- Abnormality of the dentition (HP:0000164, a Human Phenotype Ontology term): Any abnormality of the teeth. Evidence: IEA. (OMIM:312750)
- Short foot (HP:0001773, a Human Phenotype Ontology term): A measured foot length that is more than 2 SD below the mean for a newborn of 27 - 41 weeks gestation, or foot that is less than the 3rd centile for individuals from birth to 16 years of age (objective). Alternatively, a foot that appears disproportionately short (subjective). Evidence: IEA. (OMIM:312750)
- Short stature (HP:0004322, a Human Phenotype Ontology term): A height below that which is expected according to age and gender norms. Although there is no universally accepted definition of short stature, many refer to "short stature" as height more than 2 standard deviations below the mean for age and gender (or below the 3rd percentile for age and gender dependent norms). Evidence: IEA. (OMIM:312750)
- Dystonia (HP:0001332, a Human Phenotype Ontology term): An abnormally increased muscular tone that causes fixed abnormal postures. There is a slow, intermittent twisting motion that leads to exaggerated turning and posture of the extremities and trunk. Evidence: IEA. (OMIM:312750)
- Seizure (HP:0001250, a Human Phenotype Ontology term): A seizure is an intermittent abnormality of nervous system physiology characterized by a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain. Evidence: PCS. Frequency: 1/1. (PMID:34778139)
- Cerebral cortical atrophy (HP:0002120, a Human Phenotype Ontology term): Atrophy of the cortex of the cerebrum. Evidence: IEA. (OMIM:312750)
- Abnormal T-wave (HP:0005135, a Human Phenotype Ontology term): An abnormality of the T wave on the electrocardiogram, which mainly represents the repolarization of the ventricles. Evidence: TAS. (OMIM:312750)
- Profound intellectual disability (HP:0002187, a Human Phenotype Ontology term): Profound intellectual disability (ID) is defined as a type of ID characterized by profoundly sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) below 20. Evidence: PCS. Frequency: 2/2. (PMID:9792883)
- Gait ataxia (HP:0002066, a Human Phenotype Ontology term): A type of ataxia characterized by the impairment of the ability to coordinate the movements required for normal walking. Gait ataxia is characteirzed by a wide-based staggering gait with a tendency to fall. Evidence: IEA. (OMIM:312750)
- Gastroesophageal reflux (HP:0002020, a Human Phenotype Ontology term): A condition in which the stomach contents leak backwards from the stomach into the esophagus through the lower esophageal sphincter. Evidence: IEA. (OMIM:312750)
- Gait apraxia (HP:0010521, a Human Phenotype Ontology term): Gait apraxia affecting the ability to make walking movements with the legs. Evidence: IEA. (OMIM:312750)
- Childhood onset (HP:0011463, a Human Phenotype Ontology term): Onset of disease at the age of between 1 and 5 years. Evidence: PCS. Frequency: 1/1. (PMID:34778139)
- Stereotypical hand wringing (HP:0012171, a Human Phenotype Ontology term): Habitual clasping and wringing of the hands in the middle of the body, similar to a hand-washing movement. Evidence: PCS. Frequency: 3/3. (PMID:9792883;PMID:34778139)
- X-linked dominant inheritance (HP:0001423, a Human Phenotype Ontology term): A mode of inheritance that is observed for dominant traits related to a gene encoded on the X chromosome. In the context of medical genetics, X-linked dominant disorders tend to manifest very severely in affected males. The severity of manifestation in females may depend on the degree of skewed X inactivation. Evidence: PCS. (PMID:9792883)
- Intermittent hyperventilation (HP:0004879, a Human Phenotype Ontology term): Episodic hyperventilation. Evidence: PCS. Frequency: 2/2. (PMID:9792883)
- Constipation (HP:0002019, a Human Phenotype Ontology term): Infrequent or difficult evacuation of feces. Evidence: IEA. (OMIM:312750)
- Skeletal muscle atrophy (HP:0003202, a Human Phenotype Ontology term): The presence of skeletal muscular atrophy (which is also known as amyotrophy). Evidence: IEA. (OMIM:312750)
- Motor deterioration (HP:0002333, a Human Phenotype Ontology term): Loss of previously present motor (i.e., movement) abilities. Evidence: PCS. Frequency: 2/2. (PMID:9792883)
- Bruxism (HP:0003763, a Human Phenotype Ontology term): Bruxism is characterized by the grinding of the teeth including the clenching of the jaw and typically occur during sleep. Evidence: IEA. (OMIM:312750)
- Truncal ataxia (HP:0002078, a Human Phenotype Ontology term): Truncal ataxia is a sign of ataxia characterized by instability of the trunk. It usually occurs during sitting. Evidence: IEA. (OMIM:312750)
- Scoliosis (HP:0002650, a Human Phenotype Ontology term): The presence of an abnormal lateral curvature of the spine. Evidence: IEA. (OMIM:312750)
- EEG abnormality (HP:0002353, a Human Phenotype Ontology term): Abnormality observed by electroencephalogram (EEG), which is used to record of the brain's spontaneous electrical activity from multiple electrodes placed on the scalp. Evidence: TAS. (OMIM:312750)
- Developmental regression (HP:0002376, a Human Phenotype Ontology term): Loss of developmental skills, as manifested by loss of developmental milestones. Evidence: PCS. Frequency: 3/3. (PMID:9792883;PMID:34778139)
- Secondary microcephaly (HP:0005484, a Human Phenotype Ontology term): Head circumference which falls below 2 standard deviations below the mean for age and gender because of insufficient head growth after birth. Evidence: IEA. (OMIM:312750)
- Prolonged QTc interval (HP:0005184, a Human Phenotype Ontology term): A longer than normal interval (corrected for heart rate) between the Q and T waves in the heart's cycle. Prolonged QTc can cause premature action potentials during late phase depolarizations thereby leading to ventricular arrhythmias and ventricular fibrillations. Evidence: TAS. (OMIM:312750)
- Kyphosis (HP:0002808, a Human Phenotype Ontology term): Exaggerated anterior convexity of the thoracic vertebral column. Evidence: IEA. (OMIM:312750)
- Autistic behavior (HP:0000729, a Human Phenotype Ontology term): Persistent deficits in social interaction and communication and interaction as well as a markedly restricted repertoire of activity and interest as well as repetitive patterns of behavior. Evidence: TAS. (OMIM:312750)
- Spasticity (HP:0001257, a Human Phenotype Ontology term): A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes. Evidence: IEA. (OMIM:312750)
- Apnea (HP:0002104, a Human Phenotype Ontology term): Lack of breathing with no movement of the respiratory muscles and no exchange of air in the lungs. This term refers to a disposition to have recurrent episodes of apnea rather than to a single event. Evidence: IEA. (OMIM:312750)
- Cachexia (HP:0004326, a Human Phenotype Ontology term): Severe weight loss, wasting of muscle, loss of appetite, and general debility related to a chronic disease. Evidence: IEA. (OMIM:312750)
These phenotypes are associated with the disease Rett syndrome (OMIM:312750, an entry in Online Mendelian Inheritance in Man).