Hillary P. Lipe

Missense Mutations in the Regulatory Domain of PKCγ: A New Mechanism for Dominant Nonepisodic Cerebellar Ataxia

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.

Cerebral cavernous malformation: novel mutation in a Chinese family and evidence for heterogeneity.

Familial cerebral cavernous malformation (CCM) is an autosomal dominant disorder producing vascular anomalies throughout the central nervous system associated with seizures and hemorrhagic stroke. Linkage analysis has shown evidence for at least three genetic loci underlying this disorder with a founder mutation in the Mexican/Hispanic community. We report the first family of Chinese ethnic origin with CCM having a novel mutation in the CCM1 gene. The mutation in exon 19 causes a premature stop codon (Q698X) predicted to produce a truncated Krev1 interaction-trapped 1 (KRIT1) protein. Members of the family with this mutation have a wide range in age of onset with seizures, ataxia, spinal cord vascular malformation, headaches and skin lesions. An additional unrelated sporadic subject with brain lesions compatible with CCM as well as vascular skin findings suggesting the blue rubber bleb nevus (BRBN) syndrome has no mutation detected in the CCM1 gene. These findings expand the phenotype of and demonstrate further evidence for the heterogeneity in the CCM syndrome.

Late onset Huntington Disease: clinical and genetic characteristics of 34 cases.

We performed a retrospective observational study of thirty-four persons with late onset of Huntington Disease (HD) (onset range 60-79 years). CAG trinucleotide expansion size ranged from 38-44 repeats. Even at this late age a significant negative correlation (r=-0.421, p<0.05) was found between the length of repeat and age of onset. Important characteristics of these older subjects were: (1)Most (68%) were the first in the family to have a diagnosis of HD, (2) Motor problems were the initial symptoms at onset, (3) Disability increased and varied from mild to severe (4) Disease duration was somewhat shorter (12 years) than that reported for mid-life onset, (5) Death was often related to diseases of old age, such as cancer and cerebrovascular disease, (6) Serious falls were a major risk and (7) Global dementia may be associated with coincident Alzheimer disease. Recognizing these characteristics will help physicians and other health care providers better identify and follow the late onset presentation of this disease.

Familial dyskinesia and facial myokymia (FDFM): A novel movement disorder

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. Ann Neurol 2001;49:486–492

Familial spastic paraparesis: Evaluation of locus heterogeneity, anticipation, and haplotype mapping of the SPG4 locus on the short arm of chromosome 2

Familial spastic paraparesis (SPG) is a clinically and genetically heterogeneous group of disorders. At least three loci have been implicated in autosomal dominant pure SPG and mutations in either of two loci may cause the X-linked form. Although the penetrance is high for all forms by age 60, there is wide variation in clinical characteristics, including age of onset. Two-point and multi-point linkage analyses in nine families provided supportive evidence that the most common form of SPG is linked to chromosome 2 (SPG4). Haplotype analysis localized the critical region to a 6 cM interval between D2S392 and D2S367. By haplotype analysis, the disease in at least one family does not appear to be linked to any of the presently known SPG loci, suggesting that there is at least one additional SPG gene. Evaluation at ages of onset in 11 families gave suggestive evidence for anticipation with mean age of onset in parents (41.3 years) being older than mean age of onset in children (26.9 years; P < 0.005).

Familial aggregation of schizophrenia-like symptoms in huntington's disease

An increased incidence of schizophrenia-like symptoms in Huntingtons disease (HD) has been well-documented in the past. The reasons for this association, however, have never been explained. At the University of Washington Medical Genetics Clinic, we had the opportunity to evaluate a unique juvenile-onset HD proband who had schizophrenia-like symptoms. This patient was referred to our clinic because of new onset of somatic delusions and command auditory hallucinations early in the course of her illness. Since we had already evaluated other affected individuals in her family, we selected another family with a nonpsychotic juvenile-onset proband for comparison. Using these two families in a small case-control study, we investigated the following hypotheses which could explain the association between schizophrenia-like symptoms and HD: first, schizophrenia-like symptoms may be related to the number of CAG repeats in the HD gene; second, schizophrenia-like symptoms may segregate in certain HD families, for unknown reasons; and third, there may coincidentally be an unrelated gene for schizophrenia in certain HD families. Comparisons of clinical characteristics and the HD genotype showed that family history of schizophrenia-like symptoms segregated with the HD gene; however, age of onset of HD, size of CAG repeat, and sex of the transmitting parent were not associated with psychotic symptoms. Further genetic and neurobiological studies are necessary to investigate the potential mechanism underlying this association.

Familial dyskinesia and facial myokymia (FDFM): Follow-up of a large family and linkage to chromosome 3p21-3q21.

We previously reported a five‐generation family manifesting an autosomal dominant disorder of facial myokymia and dystonic/choreic movements (FDFM). The dyskinetic episodes are initially paroxysmal but may become constant. With increasing age they may lessen or even disappear. The previous study excluded nine candidate genes chosen for their association with myokymia or chorea and two regions containing single or clustered ion channel genes. We now report identification by whole genome linkage analysis of a broad region on chromosome 3p21‐3q21 that segregates with the disease in all 10 affected members in three generations who participated in the study. GENEHUNTER‐MODSCORE Version 2.0.1 provided a maximum multipoint LOD score of 3.099. No other disorders primarily characterized by myokymia, dystonia, or chorea are known to map to this region. Identification of additional families with FDFM may narrow the critical region and facilitate the choice of candidate genes for further analysis.

Geriatric Neurogenetics: Oxymoron or Reality?

BACKGROUND Primary genetic diseases are generally associated with pediatric and young adult populations. Little information is available about the occurrence of single-gene mendelian diseases in elderly populations. OBJECTIVE To describe the occurrence of single-gene neurogenetic disorders in a group of elderly patients. DESIGN Retrospective review of neurogenetic cases in an academic medical center. SETTING Academic university and Veterans Affairs medical centers. PATIENTS Eight elderly patients with single-gene neurogenetic diseases were studied. These patients included an 87-year-old man and an 85-year-old man with Huntington disease, an 84-year-old woman with limb-girdle muscular dystrophy type 2A, a 78-year-old man with spinocerebellar ataxia type 14, an 86-year-old man with spinocerebellar ataxia type 5, an 85-year-old man with a presenilin 1 familial Alzheimer disease mutation, an 87-year-old man with autosomal dominant hereditary neuropathy, and a 78-year-old man with spinocerebellar ataxia type 6. Three patients had no family history of neurologic disease. MAIN OUTCOME MEASURES Medical histories, physical examination results, and genetic testing results. CONCLUSIONS Single-gene mendelian neurogenetic diseases can be found in the oldest old population (> 85 years). Such cases are currently underrecognized and will become more commonly observed in the future. This phenomenon is a result of (1) the aging of the general population, (2) better recognition of the highly variable ages at onset of genetic diseases, and (3) the availability of specific DNA-based genetic testing.