motor neuropathy

Encephalopathy, Progressive, with Amyotrophy and Optic Atrophy

Clinical Characteristics
Ocular Features: 

Optic atrophy is present.

Systemic Features: 

This is a progressive neurodegenerative condition in which hypotonia and delayed development are evident between birth and 14 months of age.  Developmental milestones, if attained, soon regress accompanied by distal amyotrophy, cognitive impairment that may be severe, ataxia, spastic tetraplegia, dysarthria, and scoliosis.  Seizures often occur.

Brain imaging reveals cerebellar and cerebral atrophy.  Iron accumulation may be seen in the pallidum and substantia nigra.  The corpus callosum appears abnormally thin.  Muscle biopsy shows evidence of denervation atrophy.

Genetics

Homozygous or compound heterozygous mutations in the TBCE gene (1q42.3) can cause this disorder.  

Biallelic mutations in the same gene also cause Kenny-Caffey syndrome type 1 (244460) and a hypoparathyroidism dysmorphism syndrome (241410).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment has been reported.

References
Article Title: 

TBCE Mutations Cause Early-Onset Progressive Encephalopathy with Distal Spinal Muscular Atrophy

Sferra A, Baillat G, Rizza T, Barresi S, Flex E, Tasca G, D'Amico A, Bellacchio E, Ciolfi A, Caputo V, Cecchetti S, Torella A, Zanni G, Diodato D, Piermarini E, Niceta M, Coppola A, Tedeschi E, Martinelli D, Dionisi-Vici C, Nigro V, Dallapiccola B, Compagnucci C, Tartaglia M, Haase G, Bertini E. TBCE Mutations Cause Early-Onset Progressive Encephalopathy with Distal Spinal Muscular Atrophy. Am J Hum Genet. 2016 Oct 6;99(4):974-983.

PubMed ID: 
27666369

Biallelic Mutations in TBCD, Encoding the Tubulin Folding Cofactor D, Perturb Microtubule Dynamics and Cause Early-Onset Encephalopathy

Flex E, Niceta M, Cecchetti S, Thiffault I, Au MG, Capuano A, Piermarini E, Ivanova AA, Francis JW, Chillemi G, Chandramouli B, Carpentieri G, Haaxma CA, Ciolfi A, Pizzi S, Douglas GV, Levine K, Sferra A, Dentici ML, Pfundt RR, Le Pichon JB, Farrow E, Baas F, Piemonte F, Dallapiccola B, Graham JM Jr, Saunders CJ, Bertini E, Kahn RA, Koolen DA, Tartaglia M. Biallelic Mutations in TBCD, Encoding the Tubulin Folding Cofactor D, Perturb Microtubule Dynamics and Cause Early-Onset Encephalopathy. Am J Hum Genet. 2016 Oct 6;99(4):962-973.

PubMed ID: 
27666370

Spastic Paraplegia, Optic Atrophy, and Neuropathy

Clinical Characteristics
Ocular Features: 

Non-progressive optic atrophy with vision loss is described as congenital in onset.

Systemic Features: 

Progressive spasticity has its onset in infancy with loss of independent mobility usually in the second decade of life.  An exaggerated startle response occurs in some individuals.  All patients are confined to wheelchairs after 15 years of age due to progressive motor neuropathy.  No intellectual disability has been reported.  Joint contractures occur.  Dysarthria is notable in the third decade of life.  Eventually joint contractures and spine deformities occur.

Genetics

Homozygous mutations in the KLC2 gene (11q13.2) have been found in this disorder.  A homozygous 216-bp deletion in a non-coding region upstream of the gene results in overexpression of the gene not found in heterozygotes.  

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment has been described.

References
Article Title: 

Overexpression of KLC2 due to a homozygous deletion in the non-coding region causes SPOAN syndrome

Melo US, Macedo-Souza LI, Figueiredo T, Muotri AR, Gleeson JG, Coux G, Armas P, Calcaterra NB, Kitajima JP, Amorim S, Olavio TR, Griesi-Oliveira K, Coatti GC, Rocha CR, Martins-Pinheiro M, Menck CF, Zaki MS, Kok F, Zatz M, Santos S. Overexpression of KLC2 due to a homozygous deletion in the non-coding region causes SPOAN syndrome. Hum Mol Genet. 2015 Dec 15;24(24):6877-85.

PubMed ID: 
26385635

Charcot-Marie-Tooth Disease(s)

Clinical Characteristics
Ocular Features: 

Optic atrophy is present in some patients, particularly in X-linked recessive (CMTX5; 311070), X-linked dominant (CMTX5; 302800), and autosomal recessive (CMT2A2B; 617087) disease.  Congenital and juvenile-onset open-angle glaucoma has been reported among members of 2 consanguineous families with type 4B2, or CMT4B2; (604563).  The mean age of onset was 8 years.

Systemic Features: 

Charcot-Marie-Tooth disease is a large group of clinically and genetically heterogeneous disorders characterized by progressive motor and sensory polyneuropathy.  These can be separated (with overlap) into two large groups on the basis of electrophysiologic criteria: type 1 is the demyelinating form, and type 2 the axonal form.  Patients with primarily distal motor neuropathy are sometimes considered to comprise a third type.

 Symptoms such as weakness in the extremities and digits have a variable age of onset but usually become evident in late childhood or early adulthood.  Small muscles of the hands and feet are often atrophied to some degree.  Some patients develop hearing loss of the neurosensory type.  Foot deformities such as pes cavus are common.  Nerve conduction velocity (reduction) and electromyography can be helpful diagnostically.  It may be helpful to look for characteristic changes such as loss of myelinated fibers and focal myelin sheath folding in sural nerve biopsies.  Intellectual impairment and dementia are usually not features of Charcot-Marie-Tooth disease.

Hemizygous individuals with X-linked types of CMT such as CMTX2-5 seem to be more likely to have intellectual disabilities, hearing loss, spasticity, and optic neuropathy.

Genetics

Charcot-Marie-Tooth disease can also be classified on the basis of their hereditary patterns including autosomal dominant, autosomal recessive, X-linked recessive, and X-linked dominant.  Each of these contains yet more distinct subtypes as defined by mutations in at least 40 genes.

The wide range of disease severity and the overlapping of many signs can make pedigree construction and the determination of recurrence risks and prognosis challenging.  The only recourse may be genotyping.

See Charcot-Marie-Tooth Disease with Glaucoma (604563) for a form of this disease in which glaucoma occurs early.

Pedigree: 
Autosomal dominant
Autosomal recessive
X-linked dominant, father affected
X-linked dominant, mother affected
X-linked recessive, carrier mother
X-linked recessive, father affected
Treatment
Treatment Options: 

The widespread and debilitating polyneuropathy requires a multidisciplinary management approach with neurologists, physical and occupational therapists, audiologists, pain specialists, and orthopedists.  Pharmaceuticals such as gabapentin may be used for neuropathic pain.  Surgery for pes cavus and joint dysplasias can be helpful.

References
Article Title: 

Charcot-Marie-Tooth disease

Carter GT, Weiss MD, Han JJ, Chance PF, England JD. Charcot-Marie-Tooth disease. Curr Treat Options Neurol. 2008 Mar;10(2):94-102.

PubMed ID: 
18334132

Mutations in MTMR13, a new pseudophosphatase homologue of MTMR2 and Sbf1, in two families with an autosomal recessive demyelinating form of Charcot-Marie-Tooth disease associated with early-onset glaucoma

Azzedine H, Bolino A, Taieb T, Birouk N, Di Duca M, Bouhouche A, Benamou S, Mrabet A, Hammadouche T, Chkili T, Gouider R, Ravazzolo R, Brice A, Laporte J, LeGuern E. Mutations in MTMR13, a new pseudophosphatase homologue of MTMR2 and Sbf1, in two families with an autosomal recessive demyelinating form of Charcot-Marie-Tooth disease associated with early-onset glaucoma. Am J Hum Genet. 2003 May;72(5):1141-53.

PubMed ID: 
12687498

Ataxia with Oculomotor Apraxia 1

Clinical Characteristics
Ocular Features: 

Patients with this disorder have difficulty initiating voluntary ocular movements upon command or when following targets (oculomotor apraxia).  Gaze changes are often initiated first by head thrusting, followed by saccadic eye movements.  One may test for this by holding the head whereupon the patient is unable to move the eyes.  Ocular apraxia is often evident a few years after symptoms of ataxia are noted and may progress to external ophthalmoplegia.  Most patients have exaggerated blinking.

Systemic Features: 

The ataxia is cerebellar in origin with onset usually in the first decade of life (mean age of onset 4.3 years). It is associated with peripheral axonal neuropathy and hypoalbuminemia. Gait imbalance is usually the first symptom followed by upper limb dysmetria.  Other variable signs include dysarthria, choreiform or athetoid movements, facial grimacing, tongue and limb fasciculations, areflexia, and distal sensory deficits.   All symptoms are progressive and ambulation is lost within a decade of onset.  Cerebellar atrophy may be seen on MRI and the EMG shows evidence of axonal neuropathy.  Mental function is normal in most patients but some have cognitive impairments.

Genetics

Mutations in the APTX gene (9p21.1) encoding aprataxin are responsible for this autosomal recessive condition. 

There is evidence of clinical and genetic heterogeneity.  At least two loci are involved, with the mutation at 9p13 causing an earlier onset of disease (first decade), and hypoalbuminemia, while the second one, ataxia with oculomotor apraxia 2  [606002]) at 9q34 causes a disorder of later onset (2nd or third decade) in which oculomotor apraxia is an inconsistent finding.  Oculomotor apraxia is more consistently found in the disorder described here.  Cogan-type oculomotor apraxia (257550) lacks other neurologic signs.

See also Ataxia with Oculomotor Apraxia 3 (615217), and Ataxia with Oculomotor Apraxia 4 (616267).

Oculomotor apraxia may be the presenting sign in Gaucher disease (230800, 230900, 231000). 

The ocular phenotype is similar to that seen in ataxia-telangiectasia (208900).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No specific treatment is available although physical therapy can be helpful.

References
Article Title: 

Aprataxin gene mutations in Tunisian families

Amouri R, Moreira MC, Zouari M, El Euch G, Barhoumi C, Kefi M, Belal S, Koenig M, Hentati F. Aprataxin gene mutations in Tunisian families. Neurology. 2004 Sep 14;63(5):928-9.

PubMed ID: 
15365154
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