Dysferlinopathy in a Cohort of Chinese Patients: Clinical Features, Mutation Spectrum, and Imaging Findings
If two siblings inherit the same genetic mutation for a muscular dystrophy, would they experience the same symptoms? A 2021 study of Chinese patients with dysferlinopathy—an inherited muscle disorder—says no. Not only do genetic differences between populations shape how the disease manifests, but even family members with identical or similar mutations can have wildly different experiences of the same condition.
Researchers from the First Affiliated Hospital of Fujian Medical University and Fujian Key Laboratory of Molecular Neurology analyzed data from 28 patients across 23 families to unpack these complexities. Their work, published in the Chinese Medical Journal, combines genetic testing, clinical exams, and muscle imaging to reveal how mutations in the DYSF gene—responsible for dysferlinopathy—affect people in southern China.
What Is Dysferlinopathy?
Dysferlinopathy is a group of autosomal recessive muscular dystrophies (meaning two faulty DYSF genes—one from each parent—are required to develop the condition). It includes three main subtypes:
- Miyoshi myopathy (MM): Starts with weakness in the lower legs (calves) and spreads to the hips over time.
- Limb-girdle muscular dystrophy type 2B (LGMD2B): Begins with weakness in the hips and thighs (proximal muscles).
- Proximo-distal (PD) phenotype: Affects both proximal (hip/thigh) and distal (calf/ankle) muscles early on.
For years, scientists have struggled to link specific DYSF mutations to exact symptoms—partly because rare “atypical” cases and family-to-family variability complicate the picture. This study aims to fill that gap for Chinese patients.
How the Study Was Done
The team used two advanced genetic tests—targeted next-generation sequencing (NGS) and multiplex ligation-dependent probe amplification—to identify DYSF mutations. They also reviewed:
- Clinical data: Age at symptom onset, muscle weakness patterns, and disease progression.
- Muscle MRI: To track fat infiltration (a marker of muscle damage) in the lower limbs.
All procedures followed the 1964 Declaration of Helsinki and the hospital’s ethical guidelines, and patients provided informed consent.
Key Findings: Mutations Unique to Chinese Patients
The researchers found 26 different DYSF mutations—half of which were new to science. Ten of these novel mutations were pathogenic (directly causing disease), and three were likely pathogenic.
The most common mutation was c.1667T>C (p.L556P), found in 19.6% of alleles across five unrelated families. Haplotype analysis (which tracks genetic inheritance patterns) suggested this mutation is a founder mutation—meaning it originated in a common ancestor and is unique to southern Chinese populations. Another mutation, c.836A>T, was also only seen in Chinese patients.
Notably, four mutations common in Japanese dysferlinopathy patients were not found in this cohort. This aligns with a 2016 study suggesting a different founder mutation (c.1375dupA) in northern China—highlighting regional genetic differences within the country.
Symptoms Vary by Mutation and Subtype
Of the 28 patients:
- 11 had MM (started with calf weakness at an average age of 18 years).
- 13 had LGMD2B (started with hip/thigh weakness at an average age of 25 years).
- 4 had the PD phenotype (mixed proximal/distal weakness).
Patients with the c.1667T>C mutation had a later onset (average 27.5 years) than those without it (19.6 years)—a statistically significant difference. MM patients were also more likely to have only lower limb involvement (8 of 11) compared to LGMD2B patients (3 of 13).
Even Family Members Can Have Different Symptoms
Two families showed striking intra-familial variability—meaning relatives with the same or similar mutations had different symptoms:
- Family 3: A brother with MM started with calf weakness that spread to his hips over three years. His sister, with the same c.1667T>C mutation, had LGMD2B—she first noticed trouble running and had mild hip weakness.
- Family 23: Two relatives had different mutations and phenotypes. One had the PD phenotype (compound heterozygous mutations: c.1644delA and c.5828_5843delCCTTGGACCAGCTGGA), while another had MM (homozygous c.1644delA mutation).
These cases confirm that genetics alone don’t determine how dysferlinopathy plays out—environmental factors or “modifier genes” (which affect how main disease genes work) likely play a role.
Imaging Reveals Pattern of Muscle Damage
Muscle MRI of 22 patients showed clear patterns of damage:
- Thighs: The back muscles (hamstrings: semimembranosus, semitendinosus, biceps femoris) and outer quadriceps (vastus lateralis) were most commonly affected. Front thigh muscles (rectus femoris) were only damaged in advanced stages.
- Lower legs: The calf muscles (soleus, gastrocnemius medialis/lateralis) had the most severe fat infiltration—over 80% of patients showed significant damage here.
The posterior (back) compartments of both the thigh and lower leg were consistently hit hardest, which aligns with how MM and LGMD2B progress.
Why Mutations Matter: Protein Structure and Function
Most novel mutations affected two critical parts of the dysferlin protein:
- C2 domains: These highly conserved regions bind calcium and phospholipids, helping repair muscle cell membranes. Mutations here disrupt this process.
- DysF domains: These maintain protein stability. Mutations here break down “arginine/tryptophan (R/W) stacks”—structures that keep the protein folded—leading to dysferlin degradation.
In short: Mutations in these regions cripple the dysferlin protein, leaving muscles vulnerable to damage over time.
What This Means for Patients and Science
This study expands our understanding of dysferlinopathy in Chinese populations by:
- Identifying 13 novel DYSF mutations and a founder mutation unique to southern China.
- Showing that c.1667T>C is linked to later disease onset—a key clue for genotype-phenotype correlations.
- Highlighting that even family members with the same mutations can have different symptoms—pointing to the need for personalized care.
For clinicians, these findings can help diagnose dysferlinopathy earlier in Chinese patients (especially those with the c.1667T>C mutation) and tailor treatment plans to their specific muscle damage patterns. For scientists, the study underscores how genetic diversity across populations shapes rare diseases—and why “one-size-fits-all” research isn’t enough.
The study, Dysferlinopathy in a Cohort of Chinese Patients: Clinical Features, Mutation Spectrum, and Imaging Findings, was published in the Chinese Medical Journal in 2021 by Qi-Fu Guo, Zhi-Xian Ye, Liang-Liang Qiu, Xin Lin, Jia-He Lai, Min-Ting Lin, Zhi-Qiang Wang, Ning Wang, and Feng Lin.
doi:10.1097/CM9.0000000000001343
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