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What is nemaline myopathy?


A summary of NM? Scientific website
Wikipedia explanation is much easier to understand


NEMALINE MYOPATHY
Alternate Name: Rod body disease
Age of: Onset: Birth to adulthood

What is nemaline myopathy?
First described in 1963, nemaline myopathy is a disease of voluntary muscle that is often nonprogressive. The most common form of the disease is not fatal, although a rare form of the disorder is. Why is it called nemaline myopathy? Nemaline means threadlike, and researchers chose this name because of the presence in affected muscle cells of threadlike or rod-shaped material. The significance of these rodlike bodies is still not clear.

What are the symptoms of nemaline myopathy?
People with nemaline myopathy have moderate weakness in their leg, arm and trunk muscles, accompanied by some mild weakness of the face, tongue and throat muscles. Reflexes are decreased or absent. Affected children often have long, narrow faces with high-arched palates and slender body musculatures. High-arched feet and curvature of the spine are common, and the jaw may also be malformed. The severest form of nemaline myopathy usually appears at birth. Affected children have a marked weakness and a lack of muscle tone. Their respiratory muscles are weak, and death often occurs in the first few years of life due to respiratory failure.

How are the muscle diseases known as inheritable myopathies inherited?
Most of these myopathies are inherited in an autosomal dominant pattern, which means that a child need only inherit the defective gene from one parent in order to have the disease. The parent transmitting the gene also has the disorder, and each of his or her children has a 50 percent chance of inheriting the disease. Autosomal refers to the fact that the genetic defect may be located on any of the 46 rodlike structures, called chromosomes, that hold the genes found in each human cell, except the two that determine a person's sex. With an autosomal inheritance pattern, male and female children are equally affected. In rare instances, some forms of these diseases appear to follow an autosomal recessive pattern or an X-linked recessive pattern. A disease governed by the recessive pattern requires that both parents, who usually do not have the disease, pass on the defective gene in order for a child to be affected by the disease. Each child of such parents has a 25 percent chance of inheriting and showing signs of the disease. A 50 percent chance exists that such a child will inherit the defective gene from only one parent and, therefore, will be a carrier of the flawed gene and will usually not show signs of the disease. X-linked refers to a gene that is on the X chromosome, which along with the Y chromosome determines sex. Male children have one X chromosome and one Y chromosome, while females have two X chromosomes. Therefore, inheritance
of a gene on the X chromosome is different from that for one on an autosomal chromosome. In the X-linked recessive pattern, the disease develops mostly in males. Females who inherit the defective gene are usually carriers like their mothers and can pass the disease on to their sons but rarely show signs of the disease themselves. Central core disease, some forms of myotonia congenita, myotubular myopathy (possibly), some forms of nemaline myopathy, paramyotonia congenita and periodic paralysis follow the autosomal dominant pattern. One form of myotonia congenita and some forms of nemaline myopathy follow the autosomal recessive pattern. Some forms of myotubular myopathy follow the X-linked recessive pattern.

Other Myopathies:
This is a group of un-related genetic muscle disorders, usually named for peculiarities seen in biopsies of muscle tissue. Central core disease, usually apparent at birth, causes skeletal deformities and diffuse weakness. Nemaline myopathy, also usually apparent at birth, results in loss of muscle tone and progressive weakness in limb and trunk muscles. Myotubular myopathy causes poor muscle tone at birth and varying degrees of weakness in eye, facial, neck and limb muscles.


DOMINANT & RECESSIVE - The Simple Explanation

We all have two set of chromosomes (with all the various genes) - one set from mom and the second set from dad. The sex chromosomes X and Y define our sex - XX for girls, XY for boys. The rest of the chromosomes (# 1 to 22) are called autosomes (hence where the term autosomal comes from). We each have two sets of the autosomal chromosomes (# 1 to 22) which means that we also have TWO COPIES of EACH GENE.

When a genetic condition is AUTOSOMAL DOMINANT, one of the genes is not working right, and the gene that is "ok" cannot compensate for the affected gene. Some types of NM are autosomal dominant.
With an autosomal dominant condition, the next generation has a 50% chance of receiving the affected gene from the affected parent.

When a genetic condition is AUTOSOMAL RECESSIVE, both of the genes are not working right. Other types of NM are autosomal recessive.
Children who show the recessive condition have inherited one affected gene from mom and one affected gene from dad. Parents of the affected child are carriers - they have one gene that is "ok", and the other gene is not working right. In this case the "ok" gene can compensate for the affected gene, and the carrier does not show signs of the condition. There is a 25% chance of the next generation getting both affected genes from two carrier parents.
If the affected children then go on to have kids with a partner that has both copies of the gene being "ok" - the next generation will be carriers - get the affected gene from the affected parent and an "ok" gene from the partner.
For families with more than one NM child and no prior history, autosomal recessive is the given explanation. However, genetics is not always this straightforward and there are more complex possibilities which will give a different outcome in the subsequent generation - why more research needs to be done .......

By Daphne
(proud mother of two great kids, Taryn and Keelan, both with NM and no prior family history of NM - note how we didn't follow the 25% genetic rule!)



Forms of
nemaline myopathy
NM is a rare genetic neuromuscular disorder which was first described in 1963. A Finnish study in 1997 gave an estimated incidence of NM at just
1 in 50,000. This figure is based on a small population and may not be applicable worldwide. The severity of this disease varies greatly.
Research suggests five subgroups;
1) Severe form in newborns
2) Typical form
3) Benign congenital form
4) Adult onset
5) Childhood or juvenile onset
The histological definition is the presence of thread-like or rod bodies in the fibres of muscles.



Symptoms of nemaline myopathy
It has been shown that each individual with NM does not always present all the symptoms in their group. Some people develop symptoms later.
Some symptoms are found in more than one form of NM.

Severe infant form:
Common symptoms: Breathing difficulties, poor or no sucking, reflux, high arched palate, low muscle tone, floppy limbs.
Less common: club feet.
Look out for: scoliosis, kyphosis, cronic ear infections (tubes often needed)
Recommended: annual sleep study, swallow study/study of aspiration, nutritionist workup
cranial/facial follow-up, endocrine work-up, baseline cardiologist work-up and follow-up every 6 months.

Typical form: (Can stay mildly affected, or become weaker)
Common symptoms: low muscle tone, high arched palate, delayed motor skills development,.
Less common: occassional shaking/trembling hands.
Look out for: scoliosis, kyphosis
Recommended: annual sleep study, and regular exercise.

Childhood form: (Can stay mildly affected, or become weaker)
Common symptoms: weakening of respiratory system, low muscle tone, high arched palate.
Look out for: scoliosis, kyphosis, delayed motor skills development
Recommended: annual sleep study, and regular exercise.

Adult onset form, aka Sporadic Late Onset Nemaline Myopathy: ( Can appear from 30's, but mostly 50's onwards.)
Common symptoms: respiratory weakening, general weakness in limbs
Onset can be fairly quick, over a couple of years.
Less common: constant pain in limbs
Look out for: losing balance, tripping up
Recommended: annual sleep study
Treatment of IVIG infusion can relieve symptoms and give some strength back.
This is considered by researchers to be a different disorder. It is thought SLONM is not genetic, but rather an "aquired" disorder.


Myopathy vs Dystrophy

A myopathy is any disease of the muscle (myo=muscle; pathos=disease). A dystrophy is actually a class of myopathy that is characterized by progressive muscle degeneration. Nemaline myopathy is known as a non- dystrophic myopathy because muscle biopsies of patients with dystrophies look different under the microscope and because NM is often non-progressive. It's easy to confuse the word myopathy with dystrophy: both words refer to diseases that affect skeletal muscle, which is the type of muscle that is responsible for movement and force.


This page was last updated: October 22, 2014
© David McDougall. 1999-2014
Contact: davidmcd_@hotmail.com