Nemaline myopathy

Nemaline myopathy
Classification and external resources
ICD-10	G71.2
ICD-9	359.0
OMIM	161800 256030 605355
DiseasesDB	31991 33448 33447
eMedicine	neuro/76 neuro/230
GeneReviews	Nemaline myopathy

Nemaline myopathy (also called rod myopathy or nemaline rod myopathy) is a congenital, hereditary neuromuscular disorder that causes muscle weakness, generally nonprogressive, of varying severity.

"Myopathy" means "muscle disease," and a biopsy of muscle from a person with nemaline myopathy shows abnormal thread-like^[1] rods, called nemaline bodies, in the muscle cells. People with nemaline myopathy (or NM) usually experience delayed motor development and weakness in the arm, leg, trunk, throat, and face muscles.

The disorder is often clinically categorized into several groups, including mild (typical), intermediate, severe, and adult-onset; however, these distinctions are somewhat ambiguous, as the categories frequently overlap. Respiratory problems are a primary concern for people with all forms of NM, and though in some severe cases they may threaten life expectancy, aggressive and proactive care allows most individuals to survive and lead active lives.

Nemaline myopathy is one of forty neuromuscular diseases covered by the Muscular Dystrophy Association.

Genetic qualities

Nemaline myopathy is a clinically and genetically heterogeneous disorder. Both autosomal dominant and autosomal recessive forms occur. Genetic mutations found to be responsible for the disorder include

Gene	Type	OMIM	Locus	Notes
TPM3	NEM1	609284
NEB	NEM2	256030	2q22
ACTA1	NEM3	161800	1q22-q23, 9p13.2-p13.1, 1q42.1
TPM2	NEM4	609285
TNNT1	NEM5	605355	19q13.4	Also known as Amish nemaline myopathy

The physical capabilities of a given person with NM do not correlate well either with genotype or with muscle pathology as observed in the biopsy.^[2]

History and early identification

"Rod myopathy" was first identified by Dr. Douglas Reye, an Australian physician, in 1958. However, Reye's results were never published because another doctor dismissed his finding of rods in the muscle tissue as an artifact of the biopsy. Forty years later, Reye's "rod myopathy" patient was confirmed to have nemaline myopathy. Another group of Australian researchers has since published an article recognizing Reye for his work.^[3]

"Nemaline myopathy" was first named in a published paper in 1963 by North American researchers Cohen and Shy. Today, laboratories performing research on NM are located in the United States (Boston), Finland, and Australia.

Physical characteristics and effects

Physical expression of nemaline myopathy varies greatly, but weakness is usually concentrated in the proximal muscles, particularly respiratory, bulbar and trunk muscles. People with severe NM are usually obviously affected at birth, while those with intermediate or mild NM may initially appear unaffected. Babies with NM are frequently observed to be "floppy" and hypotonic. Children born with NM often gain strength as they grow, though the effect of muscle weakness on body features may become more evident with time. Adults with NM typically have a very slender physique.

Mobility and orthopedics

Most children with mild NM eventually walk independently, although often at a later age than their peers. Some use wheelchairs or other devices to enhance their mobility. Individuals with severe NM generally have limited limb movement and use wheelchairs fulltime.

Because of weakness in the trunk muscles, people with NM are prone to scoliosis, which usually develops in childhood and worsens during puberty. Many individuals with NM undergo spinal fusion surgery to straighten and stabilize their backs. Osteoporosis is also common in NM.

Respiratory involvement

Attention to respiratory issues is critical to the health of all people with NM. Infants with severe NM frequently experience respiratory distress at or soon after birth. Many are ventilated via tracheostomy, and with proper breathing assistance they may attain good health. Though respiratory compromise may not be immediately apparent in people with intermediate or mild NM, it nearly always exists to some extent. As in many neuromuscular disorders, hypoventilation can begin insidiously, and it may cause serious health problems if not remedied by the use of noninvasive mechanical devices to assist breathing, particularly at night.

Communication and eating

Bulbar (throat) muscle weakness is a main feature of nemaline myopathy. Most individuals with severe NM are unable to swallow and receive their nutrition through feeding tubes. Most people with intermediate and mild NM take some or all of their nutrition orally. Bulbar muscle impairment may also lead to difficulty with communication. People with NM often have hypernasal speech as a result of poor closure of the velopharyngeal port (between the soft palate and the back of the throat). Communicative skills may be enhanced through speech therapy, oral prosthetic devices, surgery, and augmentative communication devices. Individuals with NM are usually highly sociable and intelligent, with a great desire to communicate.

Nemaline community

In 1999, the first non-medical webpage on nemaline myopathy was launched, and in October 2004, the first Nemaline Myopathy Convention was held in Toronto, Canada. A second convention took place in the summer of 2007 in Edinburgh, Scotland. In March 2006, Niki Shisler released a book, Fragile, in which she recounted her experiences surrounding the birth of twin sons with severe NM.

References

1. ^ "nemaline myopathy" at Dorland's Medical Dictionary
2. ^ "Clinical course correlates poorly with muscle pathology in nemaline myopathy -- Ryan et al. 60 (4): 665 -- Neurology". http://www.neurology.org/cgi/content/abstract/60/4/665. Retrieved 2009-02-18. 
3. ^ Schnell C, Kan A, North KN (June 2000). "'An artefact gone awry': identification of the first case of nemaline myopathy by Dr R.D.K. Reye". Neuromuscul. Disord. 10 (4-5): 307–12. doi:10.1016/S0960-8966(99)00123-6. PMID 10838259. http://linkinghub.elsevier.com/retrieve/pii/S0960896699001236. 

External links

• Nemaline Myopathy Support Group
• Nemaline Myopathy Foundation
• Muscular Dystrophy Association's (MDA) Information Page on Nemaline Myopathy
• A Washington University site delineating the various forms of NM
• GeneReview/NCBI/NIH/UW entry on Nemaline Myopathy
• http://www.buildingstrength.org A Foundation Building Strength Site contains numerous scientific references on the different types of NM, as well as information regarding diagnosis and management and the potential role of tyrosine in patients with Nemaline Myopathy
• Nemaline myopathy Genetic variations described/checked in SNPedia