA splicing and protein interaction. However, the wild-type function of ataxin-2 is yet to be determined. To help clarify the function of ataxin-2, we produced antibodies to three antigenic peptides of ataxin-2 and analyzed the expression pattern of ataxin-2 in normal and SCA2 adult brains and cerebellum at different developmental stages. These studies revealed that (1) both wild-type and mutant forms of ataxin-2 were synthesized; (2) the wild-type ataxin-2 was localized in the cytoplasm in specific neuronal groups with strong labeling of Purkinje cells; (3) the level of ataxin-2 increased with age in Purkinje cells of normal individuals; and (4) ataxin-2-like immunoreactivity in SCA2 brain tissues was more intense than in normal brain tissues, and intranuclear ubiquitinated inclusions were not seen in SCA2 brain tissues.

Mutations in the neurofibromatosis 2 (NF2) tumor suppressor gene on chromosome 22q12 cause a clinically variable autosomal dominant syndrome characterized by bilateral vestibular schwannomas (VSs), other nervous system tumors, and early onset lenticular cataracts. We studied three pairs of monozygotic (MZ) twins with NF2, all with bilateral VSs, to separate genetic from nongenetic causes of clinical variability. The evaluation included gadolinium-enhanced high-resolution magnetic resonance imaging of the head and spine, neuro-ophthalmic examination with slit lamp, physical examination, and zygosity testing with microsatellite markers. Each MZ pair was concordant for general phenotypic subtype (mild or severe) and often for the affected organ systems. However, the MZ pairs were discordant for some features of disease presentation or progression. For example, all three pairs were discordant for presence or type of associated cranial tumors. We hypothesize that phenotypic differences between NF2 MZ twins are at least partly due to stochastic processes, such as the loss of the second NF2 allele or alleles of other genes.

Neurofibromatosis type 2 (NF2) is a monogenic dominantly inherited disease that predisposes to the development of tumors of the nervous system, particularly meningiomas and schwannomas. The gene which, when altered, causes NF2, is localized on chromosome 22 and has recently been identified. The NF2 gene is also the site of somatic mutation in tumors, suggesting that it might have a tumor suppressor activity. We here report a screening method for the detection of point mutations in NF2 which takes advantage of denaturing gradient gel electrophoresis (DGGE). This method efficiently screens 95% of the coding sequence and 90% of intron/exon junctions. When applied to 91 unrelated NF2 patients, it enabled the identification of 32 germ-line mutations. Since mutations are found in only one third of the patients, it is expected that mutations or deletions affecting the promoter and/or intronic regions of the NF2 gene occur frequently. The characterized mutations are preferentially located within the 5' half of the gene. Most of them are predicted to lead to the synthesis of a truncated protein. A search for genotype/phenotype correlations showed that, at least in this series of patients, mild manifestations of the disease were associated with mutations which preserve the C-terminal end of the protein.

Alzheimer disease (AD) is a devastating neurodegenerative disease leading to global dementia. In addition to sporadic forms of AD, familial forms (FAD) have been recognized. Mutations in the amyloid precursor protein (APP) gene on chromosome (CHR) 21 have been shown to cause early-onset AD in a small number of pedigrees. Recently, linkage to markers on CHR 14 has been established in several early-onset FAD pedigrees. We now report lod scores for CHR 14 markers in two large early-onset FAD pedigrees. Pairwise linkage analysis suggested that in these pedigrees the mutation is tightly linked to the loci D14S43 and D14S53. However, assumptions regarding marker allele frequencies had a major and often unpredictable effect on calculated lod scores. Therefore, caution needs to be exercised when single pedigrees are analyzed with marker allele frequencies determined from the literature or from a pool of spouses.

Ring chromosome 21 results in deletions of chromosome 21. We report on a cytogenetic and molecular analysis of a 4-generation family segregating a stable ring chromosome 21 in 4 relatives. To investigate the molecular structure of the ring chromosome, we have analyzed the DNAs of the transmitted ring in a mother and her daughter. The daughter presented at the age of 2 years with severe growth retardation and microcephaly, whereas her mother had microcephaly but normal intelligence. High resolution chromosome analysis of both cases showed the ring chromosome to be r(21)(p13q22) resulting in deletions of 21p and 21q22. The molecular content of the ring chromosome was determined using quantitative Southern blot analyses of 5 random DNA sequences and 4 expressed genes assigned to chromosome 21 and mapping in the region of q22.3. We have shown that collagen type VI, alpha 2 (COL6A2,) S100 protein, beta polypeptide (neural), (S100B), and D21S44 are present in only one copy in both ring carriers, while CRYA1, CBS, D21S43, D21S42, D21S41, and D21S39 are present in two copies. These data and the breakpoints defining the deletion in these patients show that deletion of COL6A2 and S100B is compatible with normal function and confirm the physical map of 21q22.3 by placing COL6A2, S100B, and D21S44 in very distal 21q22.3. Patients with such small deletions provide unique models for understanding the biological and clinical significance of aneuploidy for specific expressed genes.

Recently, a gene causing familial Alzheimer disease (FAD) was linked to DNA probes on chromosome 21 by genetic analysis. To investigate the precise physical location of these DNA probes, we have constructed a physical map of this region of chromosome 21 by using quantitative Southern blot analysis of cell lines aneuploid for parts of chromosome 21. The following DNA sequences were investigated: D21S16, D21S13, FB68L (cDNA probe for the amyloid protein precursor [APP] gene), and D21S1. We find that all DNA probes are located in the same region of chromosome 21, in q11.2-q21.05. We further show that D21S16 must be centromeric to D21S13, because D21S16, but not D21S13 is present in one copy in a cell line with deletion of the region 21pter-21q 11.2. High resolution chromosome analysis is presented to define this breakpoint. This new panel of aneuploid cell lines will allow the rapid mapping of new DNA probes in the vicinity of the FAD gene.

The gene for von Recklinghausen neurofibromatosis (NF1) is on proximal 17q; the location of the gene for achondroplasia (ACH) is unknown. We have begun a molecular analysis of a patient with mental retardation, NF1 and ACH, a clinical presentation suggestive of a contiguous gene syndrome. In addition, this individual has a 47,XYY chromosome constitution. To define a possible chromosome 17 deletion, we investigated the copy number of DNA sequences linked to NF1 with conventional and pulsed-field gel electrophoresis (PFGE). We found no evidence for a deletion on chromosome 17. These results make it unlikely that this patient harbors a single deletion in the NF1 region causing both NF1 and ACH and suggest different mechanisms for the de novo occurrence of 2 autosomal dominant disorders in this individual.

Using a molecular analysis of the DNA from a patient with a deletion of chromosome 20 [46,XX,del(20)(p 11.23)], we have excluded the growth hormone-releasing hormone (GHRH) gene from the region 20p11.23----pter. The patient had minor facial anomalies. Rieger eye anomaly, a congenital heart defect, severe failure to thrive, and a neurosecretory problem in growth hormone (GH) secretion. Since the GHRH gene was previously mapped to chromosome 20, we used molecular genetic methods to determine whether the growth abnormalities were due to the deletion of this gene. DNAs of the patient and 2 normal control subjects were analyzed by quantitative Southern blotting using a DNA probe for the GHRH gene and 2 reference DNA probes mapping to chromosome 21. The GHRH gene was found to be present in 2 copies in the patient. This indicates that the gene for GHRH maps to the region outside the patient's deletion, in 20p11.23----qter. Furthermore, our results suggest that genes other than GHRH on 20p are important for developmental steps leading to normal neurosecretory function of GH and may also be involved in generating Rieger eye anomaly. Finally, GH deficiency and Rieger eye anomaly should be sought in other patients with deletions of 20p.

Down syndrome (DS) is a major cause of mental retardation and heart disease. Although it is usually caused by the presence of an extra chromosome 21, a subset of the diagnostic features may be caused by the presence of only band q22. Molecular and cytogenetic analysis of a family with 4 DS members has significantly narrowed the chromosomal region responsible for the DS phenotype: congenital heart disease, facial features, and possibly dermatoglyphics. Using high-resolution chromosome banding and in situ hybridization, we found the DS phenotype in the family is caused by a duplication of chromosome 21 material including a region of distal band q22.1 below the limit of cytogenetic resolution, in addition to bands q22.2-q22.3. By quantitative Southern blot analyses of DS members of the family, all random DNA sequences and expressed genes mapping in band q22.1 and proximal are found not to be duplicated. These include cDNA probes for the genes for superoxide dismutase (SOD1) mapping in 21q22.1 and for the amyloid precursor protein (APP) mapping in 21q21.05; D21S46 in 21q11.2-21.05; and D21S47 and SF57 in 21q22.1-q22.3. With one exception, DNA sequences mapping in band q22.3 are duplicated (D21S39, D21SD42, and D21S43). This analysis has now been extended to show that D21S17, previously mapped to band 21q22.3, is not duplicated. In conclusion, the genes SOD1 and APP have been excluded from a necessary role in generating the classical DS features, and the proximal border of the chromosomal region causing DS has been defined.

Some forms of familial Alzheimer disease (FAD) have shown linkage to DNA probes for the loci D21S1 and D21S16 on chromosome 21. To investigate the physical location of these DNA probes, we have constructed a physical map of this region of chromosome 21 by using quantitative Southern blot analysis of DNA sequences unique to chromosome 21 and a series of cell lines aneuploid for parts of chromosome 21. We now show that both D21S16 and D21S1/S11 are located in the same region of chromosome 21, in q11.2-q21.05. This new panel of aneuploid cell lines will allow the rapid mapping of new DNA probes in the vicinity of the FAD gene.

A 13-year-old boy with imipramine overdose developed seizures, respiratory arrest, and coma. Abnormalities of oculovestibular reflexes, electroencephalograms, and brainstem auditory evoked potentials were monitored in relation to measurements of drug levels. An alpha-coma electroencephalographic pattern evolved into one evidencing spindle coma and eventually into a normal pattern. Prolonged brainstem auditory evoked potentials also normalized as coma and oculocephalic reflex abnormalities resolved. In spite of the history that suggested hypoxic damage, the absence of reflex eye movements in a comatose patient and the presence of alpha- and spindle-coma electroencephalographic patterns, even with prolonged brainstem auditory evoked potentials, are not reliable prognostic indicators in tricyclic drug overdose.