| #607459 | |||||||||||||||||||||||||||
| SENSORY ATAXIC NEUROPATHY, DYSARTHRIA, AND OPHTHALMOPARESIS; SANDO | |||||||||||||||||||||||||||
| Alternative titles; symbols | |||||||||||||||||||||||||||
| SENSORY ATAXIC NEUROPATHY WITH MITOCHONDRIAL DNA DELETIONS, AUTOSOMAL RECESSIVE | |||||||||||||||||||||||||||
| Other entities represented in this entry: | |||||||||||||||||||||||||||
| SPINOCEREBELLAR ATAXIA WITH EPILEPSY, INCLUDED; SCAE, INCLUDED | |||||||||||||||||||||||||||
| Phenotype Gene Relationships | |||||||||||||||||||||||||||
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| Clinical Synopsis | |||||||||||||||||||||||||||
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| A number sign (#) is used with this entry because sensory ataxic neuropathy, dysarthria, and ophthalmoparesis (SANDO) is caused by homozygous or compound heterozygous mutation in the nuclear-encoded DNA polymerase-gamma gene (POLG; 174763). Recessive mutations in the POLG gene can also cause autosomal recessive progressive external ophthalmoplegia (PEOB; 258450), which shows overlapping features. | |||||||||||||||||||||||||||
| Description | |||||||||||||||||||||||||||
| SANDO is an autosomal recessive systemic disorder characterized mainly by adult onset of sensory ataxic neuropathy, dysarthria, and ophthalmoparesis (SANDO) resulting from mitochondrial dysfunction and associated with mtDNA depletion in skeletal muscle and peripheral nerve tissue (Fadic et al., 1997). The phenotype varies widely, even within the same family, and can include myopathy, seizures, and hearing loss, but the common clinical feature appears to be sensory ataxia (review by Milone and Massie, 2010). Spinocerebellar ataxia with epilepsy (SCAE) is a similar disorder with a higher frequency of migraine headaches and seizures (Winterthun et al., 2005). | |||||||||||||||||||||||||||
| Clinical Features | |||||||||||||||||||||||||||
| Fadic et al. (1997) reported 4 unrelated patients with adult onset of severe sensory ataxic neuropathy in association with dysarthria and chronic progressive external ophthalmoplegia. Patients had ataxic gait, loss of distal proprioception and vibration, areflexia in the lower limbs, positive Romberg sign, and electrophysiologic and pathologic evidence of a peripheral axonal neuropathy. Other variable features included migraine and depression. Skeletal muscle biopsy showed myopathic changes with centralized nuclei and ragged-red fibers. Molecular analysis detected multiple mitochondrial DNA (mtDNA) deletions, ranging in size from 4.5 to 10 kb, in muscle and peripheral nerve. Fadic et al. (1997) proposed the term 'SANDO.' Rantamaki et al. (2001) reported a family in which 3 of 5 sibs were affected by progressive ataxia starting at age 30 years. Each patient showed gait and limb ataxia, dysarthria, dysphagia, nystagmus, hyporeflexia, decreased vibration and position sense, and mild cognitive impairment. One patient had epilepsy. MRI showed bilateral thalamic lesions and high-intensity signals in the cerebellar white matter. Measurements of sensory action potentials were consistent with a sensory axonal neuropathy and suggested a disorder of the central somatosensory pathways. Postmortem examination of 1 case revealed degenerative pathology and atrophic changes in the thalamus, brainstem, cerebellum, and spinal cord. The authors concluded that the disorder was most consistent with an autosomal recessive pattern of inheritance. Genetic analyses for mutations in the FXN gene (606829), several spinocerebellar ataxias, and mitochondrial diseases were negative, suggesting that this family exhibited a distinct hereditary spinocerebellar ataxia. Van Goethem et al. (2003) reported a man with SANDO who had been rejected from compulsory military service at the age of 19 years because of a disturbance of balance, which progressed slowly during the third decade and became disabling with frequent falls. He presented at age 39 with moderately severe external ophthalmoparesis, mild dysarthria, and ataxic gait without other muscle weakness. The patient showed thalamic lesions on neuroimaging. The patient's parents, both 70 years of age, were clinically normal, as was his only brother. Van Goethem et al. (2004) reported 8 patients from 5 European families who presented with sensory ataxia without apparent muscle involvement; 1 of the families had been reported by Rantamaki et al. (2001). In a previously unreported family, a man had an 8-day episode of status epilepticus at age 18 years and an acute psychiatric illness with hyperventilation, gastrointestinal symptoms, and ataxia at age 23. At age 38, he demonstrated gait and limb ataxia, dysarthria, areflexia, distal loss of vibration and proprioception in the lower limbs, a sensory axonal peripheral neuropathy, and increased CSF protein. Other features included severe gastroparesis with progressive weight loss and dilated cardiomyopathy on echocardiogram. At age 38 years, he had an acute episode of stupor, hyperventilation, myoclonus, seizures, and lactic acidosis, and died at age 39 after numerous complications. Blepharoptosis and ophthalmoparesis were never noted. A muscle biopsy at age 34 years showed abnormal mitochondrial inclusions and some evidence of mtDNA deletions. The patient's sister had acute encephalopathy, myoclonus, partial seizures, cortical blindness, stupor, and sudden death at age 17 years. In a consanguineous Belgian family, a brother and sister reported progressive gait unsteadiness beginning in adolescence. By the fifth decade, both patients had ataxic gait, areflexia, distal sensory loss in the lower limbs, axonal neuropathy, and pes cavus. In addition, the sister had gaze-evoked nystagmus, dysarthria, was wheelchair-dependent, and had symmetric cerebellar white matter lesions on MRI. The brother had mild asymptomatic upward gaze paresis, cognitive decline, and cataracts. Two additional unrelated patients had an apparently sporadic disorder with ataxia, axonal neuropathy, dysarthria, and variable eye movement abnormalities. One patient had bilateral cerebellar white matter lesions on MRI. Muscle biopsies of the patients reported by Van Goethem et al. (2004) showed no signs of mitochondrial muscle disease, consistent with the lack of clinical abnormalities. However, some muscle biopsies showed low levels of mtDNA deletions. Extraocular ophthalmoparesis was not a main feature in these patients, only developing later in the disease and often in mild forms. The findings indicated significant phenotypic heterogeneity in patients with recessive mutations in the POLG gene. Mancuso et al. (2004) reported 2 Italian sibs, a male and a female, with an autosomal recessive neurologic disorder characterized by sensorimotor polyneuropathy, ataxia, and ophthalmoparesis. Onset was in the early twenties with gait disturbances, distal muscle weakness, paresthesias of the lower limbs, and decreased sensation. Bilateral ptosis and ophthalmoplegia were present in both sibs, and the brother also had progressive hearing loss and urinary and erectile dysfunction. Sural nerve biopsy showed loss of myelinated fibers and axonal degeneration without regeneration. Compound heterozygosity for 2 mutations in the POLG gene (174763.0009; 174763.0010) were found in both patients. Spinocerebellar Ataxia with Epilepsy Winterthun et al. (2005) reported 4 unrelated families with a recessively inherited ataxia syndrome characterized by onset of headaches and/or seizures in childhood or adolescence (range 5 to 17 years). By their twenties, all patients developed cerebellar and sensory ataxia, dysarthria, progressive external ophthalmoplegia, and myoclonus. Three patients developed status epilepticus, which was fatal in 1. Several patients showed MRI signal abnormalities deep in the cerebellum and in the thalamus. Muscle biopsies in most patients showed COX-negative fibers, and mtDNA deletions were found in all patients. Affected members from 2 families were homozygous for the same POLG mutation (A467T; 174763.0002), and patients from the remaining 2 families were compound heterozygous for 2 POLG mutations (174763.0013 and 174763.0016). Winterthun et al. (2005) emphasized that migraine, seizures, and myoclonus were especially frequent in this group of patients. Hakonen et al. (2005) referred to this disorder as 'mitochondrial spinocerebellar ataxia-epilepsy syndrome' (MSCAE) or 'mitochondrial recessive ataxia syndrome' (MIRAS). | |||||||||||||||||||||||||||
| Molecular Genetics | |||||||||||||||||||||||||||
| In a patient with SANDO, Van Goethem et al. (2003) identified compound heterozygosity for 2 mutations in the POLG gene (174763.0002; 174763.0005). The finding indicated that SANDO is a variant of autosomal recessive PEO. In 3 Finnish sibs with SANDO reported by Rantamaki et al. (2001), Van Goethem et al. (2004) identified a homozygous mutation in the POLG gene (W748S; 174763.0013). Another unrelated Finnish patient had the same homozygous mutation. In 3 affected Belgian patients, 2 of whom were sibs, Van Goethem et al. (2004) identified a homozygous mutation in the POLG gene (A467T; 174763.0002). A British patient with sporadic SANDO was compound heterozygous for the W748S and A467T mutations. Schulte et al. (2009) identified homozygous or compound heterozygous POLG mutations in 9 of 26 patients from 23 families with cerebellar ataxia plus external ophthalmoplegia and/or sensory neuropathy. Two additional patients from this cohort had heterozygous POLG mutations, consistent with PEOA1. Noting that the molecular diagnosis of cerebellar ataxia can be difficult, Schulte et al. (2009) found that for POLG-associated ataxia, the additional presence of ophthalmoplegia had a predictive value of 80%, whereas the presence of neuropathy had a predictive value of 45%. | |||||||||||||||||||||||||||
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