Deafness-Dystonia-Optic Neuronopathy Syndrome: TIMM8A Gene Deletion/Duplication

Condition Description

Deafness-dystonia-optic neuronopathy (DDON) syndrome is an X-linked disorder in males characterized by certain manifestations at different ages.  Pre or postlingual sensorineural hearing impairment begins in early childhood; slowly progressive dystonia or ataxia manifests during the teens; slowly progressive decreased visual acuity from optic atrophy begins in the early 20s; and dementia begins around age 40.  Additionally, psychiatric symptoms, such as personality change and paranoia, may be progressive from childhood.  Age of onset and progression tends to be consistent for the hearing impairment; however the neurologic, visual, and neuropsychiatric signs vary in degree of severity and rate of progression.   Females may have mild hearing impairment and focal dystonia.

Mutations in TIMM8A (Xq22) cause DDON.  The TIMM8A gene encodes the mitochondrial import inner membrane translocase subunit Tim8 A protein and is involved in mitochondrial transport processes.  DDON syndrome can also be part of a contiguous gene deletion syndrome at Xq22 which includes the TIMM8A and BTK genes and included X-linked agammaglobulinemia.  The mutation detection rate is not yet known.

For patients with suspected DDON, sequence analysis is recommended as the first step in mutation identification. For patients in whom mutations are not identified by full gene sequencing, deletion/duplication analysis is appropriate.

References:
  • OMIM #300356:  Translocase of Inner Mitochondrial Membrane 8. 
  • Genetests

Genes (1)

Your search may have returned a result for a gene alias. Click here for a full list of genes and their aliases.

Indications

This test is indicated for:

  • Confirmation of a clinical diagnosis of deafness-dystonia-optic neuronopathy syndrome in an individual in whom sequence analysis was negative.
  • Carrier testing in adults with a family history of deafness-dystonia-optic neuronopathy syndrome in whom sequence analysis was negative.

Methodology

DNA isolated from peripheral blood is hybridized to a CGH array to detect deletions and duplications. The targeted CGH array has overlapping probes which cover the entire genomic region.

Detection

Detection is limited to duplications and deletions. The CGH array will not detect point or intronic mutations. Results of molecular analysis must be interpreted in the context of the patient's clinical and/or biochemical phenotype.

Specimen Requirements

When sample fails to meet the acceptable criteria, please call 470.378.2200 and ask to speak with a laboratory genetic counselor (eglgc@egl-eurofins.com).
Submit only 1 of the following specimen types
Whole Blood (EDTA)
WBP

Requirements
EDTA (Purple Top)
Infants and Young Children (<2 years of age): 2-3 ml
Children > 2 years of age to 10 years old: 3-5 ml
Older Children & Adults: 5-10 ml
Autopsy: 2-3 ml unclotted cord or cardiac blood
Collection and Shipping
Ship sample at room temperature for receipt at EGL within 24 hours of collection. Do not refrigerate or freeze.
DNA, Isolated
DNA

Requirements
Microtainer
3µg
Isolation using the Perkin Elmer™Chemagen™ Chemagen™ Automated Extraction method or Qiagen™ Puregene kit for DNA extraction is recommended.
Collection and Shipping
Refrigerate until time of shipment in 100 ng/µL in TE buffer. Ship sample at room temperature with overnight delivery.

Special Instructions

Submit copies of diagnostic biochemical test results with the sample, if appropriate. Contact the laboratory if further information is needed.

Sequence analysis is required before deletion/duplication analysis by targeted CGH array. If sequencing is performed outside of EGL Genetics, please submit a copy of the sequencing report with the test requisition.
  • Sequence analysis of the TIMM8A gene is available and is required before deletion/duplication analysis.  
  • Custom diagnostic mutation analysis (KM) is available to family members if mutations are identified by targeted mutation testing or sequencing analysis.
  • Prenatal testing is available only for known familial mutations to individuals who are confirmed carriers of mutations. Please contact the laboratory genetic counselor to discuss appropriate testing prior to collecting a prenatal specimen.

How to Order