Hereditary motor and sensory neuropathy, Okinawa type

What it is

From: Orphanet

Hereditary motor and sensory neuropathy, Okinawa type is a rare, genetic, axonal hereditary motor and sensory neuropathy characterized by the adult-onset of slowly progressive, symmetric, proximal dominant muscle weakness and atrophy, painful muscle cramps, fasciculations and distal sensory impairment, mostly (but not exclusively) in individuals (and their descendents) from the Okinawa region in Japan. Absent deep tendon reflexes, elevated creatine kinase levels and autosomal dominant inheritance are also characteristic.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal peripheral action potential amplitude · Very frequent (99-80%)

An anomaly in the magnitude of the action potential along a peripheral nerve, that is, of the rapid rise and fall of the electrical membrane potential of the nerve.

Areflexia · Very frequent (99-80%)

Absence of neurologic reflexes such as the knee-jerk reaction.

Cough · Very frequent (99-80%)

A sudden, audible expulsion of air from the lungs through a partially closed glottis, preceded by inhalation.

Fatiguable weakness of proximal limb muscles · Very frequent (99-80%)

A type of weakness of a skeletal muscle of proximal part of a limb that occurs after a muscle group is used and lessens if the muscle group has some rest. That is, there is diminution of strength with repetitive muscle actions.

Intermittent painful muscle spasms · Very frequent (99-80%)

History of repeated intermittent involuntary muscle contractions that were painful.

Lower limb muscle weakness · Very frequent (99-80%)

Weakness of the muscles of the legs.

Somatic sensory dysfunction · Very frequent (99-80%)

An abnormality of the primary sensation that is mediated by peripheral nerves (pain, temperature, touch, vibration, joint position). The word hypoesthesia (or hypesthesia) refers to a reduction in cutaneous sensation to a specific type of testing.

Upper limb muscle weakness · Very frequent (99-80%)

Weakness of the muscles of the arms.

Abnormal cranial nerve physiology · Frequent (79-30%)

A functional abnormality affecting one or more of the cranial nerves, which emerge directly from the brain stem.

Abnormality of the urinary system · Frequent (79-30%)

An abnormality of the urinary system.

Distal sensory impairment · Frequent (79-30%)

An abnormal reduction in sensation in the distal portions of the extremities.

EMG: positive sharp waves · Frequent (79-30%)

These are spontaneous firing action potentials stimulated by needle movement of an injured muscle fiber. There is propagation to, but not past, the needle tip. This inhibits the display of the negative deflection of the waveform.

Elevated circulating creatine kinase concentration · Frequent (79-30%)

The activity of creatine kinase in the blood circulation is above the upper limit of normal.

Inability to walk · Frequent (79-30%)

Incapability to ambulate.

Other findings in the same source

From: Orphanet

Additional reported features include Limb fasciculations (Frequent (79-30%)); Muscle fibrillation (Frequent (79-30%)); Tremor (Frequent (79-30%)); Bulbar signs (Frequent (79-30%)); Difficulty standing (Frequent (79-30%)); Abnormal glucose homeostasis (Occasional (29-5%)); Abnormality of the seventh cranial nerve (Occasional (29-5%)); Aspiration pneumonia (Occasional (29-5%)); Dysphagia (Occasional (29-5%)); Dyspnea (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

When it may begin

From: Orphanet

Adult

Inheritance in the source

From: Orphanet

Autosomal dominant

Frequency and the population described

From: Orphanet

Reported case(s): 120.0; Worldwide. This is a published case count, not prevalence. Point prevalence: Unknown; Worldwide; Class only.

Understanding the inheritance label

From: MedlinePlus Genetics

An autosomal dominant pattern means that one altered copy of a relevant gene can be sufficient for the condition. Some affected people inherit the change; others have a new change without an affected parent. The precise finding, family history and condition determine what this means for relatives.

Which doctor should you see?

The suggested department for discussing Hereditary motor and sensory neuropathy, Okinawa type is Neurology, with a neurologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which nervous-system findings help explain the symptoms?
• Would an assessment of walking, communication or daily function be helpful?
• Are rehabilitation or other specialist services relevant?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Hereditary motor and sensory neuropathy, Okinawa type. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.