Unraveling LBSL: When Family Genes Tell Different Stories
"A Sudanese family's case sheds light on the unpredictable nature of DARS2-related leukoencephalopathy and the importance of genetic screening."
Imagine a disease where the blueprint of your body – your genes – holds the key, yet the story they tell varies dramatically from person to person, even within the same family. This is the reality of Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation, or LBSL. LBSL (OMIM #611105) is a rare genetic disorder affecting the central nervous system. It's characterized by progressive damage to the brain's white matter, brainstem, and spinal cord, often accompanied by elevated levels of lactate, a chemical compound involved in energy production.
LBSL stems from mutations in the DARS2 gene, responsible for producing an enzyme crucial for mitochondrial function. Mitochondria are the powerhouses of our cells, and when DARS2 malfunctions, these powerhouses falter, leading to a cascade of neurological problems. While the genetic cause is singular, the presentation of LBSL is anything but uniform. Symptoms can range from mild motor impairments to severe disability, with onset occurring anywhere from early childhood to adulthood.
A recent case study from a Sudanese family, published in BMC Neurology, highlights this remarkable variability. The study, led by Ashraf Yahia and colleagues, details the experiences of two siblings diagnosed with LBSL and their elder sister, all carrying the same DARS2 mutations. Their story underscores the complexities of LBSL, the importance of considering genetic screening even in seemingly healthy individuals, and the challenges of predicting the course of this rare condition.
LBSL Research and Diagnosis
LBSL is regarded as a relatively mild leukodystrophy and is associated with characteristic long-tract abnormalities on MRI and biallelic variants in DARS2. Diagnosis involves clinical evaluation, patient history, specialized testing, and genetic testing for DARS2 mutations. The Moser Center's 2023 research report described encouraging results from gene-therapy experiments involving the gene that causes LBSL, while its 2024 report described AAV9 delivery of the full-length healthy DARS2 gene in mice and patient cells.
Screening Methods and Practical Limits
Genomic screening involves technical and logistical approaches used by clinical genetics programs, including work represented by Baylor College of Medicine and Baylor Genetics. Newborn screening historically used the heel-prick test to identify phenylketonuria soon after birth, allowing affected babies to begin a low-phenylalanine diet before intellectual disability, seizures, and behavioral problems developed. However, real-world screening can fall short of guidelines, as reported for Lynch syndrome screening in a public cancer center, and laboratory practice requires quality recommendations for professionals, service users, and newborn-screening systems.
From Heel Pricks to Genomic Screening
Newborn screening developed as a public-health system for identifying treatable conditions before symptoms appear. In the United States, dried blood spot cards are obtained within the first 24 to 48 hours of life, while point-of-care testing helps detect hearing loss and critical congenital heart disease. In 2002, the Maternal and Child Health Bureau asked the American College of Medical Genetics to develop screening guidelines; its review of 81 conditions produced a core panel of 29.
A Family's Tale: Different Faces of the Same Mutation
The Sudanese family presented a unique puzzle for doctors. Two siblings, aged 18 and 15, exhibited classic LBSL symptoms since infancy: pyramidal signs (indicating motor pathway damage) and developmental delays. Genetic testing confirmed they both carried two compound heterozygous variants in the DARS2 gene (NM_018122.4:c.1762C > G and c.563G > A), meaning they inherited a different mutated copy of the gene from each parent.
- The Affected Siblings: Displayed delayed motor development, speech difficulties, and seizures (in one case). They experienced progressive spasticity, requiring support for walking, and exhibited ocular cerebellar signs like nystagmus.
- The Minimally Affected Sister: Showed only subtle signs on physical examination, with no functional impairments. She had normal cognitive function and attended university.
- A Surprising Twist: Despite the elder sister's mild clinical presentation, brain MRI scans revealed abnormalities similar to her affected siblings, including high signal intensity in the periventricular white matter and dentate nuclei. Furthermore, her serum lactate levels were also elevated, comparable to those of her ill sisters.
Expanding the LBSL Evidence Base
A 2026 review identified 899 patients with 19 different mitochondrial aminoacyl-tRNA synthetase deficiencies. Across those deficiencies, age at presentation ranged from 0 to 63 years, and reported death rates ranged from 0% to 57%. A separate case report states that mutations in the DARS2 gene cause LBSL, while a study of Sudanese families reached a genetic diagnosis in 63% of families and possibly up to 73% when variants of unknown significance were considered.
Why Genetic Results Need Context
A case report of a Sudanese family with DARS2-related LBSL described the variant c.563G > A, also known as rs182811621, as absent from ClinVar at the time reported. The variant had very low allele frequencies in the ExAC and gnomAD databases, listed as 0.00001 and 0.000004, respectively. Genetic testing also has broader limitations: MedlinePlus notes that physical risks are generally very small for blood or buccal-smear tests, while results can still require careful interpretation and may not provide certainty about disease.
Variants, Testing, and Care
A report on LBSL found the c.492 + 2 T > C mutation in Patients 1 and 2. This intron 5 defect causes exon skipping without a frameshift and was described as the most common pathogenic variant reported in LBSL. Comparative care resources emphasize that LBSL management also involves genetic-testing information, MRI and lactate-test limitations, supportive treatment, and precautions related to head injury.
Implications and Future Directions
The Sudanese family's story underscores the importance of considering genetic screening for LBSL, even in individuals who appear relatively healthy. Identifying asymptomatic or minimally symptomatic carriers is particularly relevant in communities where consanguineous marriage (marriage between closely related individuals) is common, as it increases the risk of inheriting recessive genetic disorders like LBSL.
Testing in Clinical Context
Clinical molecular testing for LBSL can use sequence analysis of the entire coding region through next-generation sequencing or massively parallel sequencing. The Genetic Testing Registry lists this type of test for leukoencephalopathy with brain stem and spinal cord involvement-high lactate syndrome. LBSL is characterized by slowly progressive cerebellar ataxia and spasticity with dorsal-column dysfunction in most individuals, with neurologic dysfunction affecting the legs more than the arms.
The Changing Genetic-Testing Landscape
Grand View Research's Genetic Testing Market report describes trends and future outlook across more than 20 countries. Its coverage includes government initiatives, the funding landscape, competitive strategies, and existing competition. Other forward-looking sources identify next-generation sequencing and non-invasive prenatal testing as important developments, while Avalon’s 2026 Lab Trend Report highlights AI, liquid biopsy, blood biomarkers, and direct-to-consumer testing as innovations affecting precision medicine.
Consent and Family Participation
The Crossref record for a published case report states that written informed consent was obtained from fathers for participants younger than 18. It also records that participants signed informed consents for publication of personal and medical details included in the case report. These details illustrate the ethical role of patients and families in allowing rare-disease experiences to be documented and shared.
The study also highlights the need for further research to understand the factors that contribute to the variable expressivity of LBSL. Why do some individuals with DARS2 mutations develop severe symptoms, while others remain largely unaffected? Potential explanations include other genetic modifiers, environmental factors, or differences in mitochondrial function.
Ultimately, unraveling the complexities of LBSL's phenotypic variability will pave the way for more accurate diagnoses, improved genetic counseling, and potentially, targeted therapies that can address the underlying mechanisms of this challenging neurological disorder. Further functional studies are needed to confirm the pathogenicity of the reported variants. This report is the first to report cases of LBSL from sub-Saharan Africa.