Muscle Biomarkers Correlate With Severity in SBMA

Neurofilament Light Chain [NfL]

Image: BestPractice

Wikipedia describes Neurofilaments this way: NF are intermediate filaments found in the cytoplasm of neurons. They are protein polymers measuring approximately 10 nm in diameter and many micrometers in length. Together with microtubules and microfilaments, they form the neuronal cytoskeleton. They are believed to function primarily to provide structural support for axons and to regulate axon diameter, which influences nerve conduction velocity. Neurofilaments are found in vertebrate neurons in especially high concentrations in axons, where they are all aligned in parallel along the long axis of the axon forming a continuously overlapping array. In addition to their structural role in axons, neurofilaments are also cargoes of axonal transport. Most of the neurofilament proteins in axons are synthesized in the nerve cell body, where they rapidly assemble into neurofilament polymers within about 30 minutes. These assembled neurofilament polymers are transported along the axon on microtubule tracks powered by microtubule motor proteins. 

Below is a portion of the abstract from a study published February 20th. You can read the entire study (PDF) at Neurology.org . 

Muscle and not neuronal biomarkers correlate with severity in spinal and bulbar muscular atrophy

Objective: To determine whether blood biomarkers of neuronal damage (neurofilament light chain [NfL]), muscle damage (creatine kinase [CK]), and muscle mass (creatinine) are altered in spinal bulbar muscular atrophy (SBMA aka Kennedy's Disease) and can be used as biomarkers for disease severity.

Methods: In this multicenter longitudinal prospective study, plasma and serum were collected from 2 cohorts of patients with SBMA in London, United Kingdom (n = 50), and Padova, Italy (n = 43), along with disease (amyotrophic lateral sclerosis [ALS]) and healthy controls, and levels of plasma and serum NfL, CK, and creatinine were measured. Disease severity was assessed by the SBMA Functional Rating Scale and the Adult Myopathy Assessment Tool at baseline and 12 and 24 months.

Results: Blood NfL concentrations were increased in ALS samples, but were unchanged in both SBMA cohorts, were stable after 12 and 24 months, and were not correlated with clinical severity. Normal NfL levels were also found in a well-established mouse model of SBMA. Conversely, CK concentrations were significantly raised in SBMA compared with ALS samples, and were not correlated to the clinical measures. Creatinine concentrations were significantly reduced in SBMA, and strongly and significantly correlated with disease severity.

Conclusions: While muscle damage and muscle mass biomarkers are abnormal in SBMA, axonal damage markers are unchanged, highlighting the relevant primary role of skeletal muscle in disease pathogenesis. Creatinine, but not CK, correlated with disease severity, confirming its role as a valuable biomarker in SBMA.

Note: The KDA just posted the research on their website. There was also a note from Pietro Fratta, who spoke about his biomarker research at last year's conference:

This work uses blood samples from 93 Kennedy’s patients, alongside controls and samples from models of disease, to look for traces of neuron and muscle damage in Kennedy’s disease. It finds that muscle damage is prominent, whilst neuron damage is below detection levels. This work highlights the role of muscle damage in Kennedy’s disease, which is extremely important for how therapies are designed. Further, this study supports the use of a specific biomarker, creatinine, for Kennedy’s disease clinical trials.

This study was possible only thanks to the incredibly strong participation to research of patients attending the Kennedy’s Clinic at the National Hospital in London and the University of Padova.