John Wolff

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.

The clinical and genetic spectrum of spinocerebellar ataxia 14

Spinocerebellar ataxia 14 (SCA14) is associated with missense mutations in the protein kinase C γ 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.

CMT2C with vocal cord paresis associated with short stature and mutations in the TRPV4 gene

Background: Recently, mutations in the transient receptor potential cation channel, subfamily V, member 4 gene (TRPV4) have been reported in Charcot-Marie-Tooth Type 2C (CMT2C) with vocal cord paresis. Other mutations in this same gene have been described in separate families with various skeletal dysplasias. Further clarification is needed of the different phenotypes associated with this gene. Methods: We performed clinical evaluation, electrophysiology, and genetic analysis of the TRPV4 gene in 2 families with CMT2C. Results: Two multigenerational families had a motor greater than sensory axonal neuropathy associated with variable vocal cord paresis. The vocal cord paresis varied from absent to severe, requiring permanent tracheotomy in 2 subjects. One family with mild neuropathy also manifested pronounced short stature, more than 2 SD below the average height for white Americans. There was one instance of dolichocephaly. A novel S542Y mutation in the TRPV4 gene was identified in this family. The other family had a more severe, progressive, motor neuropathy with sensory loss, but less remarkable short stature and an R315W mutation in TRPV4. Third cranial nerve involvement and sleep apnea occurred in one subject in each family. Conclusion: CMT2C with axonal neuropathy, vocal cord paresis, and short stature is a unique syndrome associated with mutations in the TRPV4 gene. Mutations in TRPV4 can cause abnormalities in bone, peripheral nerve, or both and may result in highly variable orthopedic and neurologic phenotypes.

Further localization of a gene for paroxysmal dystonic choreoathetosis to a 5-cM region on chromosome 2q34

Abstract Paroxysmal dystonic choreoathetosis (PDC) is a rare neurological disorder characterized by episodes of involuntary movement, involving the extremities and face, which may occur spontaneously or be precipitated by caffeine, alcohol, anxiety, and fatigue. PDC is transmitted as an autosomal dominant trait with incomplete penetrance. A gene implicated in this paroxysmal disorder has been mapped to a 10–15 cM region on chromosome 2q31–36 in two families. We describe a third family with PDC. Two-point linkage analyses with markers linked to the candidate PDC locus were performed. A maximum two-point LOD score of 4.20 at a recombination fraction of zero was obtained for marker D2S120, confirming linkage to the distal portion of chromosome 2q. The anion exchanger gene, SLC2C, maps to this region, but the family was poorly informative for polymorphic markers within and flanking this candidate gene. Haplotype analysis revealed a critical recombination event that confines the PDC gene to a 5-cM region bounded by the markers D2S164 and D2S377. We compared the haplotype in our family with that in another chromosome 2-linked PDC family, but did not detect a region of shared genotypes. However, identifying a third family whose disease maps to the same region and narrowing the critical region will facilitate identification of the 2q-linked PDC gene.

A novel mutation in FHL1 in a family with X-linked scapuloperoneal myopathy: Phenotypic spectrum and structural study of FHL1 mutations

An X-linked myopathy was recently associated with mutations in the four-and-a-half-LIM domains 1 (FHL1) gene. We identified a family with late onset, slowly progressive weakness of scapuloperoneal muscles in three brothers and their mother. A novel missense mutation in the LIM2 domain of FHL1 (W122C) co-segregated with disease in the family. The phenotype was less severe than that in other reported families. Muscle biopsy revealed myopathic changes with FHL1 inclusions that were ubiquitin- and desmin-positive. This mutation provides additional evidence for X-linked myopathy caused by a narrow spectrum of mutations in FHL1, mostly in the LIM2 domain. Molecular dynamics (MD) simulations of the newly identified mutation and five previously published missense mutations in the LIM2 domain revealed no major distortions of the protein structure or disruption of zinc binding. There were, however, increases in the nonpolar, solvent-accessible surface area in one or both of two clusters of residues, suggesting that the mutant proteins have a variably increased propensity to aggregate. Review of the literature shows a wide range of phenotypes associated with mutations in FHL1. However, recognizing the typical scapuloperoneal phenotype and X-linked inheritance pattern will help clinicians arrive at the correct diagnosis.

Hereditary benign chorea: Clinical and genetic features of a distinct disease

Objective: To describe a second family with benign hereditary chorea (BCH, OMIM 118700) and suggestive linkage to chromosome 14q. BCH is an autosomal dominant disorder of early onset that differs from Huntington disease in being nondementing and nonprogressive without other neurologic signs. There has been controversy regarding the existence of BCH as a discrete disorder. Background: A single kindred was recently reported with linkage of BCH to a 20.6-KcM region on chromosome 14q. Methods: In a four-generation family with BCH, linkage was evaluated to markers in a 23-KcM region between D14S49 and D14S66 that contains the putative BCH locus. Results: A multipoint nonparametric lod score of 3.01 is consistent with linkage of disease in this family to the 14q BCH locus. A recombination event in one affected individual enabled the critical region to be narrowed to 6.93 KcM flanked by D14S1068 and D14S1064. This region contains two candidate genes: glial maturation factor beta and guanosine triphosphate cyclohydrolase 1 (GCH1). Survival motor neuron (SMN) interacting protein-1 is eliminated as a candidate gene because it lies outside the critical region. No sequence alteration was identified in the coding region of GCH1 in an affected individual. Conclusion: These data provide further evidence that BCH is a distinct entity, narrow the location of BCH to a 6.93-KcM region on chromosome 14q, and exclude SMN interacting protein-1 as a candidate gene.

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).

Two Novel Mutations in ABHD12: Expansion of the Mutation Spectrum in PHARC and Assessment of their Functional Effects

PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataracts) is a recently described autosomal‐recessive neurodegenerative disease caused by mutations in the α−β−hydrolase domain‐containing 12 gene (ABHD12). Only five homozygous ABHD12 mutations have been reported and the pathogenesis of PHARC remains unclear. We evaluated a woman who manifested short stature as well as the typical features of PHARC. Sequence analysis of ABHD12 revealed a novel heterozygous c.1129A>T (p.Lys377*) mutation. Targeted comparative genomic hybridization detected a 59‐kb deletion that encompasses exon 1 of ABHD12 and exons 1–4 of an adjacent gene, GINS1, and includes the promoters of both genes. The heterozygous deletion was also carried by the patients asymptomatic mother. Quantitative reverse transcription‐PCR demonstrated ∼50% decreased expression of ABHD12 RNA in lymphoblastoid cell lines from both individuals. Activity‐based protein profiling of serine hydrolases revealed absence of ABHD12 hydrolase activity in the patient and 50% reduction in her mother. This is the first report of compound heterozygosity in PHARC and the first study to describe how a mutation might affect ABHD12 expression and function. The possible involvement of haploinsufficiency for GINS1, a DNA replication complex protein, in the short stature of the patient and her mother requires further studies.

A novel X-linked four-repeat tauopathy with Parkinsonism and spasticity.

The parkinsonian syndromes comprise a highly heterogeneous group of disorders. Although 15 loci are linked to predominantly familial Parkinsons disease (PD), additional PD loci are likely to exist. We recently identified a multigenerational family of Danish and German descent in which five males in three generations presented with a unique syndrome characterized by parkinsonian features and variably penetrant spasticity for which X‐linked disease transmission was strongly suggested (XPDS). Autopsy in one individual failed to reveal synucleinopathy; however, there was a significant four‐repeat tauopathy in the striatum. Our objective was to identify the locus responsible for this unique parkinsonian disorder. Members of the XPDS family were genotyped for markers spanning the X chromosome. Two‐point and multipoint linkage analyses were performed and the candidate region refined by analyzing additional markers. A multipoint LODmax score of 2.068 was obtained between markers DXS991 and DXS993. Haplotype examination revealed an ∼20 cM region bounded by markers DXS8042 and DXS1216 that segregated with disease in all affected males and obligate carrier females and was not carried by unaffected at‐risk males. To reduce the possibility of a false‐positive linkage result, multiple loci and genes associated with other parkinsonian or spasticity syndromes were excluded. In conclusion, we have identified a unique X‐linked parkinsonian syndrome with variable spasticity and four‐repeat tau pathology, and defined a novel candidate gene locus spanning ∼28 Mb from Xp11.2–Xq13.3.