Congenital muscular dystrophy

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Congenital muscular dystrophy
Autosomal recessive - en.svg
Autosomal recessive is generally the manner in which CMD is inherited
Specialty Neurology   OOjs UI icon edit-ltr-progressive.svg
Symptoms Muscle weakness [1]
Types17 types of CMD [1]
Diagnostic method NRI, EMG [2]
TreatmentCurrently there's no cure; one should monitor cardiac function and respiratory function [3]

Congenital muscular dystrophies are autosomal recessively-inherited muscle diseases. They are a group of heterogeneous disorders characterized by muscle weakness which is present at birth and the different changes on muscle biopsy that ranges from myopathic to overtly dystrophic due to the age at which the biopsy takes place. [1] [4]

Contents

Signs and symptoms

Muscle atrophy 1025 Atrophy.png
Muscle atrophy

Most infants with CMD will display some progressive muscle weakness or muscle wasting (atrophy), although there can be different degrees and symptoms of severeness of progression. The weakness is indicated as  hypotonia , or lack of muscle tone, which can make an infant seem unstable. [1] [5]

Children may be slow with their motor skills; such as rolling over, sitting up or walking, or may not even reach these milestones of life. Some of the rarer forms of CMD can result in significant learning disabilities.[ medical citation needed ]

Genetics

Congenital muscular dystrophies (CMDs) are autosomal recessively inherited, except in some cases of de novo gene mutation and Ullrich congenital muscular dystrophy. [6] [7] This means that in most cases, both parents must be carriers of a CMD gene in order for it to be inherited. CMDs are heterogenous and thus far there have been 35 genes discovered to be involved with different forms of CMD resulting from these mutations. [8] [6] There are different forms of CMD, often categorized by the protein changes caused by an atypical gene.

One group of forms is that for which a patient with affected genes displays defects in genes necessary to the function of the extracellular matrix. [7] One such form is merosin-deficient congenital muscular dystrophy (MDC1A), which accounts for around one-third of all CMD cases and is caused by mutations in the LAMA2 gene on the 6q2 chromosome, encoding for the laminin-α2 chain. [8] Laminin-α2 is an essential part of proteins like Laminin-2 and Laminin-4 that have important functions in muscle movement, and most patients with a mutated LAMA2 gene have no expression of Laminin-α2 in muscle tissue. [8] Another form in this group is Ullrich congenital muscular dystrophy, which is caused by mutations in the COL6A1, COL6A2 and COL6A3 genes that encode for three of the alpha chains making up Collagen VI. [9] Collagen VI is important in muscle, tendon, and skin tissue, and functions to attach cells to the extracellular matrix. [9] Ullrich CMD can be caused by both autosomal recessive or autosomal dominant mutations, although dominant mutations are usually de novo. [9] Recessive mutations often lead to a complete absence of Collagen VI in the extracellular matrix, while there are different types of dominant mutations that can cause partial function of Collagen V1. [9]

Another form of CMD is Rigid Spine Congenital Muscular Dystrophy (RSMD1), or Rigid Spine Syndrome, which is caused by mutations in the SEPN1 gene encoding for selenoprotein N. [8] The exact function of selenoprotein N is unknown, but it is expressed in the rough endoplasmic reticulum of skeletal muscle, heart, brain, lung, and placenta tissues, as well as at high levels in the diaphragm. [8] RSMD1 is characterized by axial and respiratory weakness, spinal rigidity and scoliosis, and muscular atrophy, and while it is a rare form of CMD, SEPN1 mutations are observed in other congenital myopathies. [7]

Some of the most common forms of CMDs are dystroglycanopathies caused by glycosylation defects of α-dystroglycan (α-DG), which helps link the extracellular matrix and the cytoskeleton. [10] Dystroglycanopathies are caused by mutations in genes encoding for proteins involved in modifying α-DG after translation of the protein, not mutations in the protein itself. [7] 19 genes have been discovered that cause α-DG-related dystrophies, with a wide range of phenotypic effects observed, characterized by brain malformations along with muscular dystrophy. [8] [10] Walker-Warburg syndrome (WWS) is the most severe dystroglycanopathy phenotype, with the POMT1 gene as the first reported causative gene, although there have been 11 additional genes implicated in WWS. These genes include POMT2, FKRP, FKTN, ISPD, CTDC2, TMEM5, POMGnT1, B3GALnT2, GMPPB, B3GnT1, and SGK196, many of which have been identified as involved in other dystroglycanopathies. [10] Patients display muscle weakness and cerebellar and ocular malformations, with a life expectancy of less than 1 year. [7] [10]

An additional dystroglycanopathy phenotype is Fukuyama congenital muscular dystrophy (FCMD) caused by a mutation in the Fukutin (FKTN) gene, which is the second most common type of muscular dystrophy in Japan after Duchenne muscular dystrophy. The founder mutation of FCMD is a 3- kilo base pair retrotransposon insertion in the noncoding region of FKTN, leading to muscle weakness, abnormal eye function, seizures, and intellectual disability. [9] While the exact function of FKTN is unknown, FKTN mRNA is expressed in fetuses in the developing CNS, muscles, and eyes, and is likely necessary for normal development since complete inactivation leads to embryonic death at 7 days. [8] Another phenotype, Muscle-eye-brain disease (MEB) is the dystroglycanopathy most prevalent in Finland, and is caused by mutations in the POMGnT1, FKRP, FKTN, ISPD, and TMEM5 genes. [10] The POMGnT1 gene is expressed in the same tissues as FKTN, and MEB appears to have a similar severity as FCMD. [8] However, symptoms unique to MEB include glaucoma, atrophy of the optic nerves, and retinal generation. [7] The least severe phenotype of dystroglycanopathies is CMD type 1c (MDC1C), caused by mutations in the FKRP and the LARGE gene, with a phenotype similar to MEB and WWS. [10] MDC1C also includes Limb-Girdle muscular dystrophy. [10]

Mechanism

In terms of the mechanism of congenital muscular dystrophy, one finds that though there are many types of CMD the glycosylation of α-dystroglycan and alterations in those genes that are involved are an important part of this conditions pathophysiology [11]

Diagnosis

Creatine kinase Creatine-Kinase.svg
Creatine kinase

For the diagnosis of congenital muscular dystrophy, the following tests/exams are done: [2]

Classification (different types of congenital muscular dystrophies)

The subtypes of congenital muscular dystrophy have been established through variations in multiple genes. Phenotype, as well as, genotype classifications are used to establish the subtypes, in some literature. [1]

One finds that congenital muscular dystrophies can be either autosomal dominant or autosomal recessive in terms of the inheritance pattern, though the latter is much more common [1]

Individuals with congenital muscular dystrophy fall into one of the following types:

  • CMD with brain-eye, also called muscle-eye-brain disease, [12] is a rare form of congenital muscular dystrophy (autosomal recessive disorder) causing a lack of normal muscle tone which can delay walking due to being weak, also paralysis of eye muscles and intellectual disability which affects an individuals way of processing information [12] It is caused by a mutation in the POMGNT1 gene. [12]
  • CMD with adducted (drawn inward) thumbs. a rare form of CMD causing permanent shortening of the toe joints and lack of muscle tone which can delay walking due to the individual being weak. The person with this form of congenital muscular dystrophy might have mild cerebellar hypoplasia in some cases . [1]
  • CMD/LGMD without MR-first years of a newborn begins with weakness, which affects motive skills, walking can be accomplished in adolescence, deformity and rigidity of joints. The joints, neck and spine; progressive cardiomyopathy at the early ages; cardiac rhythm abnormalities may be present in the individual. [1]
  • Large related CMD at the beginning of the newborn period, the issues the infant receives are; poor muscle tone and weak motor function; the individual will present with intellectual disability and the structure of the brain will likely be abnormal . [13]
  • CMD with cerebellar atrophy severe cerebellar hypoplasia, poor muscle tone, delayed in motor milestones, lack of coordination in motive skills, difficulty speaking, involuntary movements and some intellectual disability. Furthermore, muscle biopsy does not reveal any deficiency. [1]
  • Walker–Warburg syndrome at the beginning a progressive weakness and low muscle tone at birth or during early infancy; small muscles; the majority of affected children do not live more than 3 years of age. Eye structure problems are present, with accompanying visual impairment. [14]
  • CMD with primary laminin-α2 (merosin) deficiency (MDC1A) intellect in such individuals is unaffected, proximal muscle weakening and rigid spine are present along with respiratory involvement (with disease progression). [15]
  • CMD/LGMD with MR weakness and deformity and rigidity joints present at birth, poor muscle tone, slowly progressive; individuals may present with cerebellar cysts (or cortical problems), microcephaly may be present as well. Abnormal flexibility might occur, spinal curvature possible. [1]
  • CDG I (DPM3) some of the symptoms at birth and throughout the infant's life are weakness or poor muscle tone. The individual may present with cardiomyopathy (no outflow obstruction), a rise in serum creatine kinase might be present as well. Some IQ problems may be present, along with weakness in the proximal muscles. Also of note, a reduction of dolichol phosphate mannose . [16]
  • CDG I (DPM2) weak muscle tone starting in first weeks of the infant, the individual may show severe neurologic physical characteristics that result in fatality early in life. Hypotonia and myopathic facies may be present in such individuals, while contractures of joints may also be present. Finally, myoclonic seizures may occur at a very early age (3 months). [17]
  • CDG Ie (DPM1) at birth the infant will have weakness with involvement of the respiratory system, as well as, severe mental and psychomotor problems.By age of 3, the individual may be blind with speech problems. Microcephaly may occur in early childhood, as well as seizures. [18]
  • CMD with spinal rigidity present at birth can have poor muscle tone and weakness, reduced respiratory capacity, muscles could be deformed, beginning early ages stabilization or slow decline spinal rigidity, limited mobility to flex the neck and spine, spinal curvature and progressing deformity and rigidity joints, minor cardiac abnormalities, normal intelligence. [19]
Nasogastric tube Kendall stomach tube Fr18.jpg
Nasogastric tube
  • CMD with lamin A/C abnormality with in the first year the infant is weak, individual may have problems later lifting arms and head. May need nasogastric tube, limb weakness and elevated serum creatine kinase. Individual may show a diaphragmatic manner when breathing. [20]
  • Integrin α7 weakness which is present at birth, poor muscle tone with late walking, loss of muscle tissue, intellectual disability.Furthermore, the creatine kinase level was elevated. [21]
  • Fukuyama CMD -in Western countries this type of CMD is rare, but it is common in Japan. The effects this disease has on infants are on a spectrum of severity. They include weakness in muscle tone within the first year, deformed and rigid joints, spinal curvatures, seizures, eye involvement and intellectual disability. Some patients may achieve limited walking mobility. [22]
  • Merosin-deficient CMD- weakness in muscle tone present at birth, spectrum of severity; may show hypotonia and poor motor development. Most individuals have periventricular white matter problems. However, intellectual disability is rare in most cases. [23]
  • Merosin-positive CMD some forms of merosin-positive CMD are: Early spinal rigidity, CMD with muscle hypertrophy, CMD with muscle hypertrophy and respiratory failure. [24]
Scoliosis Wiki pre-op.jpg
Scoliosis
Will have some deformity and rigidity joints, some joints will have excessive flexibility, spinal rigidity, curvature, respiratory impairment, soft skin, normal cardiac function and normal intelligence. [25]

Differential diagnosis

The DDx of congenital muscular dystrophy, in an affected individual, is as follows (non-neuromuscular genetic conditions also exist [26] ): [2]

Management

Spinal fixation and fusion Roe LWS Spondylodese L5-S1 seitlich.jpg
Spinal fixation and fusion

In terms of the management of congenital muscular dystrophy the American Academy of Neurology recommends that the individuals need to have monitoring of cardiac function, respiratory, and gastrointestinal. Additionally it is believed that therapy in speech, orthopedic and physical areas, would improve the person's quality of life. [3]

While there is currently no cure available, it is important to preserve muscle activity and any available correction of skeletal abnormalities (as scoliosis). Orthopedic procedures, like spinal fusion, maintains/increases the individual's prospect for more physical movement. [3]

See also

Related Research Articles

Muscular dystrophy Genetic disorder

Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily affected, the degree of weakness, how fast they worsen, and when symptoms begin. Some types are also associated with problems in other organs.

Fukuyama congenital muscular dystrophy Medical condition

Fukuyama congenital muscular dystrophy (FCMD) is a rare, autosomal recessive form of muscular dystrophy mainly described in Japan but also identified in Turkish and Ashkenazi Jewish patients; fifteen cases were first described on 1960 by Dr. Yukio Fukuyama.

Hereditary inclusion body myopathies (HIBM) are a group of rare genetic disorders which have different symptoms. Generally, they are neuromuscular disorders characterized by muscle weakness developing in young adults. Hereditary inclusion body myopathies comprise both autosomal recessive and autosomal dominant muscle disorders that have a variable expression (phenotype) in individuals, but all share similar structural features in the muscles.

Walker–Warburg syndrome Medical condition

Walker–Warburg syndrome (WWS), also called Warburg syndrome, Chemke syndrome, HARD syndrome, Pagon syndrome, cerebroocular dysgenesis (COD) or cerebroocular dysplasia-muscular dystrophy syndrome (COD-MD), is a rare form of autosomal recessive congenital muscular dystrophy. It is associated with brain and eye abnormalities. This condition has a worldwide distribution. The overall incidence is unknown but a survey in North-eastern Italy has reported an incidence rate of 1.2 per 100,000 live births. It is the most severe form of congenital muscular dystrophy with most children dying before the age of three years.

<span class="mw-page-title-main">Centronuclear myopathy</span> Medical condition

Centronuclear myopathies (CNM) are a group of congenital myopathies where cell nuclei are abnormally located in the center of muscle cells instead of their normal location at the periphery.

Emery–Dreifuss muscular dystrophy Medical condition

Emery–Dreifuss muscular dystrophy (EDMD) is a type of muscular dystrophy, a group of heritable diseases that cause progressive impairment of muscles. EDMD affects muscles used for movement, causing atrophy, weakness and contractures. It almost always affects the heart, causing abnormal rhythms, heart failure, or sudden cardiac death. It is rare, affecting 0.39 per 100,000 people. It is named after Alan Eglin H. Emery and Fritz E. Dreifuss.

Congenital myopathy is a very broad term for any muscle disorder present at birth. This defect primarily affects skeletal muscle fibres and causes muscular weakness and/or hypotonia. Congenital myopathies account for one of the top neuromuscular disorders in the world today, comprising approximately 6 in 100,000 live births every year. As a whole, congenital myopathies can be broadly classified as follows:

Fukutin Mammalian protein found in Homo sapiens

Fukutin is a eukaryotic protein necessary for the maintenance of muscle integrity, cortical histogenesis, and normal ocular development. Mutations in the fukutin gene have been shown to result in Fukuyama congenital muscular dystrophy (FCMD) characterised by brain malformation - one of the most common autosomal-recessive disorders in Japan. In humans this protein is encoded by the FCMD gene, located on chromosome 9q31. Human fukutin exhibits a length of 461 amino acids and a predicted molecular mass of 53.7 kDa.

<span class="mw-page-title-main">Fukutin-related protein</span> Mammalian protein found in Homo sapiens

Fukutin-related protein (FKRP) is also known as FKRP_HUMAN, LGMD2I, MDC1C, MDDGA5, MDDGB5, and MDDGC5. FKRP can be located in the brain, cardiac muscle and skeletal muscle, and in cells it is found in the Golgi apparatus. Fukutin is expressed in the mammalian retina and is located in the Golgi complex of retinal neurons.

Micropolygyria is a neuronal migration disorder, a developmental anomaly of the brain characterized by development of numerous small convolutions (microgyri), causing intellectual disability and/or other neurological disorders. It is present in a number of specific neurological diseases, notably multiple sclerosis and Fukuyama congenital muscular dystrophy, a specific disease cause by mutation in the Fukutin gene (FKTN).

An Error has occurred retrieving Wikidata item for infobox Laminin subunit alpha-2 is a protein that in humans is encoded by the LAMA2 gene.

POMGNT1 Human gene

Protein O-linked-mannose beta-1,2-N-acetylglucosaminyltransferase 1 is an enzyme that in humans is encoded by the POMGNT1 gene.

POMT1 Mammalian protein found in Homo sapiens

Protein O-mannosyl-transferase 1 is an enzyme that in humans is encoded by the POMT1 gene. It is a member of the dolichyl-phosphate-mannose-protein mannosyltransferases.

Pikachurin Protein-coding gene in the species Homo sapiens

Pikachurin, also known as AGRINL (AGRINL) and EGF-like, fibronectin type-III and laminin G-like domain-containing protein (EGFLAM), is a protein that in humans is encoded by the EGFLAM gene.

X-linked spinal muscular atrophy type 2 Medical condition

X-linked spinal muscular atrophy type 2, also known as arthrogryposis multiplex congenita X-linked type 1 (AMCX1), is a rare neurological disorder involving death of motor neurons in the anterior horn of spinal cord resulting in generalised muscle wasting (atrophy). The disease is caused by a mutation in UBA1 gene and is passed in an X-linked recessive manner by carrier mothers to affected sons.

Ullrich congenital muscular dystrophy Medical condition

Ullrich congenital muscular dystrophy is a form of congenital muscular dystrophy. It is associated with variants of type VI collagen, it is commonly associated with muscle weakness and respiratory problems, though cardiac issues are not associated with this type of CMD. It is named after Otto Ullrich, who is also known for the Ullrich-Turner syndrome.

Collagen VI (ColVI) is a type of collagen primarily associated with the extracellular matrix of skeletal muscle. ColVI maintains regularity in muscle function and stabilizes the cell membrane. It is synthesized by a complex, multistep pathway that leads to the formation of a unique network of linked microfilaments located in the extracellular matrix (ECM). ColVI plays a vital role in numerous cell types, including chondrocytes, neurons, myocytes, fibroblasts, and cardiomyocytes. ColVI molecules are made up of three alpha chains: α1(VI), α2(VI), and α3(VI). It is encoded by 6 genes: COL6A1, COL6A2, COL6A3, COL6A4, COL6A5, and COL6A6. The chain lengths of α1(VI) and α2(VI) are about 1,000 amino acids. The chain length of α3(VI) is roughly a third larger than those of α1(VI) and α2(VI), and it consists of several spliced variants within the range of 2,500 to 3,100 amino acids.

LMNA-related congenital muscular dystrophy Medical condition

Lamin A/C congenital muscular dystrophy (CMD) is a disease that it is included in laminopathies. Laminopathies are caused, among other mutations, to mutations in LMNA, a gene that synthetizes lamins A and C.

<span class="mw-page-title-main">Muscle–eye–brain disease</span> Medical condition

Muscle–eye–brain (MEB) disease, also known as muscular dystrophy-dystroglycanopathy congenital with brain and eye anomalies A3 (MDDGA3), is a kind of rare congenital muscular dystrophy (CMD), largely characterized by hypotonia at birth. Patients have muscular dystrophy, central nervous system abnormalities and ocular abnormalities. The condition is degenerative.

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Further reading