Supplemental Data: TUBB4A de novo mutations cause isolated hypomyelination

A. Pizzino, MGC1*, T. Pierson, MD, PhD2,3,4,*, Y. Guo, PhD5*, G. Helman, BS1, S. Fortini, MD6, K. Guerrero,M.sC7, S. Saitta MD, PhD2,8, JLP. Murphy, CPNP1, Q. Padiath, MBBS, PhD9, Y. Xie, B.Sc10,11, H. Hakonarson, MD, PhD5,12,13, X. Xu, PhD10,11, T. Funari, MS, CGC3,4,8, M. Fox, MS, LCGC14, RJ. Taft, PhD15, MS. van der Knaap, MD, PhD16, G. Bernard, MD, MSc, FRCPC7, R. Schiffmann, MD17, C. Simons, PhD15#, A. Vanderver, MD1,18 #

  1. Department of Neurology, Children's National Medical Center, Washington, DC, USA
  2. Department of Pediatrics, Cedars-Sinai Medical Center, Los Angeles, CA, USA
  3. Department of Neurology, Cedars-Sinai Medical Center, Los Angeles, CA, USA
  4. Regenerative Medicine Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
  5. Center for Applied Genomics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
  6. Department of Pediatric Neurology, Hospital Nacional de Pediatria Juan P. Garrahan. Buenos Aires, Argentina
  7. Departments of Pediatrics, Neurology and Neurosurgery, Division of Pediatric Neurology, Montreal Children's Hospital, McGill University Heath Center,Montreal, Quebec, Canada
  8. Medical Genetics Institute, Cedars-Sinai Medical Center,Los Angeles, CA, USA
  9. Department of Human Genetics Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
  10. BGI-Shenzhen, Shenzhen 518083, China
  11. Guangdong Enterprise Key Laboratory of Human Disease Genomics, BGI-Shenzhen, Shenzhen 518083, China
  12. Division of Human Genetics, The Children’s Hospital of Philadelphia, Philadelphia, PA, USA
  13. Department of Pediatrics, The Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
  14. Department of Pediatrics, University of California, Los Angeles, Los Angeles, CA, USA
  15. Institute for Molecular Bioscience, University of Queensland, St. Lucia, Queensland, Australia
  16. Department of Child Neurology, VU University Medical Center, Amsterdam, NL
  17. Institute of Metabolic Disease, Baylor Research Institute, Dallas, Texas, USA
  18. Center for Genetic Medicine Research, Children's National Medical Center, Washington, DC, USA

*These authors contributed equally to the manuscript

# Denotes Senior Author

Communicating author:
Adeline Vanderver
Children's National Medical Center
Center for Genetic Medicine Research (CGMR)
111 Michigan Avenue, NW
Washington, DC 20010-2970
+1-202-476-6230

Search Terms: Genetic Linkage [94],Leukodystrophies [155], Pediatric [227]

Word Count: 1,162

Abstract word count: 143

Title Character Count: 55

AV, GH, AP, CS, and MSK managed the project. TMP, SF, SS, JLPM, RS, and AV performed clinical examination, AP, TF, and MF provided genetic counseling. TMP, YG, KG, QP, YX, HN, XX, TF, RJT, GB, and CS performed sequencing. AV and CS designed the analyses. CS, GB, YH performed the data analyses. AP, TMP, GH, SF, JLPM, MSK, CS, and AV wrote the paper.

AV provides unpaid consulting to StemCells Inc. Her involvement was supported by a K08 from NINDS. GB has received compensation from Actelion Pharmaceuticals, Genzyme, Shire and Santhera Pharmaceuticals(speaker’s honoraria and for serving on scientific advisory boards). Otherwise, the authors report no conflicts of interest.

Supplemental Data-Clinical details of reported patients

Patient 1

Patients 1 and 2 are a sibling pair born to non-consanguinous parents with a negative family history for neurological diseases.Patient 1 was diagnosed with a learning disability in childhood and formal intelligence testing demonstrated mild intellectual disability. She had difficulty with classwork,but nonetheless graduated from high school. At age two, she fractured her right leg and upon removal of the cast, her foot was noted to be “turned in.” General clumsiness was noted throughout her life,and balance issues were noted in her teens. She developed mild hearing loss in the left ear in adulthood. She developed a slowly progressive spastic paraplegia, in addition to mild speech dysarthria, bowel incontinence, and lactose intolerance. Formal intelligence quotient (IQ) testing at age 42 revealed an IQ of 60. At time of last contact she had been working part-time at a bakery for at least 9 years. Physical exam at 46 yearsdemonstrated a spastic gait, slight weakness of the left armand dystonic posturing of left armduring ambulation. She had a mild intention tremor, hyperreflexia, bilateral clonus, andbilateral extensor plantar responses. Nerve conduction studies were normal.Somatosensory evoked potentials were not performed. Neuro-ophthalmological exam revealed bilateral optic atrophy.Auditory evoked potentials demonstrated delayed interpeak latency indicating slowed brainstem auditory conduction.

TUBB4A mutations were discovered via exome sequencing.

Patient 2

Patient 2 is the younger brother of patient 1. At age five he was diagnosed with learning disabilities and was in special education classes throughout his schooling. He was reported to have visual difficulties in addition to speech difficulties.Spastic paraparesis started in early childhood. As a child he was reported to stumble often and have difficulty walking. In adulthood he noted some slowly progressivehypophonia that resolved over the course of one year under speech therapy. He also had gastroesophageal reflux but did not report any bowel concerns. Formal intelligence quotient (IQ) testing at age 40 revealed an IQ of 54. He graduated from the 12th grade and at last contact with patient at age 42, had been able to hold a full-time position at a large national hardware chain store for over one year.On physical exam at 42 years of age he was noted to have slight facial asymmetry at rest, spastic gait, dystonic posturing of the arms when walking, hyperreflexia and bilateral Babinski’s. Auditory evoked potential testing demonstrated slowed brainstem response. Somatosensory evoked potentials and nerve conduction velocity testing were not performed. Neuro-ophthalmological exam revealed mild bilateral optic atrophy.

TUBB4A mutations were discovered via exome sequencing.

Patient 3

Patient 3 is born from non-consanguinous parents and the family history was negative for neurological diseases. His early gross motor development was slightly delayed, with unsupported waking achieved at the age of 19 months, with somewhat unstable gait and frequent falls from the beginning. Fine motor difficulties were noticed around the age of 3 years, when the parents had noticed a tremor when he was drawing. The rest of his developmental milestones were reached on time. The patient was first seen for gait and speech abnormalities at four years of age. On examination at the time, he had a subtle nystagmus, which retrospectively had been present since birth. He had mild spasticity of the legs and reflexes were increased, more so in the legs than the arms, with sustained ankle clonus and bilateral Babinski’s. He had significant gait ataxia, mild truncal ataxia while sitting, and dysmetria of arms and legs. Over the following several years, his gait deteriorated and he developed dystonic posturing of the legs by age 6. Nerve conduction studies were normal. Ophthalmological evaluation showed bilateral optic disc pallor. Auditory evoked responses revealed abnormal conduction at the level of the pons. Somatosensory evoked potentials and nerve conduction velocity testing were not performed.His cognition remained intact, with good grades at school and normal IQ when formally tested.

His TUBB4A mutations were discovered via exome sequencing.

Patient 4

Patient 4 was born to non-consanguinous parents with a negative family history for neurological diseases. Parents noted in infancy that she was a slow feeder and had difficulty with latching onto the breast. She developed “uncontrolled movements” around 1 month of age and over the next months was noted to have poor head control and delayed motor milestones. She rolled over at approximately 4 months and said her first words (mama and dada) at 2 years of age. Her parents noted that her receptive language was more developed than her expressive language and she could follow some simple commands. She never showed signs of regression. On examination at 5years, axial tone was decreased, while appendicular tone was increased with notable spastic paraparesis. She was hyperreflexic throughout with bilateral ankle clonus and extensor plantar responses. Her posture was ataxic. She had strabismus. Auditory evoked response testing was normal. Somatosensory evoked potentials and nerve conduction velocity testing were not performed.

Whole exome sequencing identified the TUBB4A mutation.

Patient 5

Patient 5 was born to non-consanguineous parents with a negative family history for neurological diseases. The patient came to attention at 9 months when parents noted that he had decreased tone and was unable to sit without support, pull to quadruped or crawl. He developed progressive appendicular weakness and had increased tone in the arms more than the legs. Progressive motor difficulties and stable dysarthria persisted throughout childhood. By 10 years the patient had increased difficulty with ambulation requiring a walker for distance. Autonomic dysregulation with flushing and discoloration of dependent limbs was noted. The patient did not have any physical or developmental regression and academic performance was at peer level until age 7, despite notable problems with concentration and a diagnosis of ADHD. At 12 years of age there were events concerning for seizures but EEG was normal. On physical exam he had a mild spastic diplegia with increased deep tendon reflexes and tone. He had choreiform movements of the upper extremities. Somatosensory evoked potentials and nerve conduction velocity testing were not performed.Whole exome sequencing identified his TUBB4A mutation.