- 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: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:2169)
- Megaloblastic bone marrow (HP:0001980): Abnormal increased number of megaloblasts in the bone marrow. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:2169)
- Hyperhomocystinemia (HP:0002160): An increased concentration of homocystine in the blood. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:2169)
- Microcephaly (HP:0000252): Head circumference below 2 standard deviations below the mean for age and gender. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Abnormality of the eye (HP:0000478): Any abnormality of the eye, including location, spacing, and intraocular abnormalities. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- 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: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- 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: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- 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: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Failure to thrive (HP:0001508): Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Intrauterine growth retardation (HP:0001511): An abnormal restriction of fetal growth with fetal weight below the tenth percentile for gestational age. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Macrocytic anemia (HP:0001972): A type of anemia characterized by increased size of erythrocytes with increased mean corpuscular volume (MCV) and increased mean corpuscular hemoglobin (MCH). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Vomiting (HP:0002013): Forceful ejection of the contents of the stomach through the mouth by means of a series of involuntary spasmic contractions. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Abnormal speech pattern (HP:0002167): An abnormality in the sound (volume) or cadence (rate) of speech. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Drowsiness (HP:0002329): Abnormal feeling of sleepiness or difficulty staying awake. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Abnormal cerebral white matter morphology (HP:0002500): An abnormality of the cerebral white matter. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Hypomethioninemia (HP:0003658): A decreased concentration of methionine in the blood. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Increased mean corpuscular volume (HP:0005518): Larger than normal size of erythrocytes. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Loss of consciousness (HP:0007185): Loss of awareness of oneself or one's surroundings, involving (i) a loss of normal motor control is evident as flaccidity or stiffness, either of which can be accompanied by jerking movements, and postural control is lost so that patients fall if they are in an upright position; (ii) normal responsiveness is lost; and (iii) the patient experiences amnesia for the event. Loss of consciousness my be transitory (e.g., syncope) or prolonged. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Postnatal growth retardation (HP:0008897): Slow or limited growth after birth. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Severe global developmental delay (HP:0011344): A severe delay in the achievement of motor or mental milestones in the domains of development of a child. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Feeding difficulties (HP:0011968): Impaired ability to eat related to problems gathering food and getting ready to suck, chew, or swallow it. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Brain atrophy (HP:0012444): Partial or complete wasting (loss) of brain tissue that was once present. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Abnormality of movement (HP:0100022): An abnormality of movement with a neurological basis characterized by changes in coordination and speed of voluntary movements. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2169)
- Hydrocephalus (HP:0000238): Hydrocephalus is an active distension of the ventricular system of the brain resulting from inadequate passage of CSF from its point of production within the cerebral ventricles to its point of absorption into the systemic circulation. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Hearing impairment (HP:0000365): A decreased magnitude of the sensory perception of sound. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Visual impairment (HP:0000505): Visual impairment (or vision impairment) is vision loss (of a person) to such a degree as to qualify as an additional support need through a significant limitation of visual capability resulting from either disease, trauma, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive correction, medication, or surgery. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Nystagmus (HP:0000639): Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Atypical behavior (HP:0000708): Atypical behavior is an abnormality in a person's actions that can be controlled or modulated by the will of the individual. While abnormal behaviors can be difficult to control, they are distinct from other abnormal actions that cannot be affected by the individual's will. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Hypertension (HP:0000822): The presence of chronic increased pressure in the systemic arterial system. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Abnormality of the skeletal system (HP:0000924): An abnormality of the skeletal system. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Osteoporosis (HP:0000939): Osteoporosis is a systemic skeletal disease characterized by low bone density and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility. According to the WHO criteria, osteoporosis is defined as a BMD that lies 2.5 standard deviations or more below the average value for young healthy adults (a T-score below -2.5 SD). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Syndactyly (HP:0001159): Webbing or fusion of the fingers or toes, involving soft parts only or including bone structure. Bony fusions are referred to as "bony" syndactyly if the fusion occurs in a radio-ulnar axis. Fusions of bones of the fingers or toes in a proximo-distal axis are referred to as "symphalangism". Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- 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: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Excessive daytime somnolence (HP:0001262): A state of abnormally strong desire for sleep during the daytime. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Abnormality of the liver (HP:0001392): An abnormality of the liver. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Abnormality of the cardiovascular system (HP:0001626): Any abnormality of the cardiovascular system. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Decreased total neutrophil count (HP:0001875): Abnormal decrease of absolute number of neutrophils in the blood, per microlitre, compared to a reference range for a given sex and age-group. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Pancytopenia (HP:0001876): An abnormal reduction in numbers of all blood cell types (red blood cells, white blood cells, and platelets). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Thromboembolism (HP:0001907): The formation of a blood clot inside a blood vessel that subsequently travels through the blood stream from the site where it formed to another location in the body, generally leading to vascular occlusion at the distant site. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Ventriculomegaly (HP:0002119): An increase in size of the ventricular system of the brain. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Hypoplasia of the brainstem (HP:0002365): Underdevelopment of the brainstem. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Deep venous thrombosis (HP:0002625): Formation of a blot clot in a deep vein. The clot often blocks blood flow, causing swelling and pain. The deep veins of the leg are most often affected. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Scoliosis (HP:0002650): The presence of an abnormal lateral curvature of the spine. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Hemolytic-uremic syndrome (HP:0005575): A thrombotic microangiopathy with presence of non-immune, intravascular hemolytic anemia, thrombocytopenia and acute kidney injury. A vicious cycle of complement activation, endothelial cell damage, platelet activation, and thrombosis is the hallmark of the disease. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Lower limb hypertonia (HP:0006895). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Peripheral neuropathy (HP:0009830): Peripheral neuropathy is a general term for any disorder of the peripheral nervous system. The main clinical features used to classify peripheral neuropathy are distribution, type (mainly demyelinating versus mainly axonal), duration, and course. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Delayed myelination (HP:0012448): Delayed myelination. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Widened subarachnoid space (HP:0012704): An increase in size of the anatomic space between the arachnoid membrane and pia mater. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Clinodactyly (HP:0030084): An angulation of a digit at an interphalangeal joint in the plane of the palm (finger) or sole (toe). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
- Glomerulopathy (HP:0100820): Inflammatory or noninflammatory diseases affecting the glomeruli of the nephron. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2169)
These phenotypes are associated with the disease Methylcobalamin deficiency type cblE (ORPHA:2169).