A case with leukoencephalopathy with brainstem and spinal cord involvement and elevated lactate (LBSL) with Its Characteristic Clinical and Neuroimaging Findings

The Leukodystrophies HBSL and LBSL-Correlates and Distinctions

Aminoacyl-tRNA synthetases (ARSs) accurately charge tRNAs with their respective amino acids. As such, they are vital for the initiation of cytosolic and mitochondrial protein translation. These enzymes have become increasingly scrutinized in recent years for their role in neurodegenerative disorders caused by the mutations of ARS-encoding genes. This review focuses on two such genes-DARS1 and DARS2-which encode cytosolic and mitochondrial aspartyl-tRNA synthetases, and the clinical conditions associated with mutations of these genes. We also describe attempts made at modeling these conditions in mice, which have both yielded important mechanistic insights. Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a disease caused by a range of mutations in the DARS2 gene, initially identified in 2003. Ten years later, hypomyelination with brainstem and spinal cord involvement and leg spasticity (HBSL), caused by mutations of cytosolic DARS1, was discovered. Multiple parallels have been drawn between the two conditions. The Magnetic Resonance Imaging (MRI) patterns are strikingly similar, but still set these two conditions apart from other leukodystrophies. Clinically, both conditions are characterized by lower limb spasticity, often associated with other pyramidal signs. However, perhaps due to earlier detection, a wider range of symptoms, including peripheral neuropathy, as well as visual and hearing changes have been described in LBSL patients. Both HBSL and LBSL are spectrum disorders lacking genotype to phenotype correlation. While the fatal phenotype of Dars1 or Dars2 single gene deletion mouse mutants revealed that the two enzymes lack functional redundancy, further pursuit of disease modeling are required to shed light onto the underlying disease mechanism, and enable examination of experimental treatments, including gene therapies.

Drug Treatment of Epilepsy Neuropsychiatric Comorbidities in Children

There is increasing recognition that epilepsy can be associated with a broad spectrum of comorbidities. While epileptic seizures are an essential element of epilepsy in children, there is a spectrum of neurological, mental health and cognitive disorders that add to the disease burden of childhood epilepsy resulting in a decreased quality of life. The most common comorbid conditions in childhood epilepsy include depression, anxiety, autism spectrum disorders, sleep disorders, attention deficits, cognitive impairment, and migraine. While epilepsy can result in comorbidities, many of the comorbidities of childhood have a bi-directional association, with the comorbid condition increasing risk for epilepsy and epilepsy increasing the risk for the comorbid condition. The bidirectional feature of epilepsy and the comorbidities suggest a common underlying pathological basis for both the seizures and comorbid condition. While recognition of the comorbid conditions of pediatric epilepsies is increasing, there has been a lag in the development of effective therapies partly out of concern that drugs used to treat the comorbid conditions could increase seizure susceptibility. There is now some evidence that most drugs used for comorbid conditions are safe and do not lower seizure threshold. Unfortunately, the evidence showing drugs are effective in treating many of the childhood comorbidities of epilepsy is quite limited. There is a great need for randomized, placebo-controlled drug trials for efficacy and safety in the treatment of comorbidities of childhood epilepsy.

A New DARS2 Mutation Discovered in an Adult Patient

We report a case of an adult patient suffering from leukoencephalopathy with brainstem and spinal cord involvement and elevated white matter lactate (LBSL) caused by a DARS2 polymorphism. DARS2 mutation was identified by combining MRI and genetic analysis. Our patient was affected by compound heterozygosity for a pathogenic mutation and a common variant, but with reduced aspartyl-tRNA synthetase activity. Brain and spinal cord magnetic resonance imaging revealed extensive white matter abnormalities; spectroscopy revealed no lactate elevation. A new compound heterozygous DARS2 variant combined with a polymorphism in the other allele in an adult patient with LBSL was identified, resulting in reduced DARS2 activity. This combination is rare and has consequences on how we should consider benign variant polymorphisms in the future.