The following is taken with kind permission from the Chromosome 18 Registry and Research Society

Neurologic and Respiratory Changes

People with PTHS often have some changes in their muscle tone. Most often, they have decreased muscle tone. This is called hypotonia. Changes in muscle tone can lead to other difficulties. For example, infants with low muscle tone may have difficulty eating because the muscles surrounding the mouth are weak. Low muscle tone may also contribute to developmental delays. Physical, occupational, and speech therapy may improve hypotonia. Seizures are fairly common in people with PTHS. If seizures are suspected, a doctor may request an electroencephalogram (EEG). They may also refer the patient to a neurologist to help manage the seizures. Some individuals with PTHS have ataxia. People with ataxia usually have a hard time coordinating the movement of their arms and legs. It may make walking more difficult.

One of the most unique characteristics of PTHS is an abnormal breathing pattern. That is, many individuals with PTHS have episodes where they breathe more quickly or more shallowly than normal. This may lead to light-headedness; fainting; numbness and tingling in the hands and feet; and abdominal discomfort. Recently, a poster was presented that reported the successful treatment of hyperventilation in a child with Pitt-Hopkins syndrome. You can read about this report here.

MRI findings

Many people with PTHS have changes in the brain that can only be detected with an MRI. The most common change is a small corpus callosum. The corpus callosum is a bundle of nerves that connects the left and the right side of the brain. This can be associated with some of the neurological problems described above. Changes in the caudate nucleus have also been reported. The caudate nucleus is a part of the brain involved with learning and memory. The effects of these changes are not well-understood.

Eyes and vision

Vision problems are common in people with PTHS. The eyes may be crossed (strabismus). Near-sightedness (myopia) has also been reported. As vision problems are possible, people with PTHS should have regular eye exams.


People with PTHS may have a curvature of the spine (scoliosis). Foot abnormalities are also fairly common. The most common foot problem is flat feet (pes planus). However, other foot changes have been noted. For example, many people with PTHS have small and slender feet. People with foot or spinal problems may see an orthopaedic specialist. Braces and inserts, surgery, and therapy may help in addressing orthopaedic concerns.


Males with PTHS may have some changes in the genital region. The testicles may not be fully descended (cryptorchidism). In some cases, this may require surgical correction.


The most common gastrointestinal problem in people with PTHS is chronic constipation. This can happen during infancy, childhood, or adults. Medication may help this problem. Another common problem is reflux. Reflux occurs when the stomach contents flow upwards. This can cause pain, irritability, and vomiting. Medication may be helpful for people with reflux. In more severe cases, surgery may be required. A few conditions have been reported rarely in people with PTHS. Hirschsprung disease has been reported in one individual. This condition involves a change in the nerves of the large intestines. Pyloric stenosis has also been reported in one person. Pyloric stenosis is a closure or narrowing of the place where the stomach contents enter the intestines. If there is a concern for gastrointestinal problems, a referral to a gastroenterologist is appropriate.


In general, people with PTHS are shorter than other children and adults of the same age. In addition to short stature, many people with PTHS have microcephaly, or a head size that falls below the 3rd percentile.