What is HIBM or GNE Myopathy?

Hereditary Inclusion Body Myopathies (HIBM) are a group of muscle wasting disorders, which are uncommon in the general world population. An autosomal recessive form of HIBM is known as GNE Myopathy, IBM2, which is a common genetic disorder amongst people of Iranian-Jewish descent. IBM2 has also been identified in other minorities throughout the world. Patients of Asian (Japanese and others), European, and South American origin, as well as Muslim patients in the Middle Eastern, Palestinian, and Iranian origin, have been identified. In Japan and many East Asian countries, this disorder is known as Distal Myopathy with Rimmed Vacuoles (DMRV). More recently, this disorder is called “GNE Myopathy” because it is caused by mutations on the GNE gene leading to hypomorphic key enzyme of sialic acid biosynthesis.

GNE Myopathy causes progressive muscle weakness and wasting. Muscle wasting usually starts around the age of 20 - 30 years, although we have seen young onset at 17 and old onset at 52. As such, it affects the most productive times of our lives. It can progress to marked disability within 10 - 15 years, confining many patients to the wheelchair. The weakness and severity can vary from person to person. In some, weakness in the legs is noticed first. In few others, the hands are weakened more rapidly than the legs. Weakness is progressive, which means the muscle become weaker over time. GNE Myopathy does not seem to affect the brain, internal organs or sensation. The quadriceps are relatively spared, and remain strong until the late stages of disease, which is the reason IBM2 is often referred to as Quadriceps Sparing Myopathy (QSM).

Some early signs of HIBM include:

  • Difficulty walking on heels, and difficulty running;
  • Weak index finger;
  • Frequent loss of balance.

On muscle biopsy, the typical finding includes inclusion bodies, rimmed vacuoles and accumulation of aberrant proteins similar to those found in senile plaques of Alzheimer's Brain disease (amyloid beta, hyperphosphorylated tau, amongst others).

The most useful information for accurate diagnosis is the symptoms and weakness pattern. If the quadriceps are spared but the hamstrings and iliopsoas are severely affected in a person between ages of 20 - 40, it is very likely HIBM will be at the top of the differential diagnosis. The doctor may order any or all of the following tests to ascertain if a patient has IBM2:

  • Blood test for serum Creatine Kinase (CK or CPK);
  • Nerve Conduction Study (NCS) / Electomyography (EMG);
  • Muscle Biopsy;
  • Magnetic Resonance Imaging (MRI) or Computer Tomography (CT) Scan to determine true sparing of quadriceps;
  • Blood Test or Buccal Swab for genetic testing;

This disorder is formally classified on Mendelian Inheritance in Man (MIM) as IBM2 or DMRV. You can reach the online description of this disorder at OMIM:600737(IBM2) or OMIM:605820(DMRV).

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