Calpainopathy presenting as foot drop in a 41 year old.

Mutations in the gene encoding muscle-specific calpain 3 protease cause limb girdle muscular dystrophy type 2A. Calpainopathy is characterised by progressive symmetrical atrophy of pelvic, scapular and trunk muscles with an elevated creatine kinase. Most patients develop symptoms in childhood and lose the ability to walk by the age of 40 years. We describe a man who presented with foot drop at the age of 41 years, together with neurophysiological, histopathological and genetic data. This is the first report of calpainopathy presenting as foot drop, and widens the phenotype associated with this disease.

Large scale calcium channel gene rearrangements in episodic ataxia and hemiplegic migraine: implications for diagnostic testing.

BACKGROUND: Episodic ataxia type 2 (EA2) and familial hemiplegic migraine type 1 (FHM1) are autosomal dominant disorders characterised by paroxysmal ataxia and migraine, respectively. Point mutations in CACNA1A, which encodes the neuronal P/Q-type calcium channel, have been detected in many cases of EA2 and FHM1. The genetic basis of typical cases without CACNA1A point mutations is not fully known. Standard DNA sequencing methods may miss large scale genetic rearrangements such as deletions and duplications. The authors investigated whether large scale genetic rearrangements in CACNA1A can cause EA2 and FHM1. METHODS: The authors used multiplex ligation dependent probe amplification (MLPA) to screen for intragenic CACNA1A rearrangements. RESULTS: The authors identified five previously unreported large scale deletions in CACNA1A in seven families with episodic ataxia and in one case with hemiplegic migraine. One of the deletions (exon 6 of CACNA1A) segregated with episodic ataxia in a four generation family with eight affected individuals previously mapped to 19p13. In addition, the authors identified the first pathogenic duplication in CACNA1A in an index case with isolated episodic diplopia without ataxia and in a first degree relative with episodic ataxia. CONCLUSIONS: Large scale deletions and duplications can cause CACNA1A associated channelopathies. Direct DNA sequencing alone is not sufficient as a diagnostic screening test.

Oculopharyngeal muscular dystrophy: a point mutation which mimics the effect of the PABPN1 gene triplet repeat expansion mutation.

BACKGROUND: Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant late onset neuromuscular disease characterised by proximal muscle weakness, ptosis, and swallowing difficulty. The only causative mutation described to date is a triplet repeat expansion consisting of two to seven additional base triplets in a repeat sequence in exon 1 of the polyadenine binding protein nuclear 1 (PABPN1) gene. This results in an increase in length of a polyalanine tract in the PABPN1 protein from 10 to 12-17 residues. OBJECTIVE: Description of another mutation in a case of OPMD. METHODS: Sequence analysis of exon 1 of the PABPN1 gene was undertaken on 202 patients referred for a possible diagnosis of OPMD but negative for the triplet repeat expansion mutation. RESULTS: A case was identified with typical symptoms of OPMD, negative for the repeat expansion mutation but with a missense mutation in PABPN1 close to the 3' end of the normal polyalanine codon repeat sequence. CONCLUSIONS: The single base mutation changes a glycine codon to an alanine codon and results in an increase in the number of contiguous polyalanine codons. This mimics the effect of the common triplet repeat expansion mutation and represents a previously undescribed mechanism of mutation.

Allgrove or 4 "A" syndrome: an autosomal recessive syndrome causing multisystem neurological disease.

Allgrove's or "4 A" syndrome is a rare autosomal recessive condition with alacrima, achalasia, autonomic disturbance, and ACTH insensitivity among other features. Recent studies have identified mutations in the AAAS, a candidate gene on chromosome 12q13 in such patients. Manifestations in adult patients are rarely reported. The syndrome usually presents during the first decade of life with dysphagia or severe (occasionally fatal) hypoglycaemic or hypotensive attacks, related to adrenocortical insufficiency. Onset of adrenal insufficiency or other features may be delayed to adulthood. In contrast with paediatric patients, adult patients with Allgrove's syndrome may present with multisystem neurological disease; the childhood history of achalasia or alacrima may be overlooked. The authors describe two families with two affected siblings and a further unrelated patient with typical clinical features of Allgrove's syndrome, who exhibit signs of multisystem neurological disease including hyperreflexia, muscle wasting, dysarthria, ataxia, optic atrophy, and intellectual impairment. None of the cases have developed adrenal insufficiency but all have progressive neurological disability. Autonomic dysfunction was a significant cause of morbidity in two cases. The three index cases represent the longest described follow up of Allgrove's syndrome into adulthood. It is speculated that they represent a subgroup of patients who follow an often undiagnosed chronic neurological course. Recognition of the syndrome presenting in adult life permits treatment of unrecognised autonomic dysfunction, adrenal insufficiency and dysphagia, and appropriate genetic advice.

A study of mitochondrial DNA mutations in peripheral lymphocytes in an aging cohort.

Somatic mutation in the mitochondrial genome occurs much more rapidly than in the nuclear genome and is a feature, possibly contributory, of the aging of cells and tissues. Identifying mitochondrial sequence changes in blood DNA of elderly subjects may provide a maker for the epigenetic changes of mitochondrial DNA known to occur in tissues with lower cellular turnover, and would also have implications for immunosenescence. No large-scale epidemiological studies have been reported previously. In this study we have established long-PCR banks of the mitochondrial genome from peripheral lymphocytes for an elderly cohort of 716 individuals with a range of measured aging phenotypes, and we have established assays for three widely reported mutations: the 4977 bp and 8048 bp deletions and point mutation A3243G. No individuals were identified with detectable heteroplasmy for these changes. Implications for tissue and population prevalence are discussed. The mitochondrial long-PCR DNA banks established will be useful for a wide range of studies of somatic mutation and of germline haplotypes in relation to aging.

Oculopharyngeal muscular dystrophy: phenotypic and genotypic studies in a UK population.

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant disorder of late onset that commonly presents with ptosis and dysphagia. The genetic basis of the condition has been identified recently as a stable trinucleotide repeat expansion in exon 1 of the poly(A) binding protein 2 gene (PABP2), in which (GCG)(6) is the normal repeat length. The prevalence of OPMD is greatest in patients of French-Canadian origin. It is not clear if expansion repeat length is a reliable test in other populations. In this study, we analysed the phenotypic and genotypic characteristics of 31 patients with OPMD in the UK. Ptosis was the first reported symptom in two-thirds of the patients, and half of the subjects studied had evidence of ophthalmoplegia. All but one family had a pathological expansion in the PABP2 gene, ranging from (GCG)(8) to (GCG)(13). In contrast to the French-Canadian population, (GCG)(10) was almost as common as (GCG)(9), evidence against a strong founder effect in the UK population. There was a weak association between repeat length and age of disease onset. Patients with longer repeat lengths, such as (GCG)(13), developed severe limb weakness early in the disease. We were unable to detect the (GCG)(7) polymorphism in over 200 normal controls, suggesting that the frequency of this expansion is lower than that found in the French-Canadian population. One family was negative for the expansion. Affected members presented with the classical features of OPMD, namely ptosis, dysphagia and cytoplasmic inclusions on muscle biopsy, although with some atypical features, such as early age of onset, high serum levels of creatine kinase and a profound ophthalmoplegia. This family is an example of a GCG expansion-negative oculopharyngeal syndrome requiring further genetic investigation. We conclude that PABP2 analysis is a reliable non-invasive diagnostic test for OPMD in the UK population.

X-linked sideroblastic anaemia with ataxia: another mitochondrial disease?

OBJECTIVES: The syndrome of X-linked sideroblastic anaemia with ataxia is rare, described only twice in the literature. The aim was to obtain clinical neurological and haematological data about this rare syndrome throughout adult life. METHODS: A family is described with two affected brothers and two affected maternal uncles. The family was evaluated clinically. Haematological investigations included full blood count, blood film, iron studies, free erythrocyte protoporphyrin (FEP) concentrations and a bone marrow examination where possible. RESULTS: Core neurological features included motor delay, ataxia evident from early childhood, and dysarthria. Neurological features were non-progressive until the fifth decade when slow progression became evident. Some family members showed mild spasticity. Patients usually have a mild asymptomatic anaemia or a borderline decreased mean corpuscular volume. Blood film examination showed Pappenheimer bodies. Bone marrow examination showed ring sideroblasts, indicating raised erythrocyte iron. Free erythrocyte protoporphyrin (FEP) concentrations were raised. CONCLUSIONS: Haematological features are subtle and can be easily overlooked, and individual patients may not display all the abnormal features. X-linked ataxias are rare and incorrect genetic advice may be given if the diagnostic haematological features of X-linked sideroblastic anaemia are overlooked. Males with early onset ataxia should have a haematological evaluation including a blood film, with a bone marrow examination if abnormal blood count indices and measurement of FEP concentrations raise suspicion. The condition has parallels with Pearson's syndrome and Friedreich's ataxia. All three conditions are associated with mitochondrial iron handling defects and ataxia. The human ATP binding cassette gene (hABC7) is a candidate gene and requires further investigation.

A clinical and genetic study of a manifesting heterozygote with X-linked myotubular myopathy.

X-linked myotubular myopathy (XLMTM) characteristically causes severe or fatal muscle weakness in male infants. Mutations in the gene MTM1, encoding the protein myotubularin, can be identified in most families. Prior to this report, XLMTM was thought not to cause symptomatic manifestations in female carriers. We describe an adult female from a large family with typical XLMTM. The patient had progressive disabling muscle weakness of later onset and lesser severity than that observed in affected males. The distribution of weakness resembled typical XLMTM with facial weakness, marked limb-girdle weakness, respiratory muscle involvement and dysphagia. Analysis of the MTM1 gene identified a heterozygous missense mutation (G378R) within the highly conserved tyrosine phosphatase site of myotubularin. We did not identify significantly skewed X-inactivation. We conclude that XLMTM is capable of causing significant disability in heterozygotes.

Ataxia with isolated vitamin E deficiency presenting as mutation negative Friedreich's ataxia.

Ataxia with vitamin E deficiency is an autosomal recessive condition associated with a defect in the a-tocopherol transfer protein. Clinically it manifests as a progressive ataxia with a phenotype resembling that of Friedreich's ataxia. There is some evidence that progression of neurological symptoms is prevented by vitamin E therapy. A patient is described who was given a clinical diagnosis of Friedreich's ataxia. Molecular genetic analysis showed the absence of the frataxin gene expansion. Subsequent vitamin E assay showed deficiency and a diagnosis of ataxia with vitamin E deficiency was made. It is recommended that all patients with ataxia of unknown cause should have vitamin E deficiency excluded. When a diagnosis of Friedreich's ataxia is considered patients should have frataxin analysis in addition. Further, neurologists should be aware that ataxia with vitamin E deficiency may present as "mutation negative" Friedreich's ataxia.

A mitochondrial DNA tRNA(Val) point mutation associated with adult-onset Leigh syndrome.

Subacute necrotizing encephalomyelopathy (Leigh syndrome) is associated with a number of mitochondrial DNA (mtDNA) abnormalities. We studied a family with maternally inherited encephalomyelopathy. Two siblings developed adult-onset Leigh syndrome. Muscle biopsy specimens showed enhanced succinic dehydrogenase activity and cytochrome oxidase-negative fibers. We sequenced the ATPase- and transfer RNA (tRNA)-encoding genes of mtDNA and identified a novel mtDNA valine tRNA mutation at base pair 1644. This transversion was heteroplasmic in blood and muscle in all individuals studied, and the proportion of mutant mtDNA correlated with disease severity. This is the first heteroplasmic transversion within a mtDNA tRNA gene and the second pathogenic mtDNA tRNA(Val) mutation to be associated with human disease.

The mitochondrial DNA transfer RNALeu(UUR) A-->G(3243) mutation. A clinical and genetic study.

The mitochondrial tRNALeu(UUR) A-->G(3243) mutation was identified in 22 unrelated patients. The probands and their relatives were assessed clinically and by quantitative mitochondrial DNA (mtDNA) analysis. While 10 probands had clinical features consistent with the syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), usually associated with this mutation, 12 probands had other phenotypes including other encephalopathies, chronic progressive external ophthalmoplegia (CPEO), myoclonic epilepsy and ragged red fibres (MERRF), myopathy alone and diabetes and deafness. Histochemical analyses of muscle biopsies showed a higher proportion of cytochrome oxidase (COX) negative fibres, but fewer strongly COX reactive fibres, in patients with CPEO compared with those with MELAS. The proportion of mutant mtDNA present in blood was significantly greater in symptomatic than asymptomatic subjects, and was correlated with age in both. This correlation was not observed in patients with the tRNALys A-->G(8344) mutation. The proportion of mutant mtDNA A-->G(3243) in muscle was always greater than that in blood. Significant correlations between proportion of mutant mtDNA in blood and both age of onset of disease and a clinical severity score were observed. However, the proportion of mutant mtDNA in blood in affected and unaffected cases overlapped, preventing use of the genetic-clinical correlation for prognostic or predictive purposes. The presence of intrafamilial clustering of phenotypes and the imperfect relationship between proportion of mutant mtDNA and the presence or absence of disease suggests that other factors may determine the phenotype. To investigate this possibility further, the tRNALeu(UUR) gene was sequenced in 23 probands and six relatives. In 28 patients the sequence was normal apart from the 3243 mutation, but in members of one family there was a homoplasmic T-->C transition at position 3290 which was not found in 140 controls or 50 other patients with mitochondrial myopathy. The family with this transition had high levels of mutant mtDNA A-->G(3243), with a unique phenotype of predominant skeletal myopathy, suggesting that this second base change in tRNALeu(UUR) may influence the clinical phenotype.

Mitochondrial DNA (mtDNA) diseases: correlation of genotype to phenotype.

This study examines the relationship of genotype to phenotype in 14 unselected patients who were found to harbour the A3243G transition in the mitochondrial transfer RNALeu(UUR) gene commonly associated with the syndrome of mitochondrial encephalopathy, lactic acidosis and strokes (MELAS). Only 6 of the 14 cases (43%) had seizures and recurrent strokes, the core clinical features of the MELAS phenotype. Of the remaining cases, four had an encephalomyopathy with deafness, ataxia and dementia, two had syndromes with progressive external ophthalmoplegia and two had limb weakness alone. Even within the MELAS subgroup, the majority of patients had one or more clinical manifestations considered to be atypical of the MELAS syndrome. They included developmental delay, ophthalmoparesis, pigmentary retinopathy and intestinal pseudo-obstruction. The proportion of mutant mitochondrial DNA (mtDNA) in muscle was generally higher in patients with recurrent strokes than in those without strokes, the highest levels being observed in MELAS cases with early onset disease. Studies of isolated muscle mitochondria identified a range of respiratory chain abnormalities mostly involving Complex I; immunoblots of Complex I in 3 of 10 cases showed selective loss of specific subunits encoded by nuclear genes. In the group as a whole, however, no clear correlations were observed between the severity or extent of the respiratory chain abnormality and clinical phenotype or the proportion of mutant mtDNA in biopsied skeletal muscle. These discrepancies suggest that, in patients harbouring the common MELAS3243 mutation, differences in heteroplasmy and the proportions of mutant mtDNA may not be the sole determinants of disease expression and that additional genetic mechanisms are involved in defining the range of clinical and biochemical phenotypes associated with this aberrant mitochondrial genome.

Cortical reflex myoclonus in patients with the mitochondrial DNA transfer RNA(Lys)(8344) (MERRF) mutation.

Five patients from three families with the syndrome of myoclonic epilepsy and ragged red fibres (MERRF), associated with the mitochondrial DNA point mutation at position 8344, were studied neurophysiologically to determine the characteristics of their myoclonus. The findings were those of cortical reflex myoclonus, with enlarged cortical somatosensory evoked potentials and late reflex responses to peripheral nerve stimulation. Electroencephalography showed paroxysmal spike and polyspike and wave discharges, with photic sensitivity. This pattern of electrophysiological abnormalities was uniform, despite considerable variation in severity of myoclonus. Although a consistent finding, cortical reflex myoclonus is not specific to MERRF amongst myoclonic syndromes.