22 June 2026
: Case report 
Suspected Adult-Onset Congenital Myasthenic Syndrome Associated With a Heterozygous CHRND Variant in a Patient With Seropositive Rheumatoid Arthritis: A Case Report
Challenging differential diagnosis, Congenital defects / diseases
Khaled Abdulwahab Amer
AE 1*, Hanan Hassan Almalki AF 2, Faisal Saud Alhudaithi BD 3
DOI: 10.12659/AJCR.952887
Am J Case Rep 2026; 27:e952887
Table 1 Laboratory investigation findings.
| A: Basic laboratory parameters. | |||
|---|---|---|---|
| Test | Value | Units | Normal range |
| 135.70 | mmol/L | 135–145 | |
| 1.02 | mg/dL | 0.6–1.3 | |
| 20.67 | mg/dL | 7–20 | |
| 3.82 | mmol/L | 3.5–5.1 | |
| 4.26 | g/dL | 3.5–5.0 | |
| 0.00 | mg/dL | 0.0–0.3 | |
| 0.42 | mg/dL | 0.1–1.2 | |
| 63.61 | U/L | 44–147 | |
| 16.26 | U/L | 10–40 | |
| 9.86 | U/L | 7–56 | |
| 6.2 | × 10/μL | 4.0–11.0 | |
| 2.0 | × 10/μL | 1.5–7.5 | |
| 2.8 | × 10/μL | 1.0–4.0 | |
| 0.7 | × 10/μL | 0.2–0.8 | |
| 0.5 | × 10/μL | 0.0–0.5 | |
| 0.1 | × 10/μL | 0.0–0.1 | |
| 32.1 | % | 40–70 | |
| 46.1 | % | 20–45 | |
| 11.8 | % | 2–10 | |
| 8.8 | % | 0–6 | |
| 1.2 | % | 0–1 | |
| 4.95 | × 10/μL | 4.2–5.9 | |
| 13.3 | g/dL | 13.0–17.0 | |
| 41.6 | % | 40–52 | |
| 84.1 | fL | 80–100 | |
| 26.9 | pg | 27–33 | |
| 32.0 | g/dL | 32–36 | |
| 14.2 | % | 11.5–14.5 | |
| 41.6 | fL | 39–46 | |
| 431 | × 10/μL | 150–450 | |
| 8.5 | fL | 7.5–11.5 | |
| Abbreviations: AChR, acetylcholine receptor; ALP, alkaline phosphatase; ALT, alanine aminotransferase; ANA, antinuclear antibody; AST, aspartate aminotransferase; BUN, blood urea nitrogen; CCP, cyclic citrullinated peptide; CV, coefficient of variation; HMG-CoA, 3-hydroxy-3-methylglutaryl coenzyme A; IMNM, immune-mediated necrotizing myopathy; MCH, mean corpuscular hemoglobin; MCHC, mean corpuscular hemoglobin concentration; MCV, mean corpuscular volume; MG, myasthenia gravis; MPV, mean platelet volume; MuSK, muscle-specific kinase; RA, rheumatoid arthritis; RBC, red blood cell; RDW, red cell distribution width; RNP, ribonucleoprotein; SD, standard deviation; WBC, white blood cell. | |||
| B: Immunological and specialized tests. | |||
| Test | Result | Reference range | Interpretation |
| Normal | – | – | |
| Normal | – | No myopathic pattern | |
| 363 U/mL | < 20 U/mL | Positive | |
| Negative | – | Consistent with seropositive RA | |
| Negative | – | – | |
| Negative | – | – | |
| Negative | – | Seropositive MG unlikely | |
| Negative | – | Seropositive MG unlikely | |
| Negative | – | – | |
| Negative | – | No IMNM | |
| Abbreviations: AChR, acetylcholine receptor; ALP, alkaline phosphatase; ALT, alanine aminotransferase; ANA, antinuclear antibody; AST, aspartate aminotransferase; BUN, blood urea nitrogen; CCP, cyclic citrullinated peptide; CV, coefficient of variation; HMG-CoA, 3-hydroxy-3-methylglutaryl coenzyme A; IMNM, immune-mediated necrotizing myopathy; MCH, mean corpuscular hemoglobin; MCHC, mean corpuscular hemoglobin concentration; MCV, mean corpuscular volume; MG, myasthenia gravis; MPV, mean platelet volume; MuSK, muscle-specific kinase; RA, rheumatoid arthritis; RBC, red blood cell; RDW, red cell distribution width; RNP, ribonucleoprotein; SD, standard deviation; WBC, white blood cell. | |||