Mitochondrial defects have been associated with neurological disorders, as well as cancers. Two ubiquitously expressed mitochondrial enzymes--succinate dehydrogenase (SDH) and fumarate hydratase (FH, fumarase)--catalyse sequential steps in the Krebs tricarboxylic-acid cycle. Inherited heterozygous mutations in the genes encoding these enzymes cause predispositions to two types of inherited neoplasia syndromes that do not share any component tumours. Homozygous mutations in the same genes result in severe neurological impairment. Understanding this link between inherited cancer syndromes and neurological disease could provide further insights into the mechanisms by which mitochondrial deficiencies lead to tumour development.

Germline intragenic mutations in PTEN are associated with 80% of patients with Cowden syndrome (CS) and 60% of patients with Bannayan-Riley-Ruvalcaba syndrome (BRRS). The underlying genetic causes remain to be determined in a considerable proportion of classic CS and BRRS without a polymerase chain reaction (PCR)-detectable PTEN mutation. We hypothesized that gross gene deletions and mutations in the PTEN promoter might alternatively account for a subset of apparently mutation-negative patients with CS and BRRS. Using real time and multiplex PCR techniques, we identified three germline hemizygous PTEN deletions in 122 apparently mutation-negative patients with classic CS (N=95) or BRRS (N=27). Fine mapping suggested that one deletion encompassed the whole gene and the other two included exon 1 and encompassed exons 1-5 of PTEN, respectively. Two patients with the deletion were diagnosed with BRRS, and one patient with the deletion was diagnosed with BRRS/CS overlap (features of both). Thus 3 (11%) of 27 patients with BRRS or BRRS/CS-overlap had PTEN deletions. Analysis of the PTEN promoter revealed nine cases (7.4%) harboring heterozygous germline mutations. All nine had classic CS, representing almost 10% of all subjects with CS. Eight had breast cancers and/or benign breast tumors but, otherwise, oligo-organ involvement. PTEN protein analysis, from one deletion-positive and five PTEN-promoter-mutation-positive samples, revealed a 50% reduction in protein and multiple bands of immunoreactive protein, respectively. In contrast, control samples showed only the expected band. Further, an elevated level of phosphorylated Akt was detected in the five promoter-mutation-positive samples, compared with controls, indicating an absence of or marked reduction in functional PTEN. These data suggest that patients with BRRS and CS without PCR-detected intragenic PTEN mutations be offered clinical deletion analysis and promoter-mutation analysis, respectively.

We report a nonepisodic autosomal dominant (AD) spinocerebellar ataxia (SCA) not caused by a nucleotide repeat expansion that is, to our knowledge, the first such SCA. The AD SCAs currently comprise a group of > or =16 genetically distinct neurodegenerative conditions, all characterized by progressive incoordination of gait and limbs and by speech and eye-movement disturbances. Six of the nine SCAs for which the genes are known result from CAG expansions that encode polyglutamine tracts. Noncoding CAG, CTG, and ATTCT expansions are responsible for three other SCAs. Approximately 30% of families with SCA do not have linkage to the known loci. We recently mapped the locus for an AD SCA in a family (AT08) to chromosome 19q13.4-qter. A particularly compelling candidate gene, PRKCG, encodes protein kinase C gamma (PKC gamma), a member of a family of serine/threonine kinases. The entire coding region of PRKCG was sequenced in an affected member of family AT08 and in a group of 39 unrelated patients with ataxia not attributable to trinucleotide expansions. Three different nonconservative missense mutations in highly conserved residues in C1, the cysteine-rich region of the protein, were found in family AT08, another familial case, and a sporadic case. The mutations cosegregated with disease in both families. Structural modeling predicts that two of these amino acid substitutions would severely abrogate the zinc-binding or phorbol ester-binding capabilities of the protein. Immunohistochemical studies on cerebellar tissue from an affected member of family AT08 demonstrated reduced staining for both PKC gamma and ataxin 1 in Purkinje cells, whereas staining for calbindin was preserved. These results strongly support a new mechanism for neuronal cell dysfunction and death in hereditary ataxias and suggest that there may be a common pathway for PKC gamma-related and polyglutamine-related neurodegeneration.

Mutations in the parkin gene occur among individuals with PD with an older age at onset (> or =60 years) who have a positive family history of the disease. In addition, the clinical findings of parkin-positive individuals are remarkably similar to those without mutations.

We describe here familial dyskinesia and facial myokymia (FDFM), a novel autosomal dominant disorder characterized by adventitious movements that sometimes appear choreiform and that are associated with perioral and periorbital myokymia. We report a 5-generation family with 18 affected members (10 males and 8 females) with FDFM. The disorder has an early childhood or adolescent onset. The involuntary movements are paroxysmal at early ages, increase in frequency and severity, and may become constant in the third decade. Thereafter, there is no further deterioration, and there may even be improvement in old age. The adventitious movements are worsened by anxiety but not by voluntary movement, startle, caffeine, or alcohol. The disease is socially disabling, but there is no intellectual impairment or decrease in lifespan. A candidate gene and haplotype analysis was performed in 9 affected and 3 unaffected members from 3 generations of this family using primers for polymorphic loci closely flanking or within genes of interest. We excluded linkage to 11 regions containing genes associated with chorea and myokymia: 1) the Huntington disease gene on chromosome 4p; 2) the paroxysmal dystonic choreoathetosis gene at 2q34; 3) the dentatorubral-pallidoluysian atrophy gene at 12p13; 4) the choreoathetosis/spasticity disease locus on 1p that lies in a region containing a cluster of potassium (K+) channel genes; 5) the episodic ataxia type 1 (EA1) locus on 12p that contains the KCNA1 gene and two other voltage-gated K+ channel genes, KCNA5 and KCNA6; 6) the chorea-acanthocytosis locus on 9q21; 7) the Huntington-like syndrome on 20p; 8) the paroxysmal kinesigenic dyskinesia locus on 16p11.2-q11.2; 9) the benign hereditary chorea locus on 14q; 10) the SCA type 5 locus on chromosome 11; and 11) the chromosome 19 region that contains several ion channels and the CACNA1A gene, a brain-specific P/Q-type calcium channel gene associated with ataxia and hemiplegic migraine. Our results provide further evidence of genetic heterogeneity in autosomal dominant movement disorders and suggest that a novel gene underlies this new condition.

Spinocerebellar ataxia 14 (SCA14) is associated with missense mutations in the protein kinase C gamma gene (PRKCG), rather than a nucleotide repeat expansion. In this large-scale study of PRKCG in patients with ataxia, two new missense mutations, an in-frame deletion, and a possible splice site mutation were found and can now be added to the four previously described missense mutations. The genotype/phenotype correlations in these families are described.

Parkinson disease (PD) is the second most common neurodegenerative disorder, surpassed in frequency only by Alzheimer disease. Elsewhere we have reported linkage to chromosome 2q in a sample of sibling pairs with PD. We have now expanded our sample to include 150 families meeting our strictest diagnostic definition of verified PD. To further delineate the chromosome 2q linkage, we have performed analyses using only those pedigrees with the strongest family history of PD. Linkage analyses in this subset of 65 pedigrees generated a LOD score of 5.1, which was obtained using an autosomal dominant model of disease transmission. This result strongly suggests that variation in a gene on chromosome 2q36-37 contributes to PD susceptibility.

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