- Hyperkinetic movements (HP:0002487): Motor hyperactivity with excessive movement of muscles of the body as a whole. Evidence: PCS. Frequency: 1/2. (PMID:12555939)
- Hypertonia (HP:0001276): A condition in which there is increased muscle tone so that arms or legs, for example, are stiff and difficult to move. Evidence: PCS. Frequency: 1/2. (PMID:12555939)
- Lethargy (HP:0001254): A state of fatigue, either physical or mental slowness and sluggishness, with difficulties in initiating or performing simple tasks. Distinguished from apathy which implies indifference and a lack of desire or interest in the task. A person with lethargy may have the desire, but not the energy to engage in personal or socially relevant tasks. Evidence: IEA. (OMIM:236270)
- Cerebral cortical atrophy (HP:0002120): Atrophy of the cortex of the cerebrum. Evidence: PCS. Frequency: 1/2. (PMID:12555939)
- Seizure (HP:0001250): 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: 1/2. (PMID:12555939)
- Hypotonia (HP:0001252): Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist. Evidence: PCS. Frequency: 1/2. (PMID:12555939)
- Infantile onset (HP:0003593): Onset of signs or symptoms of disease between 28 days to one year of life. Evidence: TAS. (OMIM:236270)
- Hyperhomocystinemia (HP:0002160): An increased concentration of homocystine in the blood. Evidence: PCS. Frequency: 2/2. (PMID:12555939)
- Failure to thrive (HP:0001508): Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm. Evidence: PCS. Frequency: 2/2. (PMID:12555939)
- Nystagmus (HP:0000639): Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms. Evidence: PCS. Frequency: 1/2. (PMID:12555939)
- Blindness (HP:0000618): Blindness is the condition of lacking visual perception defined as a profound reduction in visual perception. On the 6m visual acuity scale, blindness is defined as less than 3/60. On the 20ft visual acuity scale, blindness is defined as less than 20/400. On the decimal visual acuity scale, blindness is defined as less than 0.05. Blindness is typically characterized by a visual field of no greater than 10 degrees in radius around central fixation. Evidence: TAS. Frequency: Occasional (HP:0040283). (OMIM:236270)
- Megaloblastic anemia (HP:0001889): Anemia characterized by the presence of erythroblasts that are larger than normal (megaloblasts). Evidence: PCS. Frequency: 2/2. (PMID:12555939)
- Methylmalonic acidemia (HP:0002912): The concentration of methylmalonic acid in the blood circulation is above the upper limit of normal. Evidence: PCS. Frequency: 0/2. (PMID:12555939)
- Intellectual disability (HP:0001249): The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence. Evidence: IEA. (OMIM:236270)
- Decreased methionine synthase activity (HP:0003524): A reduction in methionine synthase activity. Evidence: IEA. (OMIM:236270)
- Neonatal onset (HP:0003623): Onset of signs or symptoms of disease within the first 28 days of life. Evidence: PCS. Frequency: 2/2. (PMID:12555939)
- Cerebral atrophy (HP:0002059): Atrophy (wasting, decrease in size of cells or tissue) affecting the cerebrum. Evidence: TAS. (OMIM:236270)
- Decreased circulating methylcobalamin concentration (HP:0003223): The concentration of methylcobalamin in the blood circulation is below the lower limit of normal. Methylcobalamin is a form of vitamin B12. Evidence: IEA. (OMIM:236270)
- Gait disturbance (HP:0001288): The term gait disturbance can refer to any disruption of the ability to walk. Evidence: TAS. (OMIM:236270)
- Homocystinuria (HP:0002156): An increased concentration of homocystine in the urine. Evidence: IEA. (OMIM:236270)
- Global developmental delay (HP:0001263): A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age. Evidence: PCS. Frequency: 2/2. (PMID:12555939)
- Methylmalonic aciduria (HP:0012120): Increased concentration of methylmalonic acid in the urine. Evidence: PCS. Frequency: 0/2. (PMID:12555939)
- Autosomal recessive inheritance (HP:0000007): A mode of inheritance that is observed for traits related to a gene encoded on one of the autosomes (i.e., the human chromosomes 1-22) in which a trait manifests in individuals with two pathogenic alleles, either homozygotes (two copies of the same mutant allele) or compound heterozygotes (whereby each copy of a gene has a distinct mutant allele). Evidence: PCS. (PMID:9501215)
- Hypomethioninemia (HP:0003658): A decreased concentration of methionine in the blood. Evidence: PCS. Frequency: 1/2. (PMID:12555939)
- Normocytic anemia (HP:0001897): A kind of anemia in which the volume of the red blood cells is normal. Evidence: PCS. Frequency: 2/2. (PMID:12555939)
These phenotypes are associated with the disease methylcobalamin deficiency type cblE (OMIM:236270).