Leukoencephalopathy With Brainstem And Spinal Cord Involvement And Lactate Elevation

A number sign (#) is used with this entry because of evidence that leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) can be caused by homozygous or compound heterozygous mutation in the gene encoding mitochondrial aspartyl-tRNA synthetase (DARS2; 610956) on chromosome 1q25.

Description

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is defined on the basis of a highly characteristic constellation of abnormalities observed by magnetic resonance imaging and spectroscopy (Scheper et al., 2007). Affected individuals develop slowly progressive cerebellar ataxia, spasticity, and dorsal column dysfunction, sometimes with a mild cognitive deficit or decline.

Clinical Features

A novel leukoencephalopathy with brainstem and spinal cord involvement and high lactate was described by van der Knaap et al. (2002) in 8 patients. They showed a distinct magnetic resonance spectroscopy (MRS) pattern of inhomogeneous cerebral white matter abnormalities and selective involvement of brainstem and spinal tracts. Proton magnetic resonance imaging (MRI) showed increased lactate in the abnormal white matter. Clinically, the patients had slowly progressive pyramidal, cerebellar, and dorsal column dysfunction. Autosomal recessive inheritance was considered likely. Three of the 8 patients were male. The 8 patients included 2 affected sisters and an affected brother and sister.

Linnankivi et al. (2004) described 5 additional patients with this entity. MRS showed decreased N-acetylaspartate and increased lactate in the white matter of all patients. A slowly progressive sensory ataxia and tremor manifested at the age of 3 to 16 years and distal spasticity in adolescence. One 13-year-old patient was asymptomatic. Two of the 5 patients were brothers.

Serkov et al. (2004) also described 5 new, unrelated patients. The clinical picture was homogeneous with onset in childhood, a slowly progressive course, variable mental deficits, signs of pyramidal and cerebellar dysfunction, and sometimes dorsal column dysfunction. Serkov et al. (2004) proposed the acronym LBSL for leukoencephalopathy with involvement of brainstem and spinal cord and increased lactate.

Petzold et al. (2006) described sister and brother with adult-onset leukoencephalopathy with brainstem and spinal cord involvement and normal lactate on MRS. Onset had occurred at ages 20 years in the sister and 23 years in the brother with unsteady gait, stiffness in both legs, and bilateral clumsiness. The parents were not consanguineous.

Isohanni et al. (2010) reviewed the clinical features of 5 patients with LBSL reported by Linnankivi et al. (2004) and described 3 new patients. Six patients were of Finnish origin. Overall, the phenotype was somewhat heterogeneous, with most patients showing onset between ages 2 to 15 years. Most had unsteady or delayed motor development, but 2 had normal motor development. The most common features included progressive onset of tremor, ataxia, dysarthria, and spasticity. A novel finding was an axonal peripheral neuropathy with distal weakness and decreased vibration/proprioception. Four patients had normal cognitive function, and 4 had mild defects of speech, learning problems, or visuospatial defects. Two patients were described in detail. One had onset at age 8 years with nocturnal seizures and was found to have abnormalities in the infra- and supratentorial regions on brain MRI. At age 15 years, he developed ataxia, extensor plantar responses, spasticity, and an axonal neuropathy. The other patient had onset at age 19 months of motor delay with ataxia and hypotonia. Spasticity and hyperreflexia became apparent by age 2 years, 3 months. He also had mild speech delay. Brain MRI showed abnormal signals in the supratentorial region. All patients were compound heterozygous for mutations in the DARS2 gene, and Isohanni et al. (2010) suggested that homozygosity for a DARS2 mutation may be lethal in humans.

Miyake et al. (2011) reported 3 Japanese sibs, born of consanguineous parents, with a severe form of LBSL due to a homozygous mutation in the DARS2 gene (610956.0012). The 21-year-old proband developed truncal ataxia at age 3 years, followed by nystagmus, slurred speech, tremor, muscle tonus abnormality, and mental retardation; he could speak only 1 or 2 words. Other features in the proband included peripheral muscle atrophy and weakness, joint contractures, hyporeflexia, and disrupted deep sensation. His 2 sibs, who showed onset before age 12 months, died in childhood of respiratory disease. Brain imaging showed leukoencephalopathy of the cerebrum, cerebellum, brainstem, and spinal cord. The wildtype DARS2 mRNA transcript and protein were significantly decreased in patient cells. Miyake et al. (2011) noted that homozygosity for pathogenic mutations in the DARS2 gene had not previously been reported.

Clinical Variability

Synofzik et al. (2011) reported a 25-year-old German woman who presented with a 3-year history of paroxysmal exercise-induced gait ataxia. The episodic ataxia occurred up to 5 times a day and lasted for a few seconds to 5 minutes, but the frequency increased to up to 23 times per day over a few years. Other features included mild distal deficits in position and vibration sense, mild leg spasticity, and hyperreflexia, but she never had permanent cerebellar ataxia or gait spasticity. Serum lactate was intermittently increased, and brain MRI showed T2 hyperintense lesions in the cerebellar white matter, deep cerebral white matter, and periventricular region, with some involvement of the pyramidal tracts and dorsal columns. Treatment with acetazolamide resulted in significantly decreased frequency of the attacks. Genetic analysis identified a homozygous mutation in the DARS2 gene (R609W; 610956.0013) and excluded mutations in known episodic ataxia genes. The findings indicated that this disorder can have a milder phenotype and even present with episodic ataxia.

Mapping

Scheper et al. (2007) performed linkage mapping with microsatellite markers in LBSL families and found a candidate region on chromosome 1, which they narrowed to a 1.9-cM region between markers D1S2790 and D1S416 by means of shared haplotypes.

Molecular Genetics

Scheper et al. (2007) sequenced genes in the candidate region on chromosome 1 linked to LBSL and uncovered mutations in DARS2 (610956), which encodes mitochondrial aspartyl-tRNA synthetase, in affected individuals from all 30 families. Enzyme activities of mutant proteins were decreased. Surprisingly, activities of mitochondrial complexes from fibroblasts and lymphoblasts derived from affected individuals were normal, as determined by different assays.

Inheritance

Van der Knaap et al. (2002) postulated autosomal recessive inheritance of LBSL based on the presence of 2 affected sib pairs among their patients. Linnankivi et al. (2004), Serkov et al. (2004), and Petzold et al. (2006) likewise thought autosomal recessive inheritance likely Scheper et al. (2007) proved this to be the case, with affected individuals carrying mutations on both alleles of the DARS2 gene.