delayed motor development

Myopathy, Mitochondrial Anomalies, and Ataxia

Clinical Characteristics
Ocular Features: 

Ocular findings are variable.  One of three individuals with compound heterozygous mutations had a pigmentary retinopathy with pallor of the optic nerve but no visual abnormalities.  Her sister had only optic nerve pallor.  The eyes are described as "small" and "close-set".

No ocular findings were reported for the family with autosomal dominant inheritance.

Systemic Features: 

Ataxia, short stature, and gait difficulties from an early age are consistent findings.  Some patients are never able to walk.  Motor development is generally delayed.  Truncal and limb ataxia is a feature.  Some degree of intellectual disability is generally present and speech is often delayed.  

The face is long with a myopathic appearance.  Both micrognathia and a prominent jaw may be seen.  The palate is highly arched.  Patients are described as hypotonic and there is generalized muscle weakness both proximal and distal.  Distal sensory impairment has been described in the family with presumed dominant inheritance and there may be psychiatric symptoms of anxiety, depression, and schizophrenia.  Dysmetria with dysdiadochokinesis is often present and a fine intention tremor has been observed.

Mitochondria in fibroblasts exhibit abnormal dynamics and occur in a fragmented network.  Muscle biopsies reveal changes consistent with myopathy.  Serum creatine kinase may be elevated.

Genetics

Compound heterozygous mutations in the MSTO1 gene (1q22) have been found in two families with 3 affected individuals suggesting autosomal recessive inheritance.  In a third family, heterozygous mutations in the same gene were found in a mother and 3 of her adult children, consistent with autosomal dominant transmission.

Pedigree: 
Autosomal dominant
Autosomal recessive
Treatment
Treatment Options: 

No treatment has been reported.

References
Article Title: 

Cataracts, Growth Hormone Deficiency, and Skeletal Dysplasia

Clinical Characteristics
Ocular Features: 

Lens opacities can be seen in infancy or childhood and may be congenital in onset.  Nystagmus has been noted in one patient. 

Systemic Features: 

There is considerable clinical heterogeneity in the phenotype.  Motor milestones may be slightly delayed.  Dysmorphic features in at least some individuals include bushy eyebrows, a prominent forehead, and a small mouth.  Thoracic scoliosis and genu valgum may be present.  Physical growth is reduced during infancy and childhood resulting in a short stature in adulthood.  Growth hormone and cortisol deficiency have been documented. Episodic hypoglycemia has been documented. The pituitary adenohypophysis appears atrophied on MRI.

Neurosensory hearing loss has been diagnosed in the first two years of life.  A distal sensory neuropathy with loss of pain, temperature and touch sensation may be present late in the first decade of life.  There are no cognitive deficits and patients can live independently.

Genetics

This is likely an autosomal recessive disorder resulting from homozygous or compound heterozygous mutations in the IARS2 gene (1q41).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Appropriate hormonal replacement therapy can be beneficial.  Individual skeletal surgery for scoliosis and hip dislocation should be considered.  Visually significant lens opacities may require surgery.

References
Article Title: 

Mutation in The Nuclear-Encoded Mitochondrial Isoleucyl-tRNA Synthetase IARS2 in Patients with Cataracts, Growth Hormone Deficiency with Short Stature, Partial Sensorineural Deafness, and Peripheral Neuropathy or with Leigh Syndrome

Schwartzentruber J, Buhas D, Majewski J, Sasarman F, Papillon-Cavanagh S, Thiffaut I, Sheldon KM, Massicotte C, Patry L, Simon M, Zare AS, McKernan KJ; FORGE Canada Consortium, Michaud J, Boles RG, Deal CL, Desilets V, Shoubridge EA, Samuels ME. Mutation in The Nuclear-Encoded Mitochondrial Isoleucyl-tRNA Synthetase IARS2 in Patients with Cataracts, Growth Hormone Deficiency with Short Stature, Partial Sensorineural Deafness, and Peripheral Neuropathy or with Leigh Syndrome. Hum Mutat. 2014 Nov;35(11):1285-9.

PubMed ID: 
25130867
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