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What is HADDS?

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Hypotonia Ataxia, and  Delayed  Development  Syndrome (HADDS) is a rare neurodevelopmental syndrome caused by a mutation (deletion, missense, frameshift, duplication, etc.) in the EBF3 gene on chromosome 10q26.3. EBF3-related HADDS generally affects the nervous system, muscle tone, speech, and general development. The syndrome was discovered in 2016 by Dr. Hsiao-Tuan Chao, Dr. Michael Francis Wangler and Dr. Hugo Bellen of Baylor College of Medicine in Houston, TX. 

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(L-R): Dr. Hsiao-Tuan Chao, Dr. Michael Francis Wangler and Dr. Hugo Bellen.

Common Symptoms


Loose, floppy muscles

Autism/ Autism-like Tendencies

  • Autism/ Autism-like tendencies may include lack of eye contact, Sensory Processing Disorder, repetitive activities, and stimming movements (ie: rocking, spinning, and hand flapping).


  • Balance issues, lack of muscle control or coordination of voluntary movements, such as walking or picking up objects.


Delayed Development

  • When a person does not reach their developmental milestones at the expected times. The delay can be major or minor and can occur in one or many areas—for example, gross motor, fine motor, language, social.


Eye and Vision Issues

  • Vision issues may include strabismus, lazy eye, poor vision, and delayed visual maturation.

Failure to Thrive/Body Abnormalities

  • Failure to thrive is defined as decelerated or arrested physical growth (height and weight measurements) and is associated with abnormal growth and development. Common body abnormalities/ dysmorphic features have been primarily documented in appendages/genital and face.


High Pain Tolerance  

  • Higher than normal pain tolerance or decreased reaction to pain.  High pain tolerance is noted when infants/ children do not cry during injections or when injured.


  • Loose, floppy muscles. Healthy muscles never fully relax; healthy muscles retain a rigidity and resistance to maintain posture. Hypotonic muscles are more relaxed and usually weaker than normal. Hypotonia can affect both voluntary and involuntary muscles. In some cases, over time, the hypotonia may correct and over-correct, becoming hypertonia and contractures. 


Speech Issues

  • Speech delays are common, often taking the form of apraxia, expressive language delays, and lack of verbal speech. 


Urology Issues

  • Urology Issues may include frequent UTIs, urine retention, incontinence, Neurogenic Bladder, vesicoureteral reflux, dysplastic kidney, duplicated ureter, undescended testicles, and other genital abnormalities.



Additional symptoms are: seizures, insomnia/restless sleep, Trichophagia/Pica, Neuro Itch, feeding/ swallowing issues, Pectus excavatum, difficultly expressing emotion, inability to smile, constipation, Neurogenic Bowel Dysfunction, foot abnormalities, mild facial dysmorphism, and pregnancy/ birth issues. 


Recently Diagnosed? Participate in the Research!

Join the active research study being conducted by Texas Children's Hospital (TCH), Baylor College of Medicine and the Jan and Dan Duncan Neurological Research Institute (NRI)
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Click the image to open the PDF.

Questions regarding the study? 

Email Dr. Chao's team at

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