This is a medical question of type : symptoms 
 What are the symptoms of Pelizaeus-Merzbacher disease ? 
 What are the signs and symptoms of Pelizaeus-Merzbacher disease? Pelizaeus-Merzbacher disease is divided into classic and severe (connatal) types. Although these two types differ in severity, their symptoms can overlap. Classic Pelizaeus-Merzbacher disease is the more common type. Within the first year of life, those affected with classic Pelizaeus-Merzbacher disease typically experience weak muscle tone (hypotonia), involuntary movements of the eyes (nystagmus), and delayed development of motor skills such as crawling or walking. As the child gets older, nystagmus may improve, but other movement disorders develop, including muscle stiffness (spasticity), problems with movement and balance (ataxia), and involuntary jerking (choreiform movements). Cognitive abilities may be impaired, but speech and language are usually present. Severe or connatal Pelizaeus-Merzbacher disease is the more severe of the two types. Symptoms are usually present at birth or develop in the first few weeks of life. Features include nystagmus, problems feeding, a whistling sound when breathing, progressive spasticity leading to joint deformities (contractures) that restrict movement, speech difficulties (dysarthria), ataxia, and seizures. Children often have short stature and poor weight gain. Those affected with connatal Pelizaeus-Merzbacher disease don't walk or develop effective use of their upper limbs. Verbal expression is usually severely affected, but comprehension may be significant. The Human Phenotype Ontology provides the following list of signs and symptoms for Pelizaeus-Merzbacher disease. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Nystagmus 100% Psychomotor deterioration 100% Abnormal pyramidal signs 90% Ataxia 90% Behavioral abnormality 90% Cerebral cortical atrophy 90% Decreased body weight 90% Developmental regression 90% Dystonia 90% Gait disturbance 90% Hypertonia 90% Incoordination 90% Kyphosis 90% Limitation of joint mobility 90% Muscular hypotonia 90% Optic atrophy 90% Premature birth 90% Progressive spastic quadriplegia 90% Scoliosis 90% Slow progression 90% Visual impairment 90% Choreoathetosis 75% Dysarthria 75% Dysphagia 75% Reduction of oligodendroglia 75% Sudanophilic leukodystrophy 75% Abnormality of the urinary system 50% Abnormality of visual evoked potentials 50% Arteriovenous malformation 50% Bowel incontinence 50% Chorea 50% Cognitive impairment 50% Delayed speech and language development 50% Failure to thrive 50% Head titubation 50% Hearing impairment 50% Microcephaly 50% Neurological speech impairment 50% Recurrent respiratory infections 50% Respiratory insufficiency 50% Seizures 50% Short stature 50% Congenital laryngeal stridor 7.5% Peripheral neuropathy 7.5% Hyporeflexia 4/7 Cerebral dysmyelination - Infantile onset - Intellectual disability - Rotary nystagmus - Scanning speech - Tremor - X-linked recessive inheritance - The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.