- Delayed CNS myelination (HP:0002188): Delayed myelination in the central nervous system. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Dystonia (HP:0001332): 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: PCS. Frequency: 1/1. (PMID:18385497)
- 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:18385497)
- Cerebellar atrophy (HP:0001272): Cerebellar atrophy is defined as a cerebellum with initially normal structures, in a posterior fossa with normal size, which displays enlarged fissures (interfolial spaces) in comparison to the foliae secondary to loss of tissue. Cerebellar atrophy implies irreversible loss of tissue and result from an ongoing progressive disease until a final stage is reached or a single injury, e.g. an intoxication or infectious event. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- 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: 1/1. (PMID:18385497)
- Abnormal vitamin B12 concentration (HP:0004341): The concentration of vitamin B12 (or one of its metabolites) in the blood circulation is outside the limits of normal. Evidence: PCS. Frequency: 0/1. (PMID:18385497)
- Infantile onset (HP:0003593): Onset of signs or symptoms of disease between 28 days to one year of life. Evidence: PCS. Frequency: 1/2. (PMID:18385497)
- Hyperhomocystinemia (HP:0002160): An increased concentration of homocystine in the blood. Evidence: PCS. Frequency: 2/2. (PMID:18385497)
- Severe intellectual disability (HP:0010864): Severe intellectual disability (ID) is defined as a type of ID characterized by severely sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) the range of 20-34. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Nystagmus (HP:0000639): Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Increased circulating folate concentration (HP:0032164): The concentration of folic acid in the blood circulation is above the upper limit of normal. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Anemia (HP:0001903): A reduction in erythrocytes volume or hemoglobin concentration. Evidence: PCS. Frequency: 0/1. (PMID:18385497)
- Childhood onset (HP:0011463): Onset of disease at the age of between 1 and 5 years. Evidence: PCS. Frequency: 1/2. (PMID:18385497)
- Aggressive behavior (HP:0000718): Behavior or an act aimed at harming a person, animal, or physical property (e.g., acts of physical violence; shouting, swearing, and using harsh language; slashing someone's tires). Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Reduced eye contact (HP:0000817): A reduced frequency or duration of eye contact. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Megaloblastic anemia (HP:0001889): Anemia characterized by the presence of erythroblasts that are larger than normal (megaloblasts). Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Hyperactivity (HP:0000752): Hyperactivity is a condition characterized by constant and unusually high levels of activity, even in situations where it is deemed inappropriate. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Cerebellar vermis hypoplasia (HP:0001320): Underdevelopment of the vermis of cerebellum. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Cerebral atrophy (HP:0002059): Atrophy (wasting, decrease in size of cells or tissue) affecting the cerebrum. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Absent speech (HP:0001344): Complete lack of development of speech and language abilities. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Spastic ataxia (HP:0002497). Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- Gait disturbance (HP:0001288): The term gait disturbance can refer to any disruption of the ability to walk. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
- 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: 1/1. (PMID:18385497)
- Abnormal circulating folate concentration (HP:0040087): Any deviation from the normal concentration of folate in the blood circulation. Evidence: PCS. Frequency: 0/1. (PMID:18385497)
- Methylmalonic aciduria (HP:0012120): Increased concentration of methylmalonic acid in the urine. Evidence: PCS. Frequency: 0/1. (PMID:18385497)
- 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:18385497)
- Increased mean corpuscular volume (HP:0005518): Larger than normal size of erythrocytes. Evidence: PCS. Frequency: 2/2. (PMID:18385497)
- Hypomethioninemia (HP:0003658): A decreased concentration of methionine in the blood. Evidence: PCS. Frequency: 2/2. (PMID:18385497)
- Absent Achilles reflex (HP:0003438): Absence of the Achilles reflex (also known as the ankle jerk reflex), which can normally be elicited by tapping the tendon is tapped while the foot is dorsiflexed. Evidence: PCS. Frequency: 1/1. (PMID:18385497)
These phenotypes are associated with the disease homocystinuria-megaloblastic anemia cblD type (OMIM:620952).