- 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: 1/1. (PMID:8874222)
- Opisthotonus (HP:0002179): Opisthotonus is defined as a dramatic abnormal posture due to spastic contraction of the extensor muscles of the neck, trunk, and lower extremities that produces a severe backward arching from neck to heel. In most cases, the trunk is elevated off the ground by a few inches. It is usually sudden in onset and can be sustained or repetitive. It can be considered a variant of decerebrate posturing involving a hyperextension of the neck, back, and limbs. Evidence: TAS. (OMIM:250800)
- Microcephaly (HP:0000252): Head circumference below 2 standard deviations below the mean for age and gender. Evidence: IEA. (OMIM:250800)
- Strabismus (HP:0000486): A misalignment of the eyes so that the visual axes deviate from bifoveal fixation. The classification of strabismus may be based on a number of features including the relative position of the eyes, whether the deviation is latent or manifest, intermittent or constant, concomitant or otherwise and according to the age of onset and the relevance of any associated refractive error. Evidence: IEA. (OMIM:250800)
- Decreased erythrocyte nicotinamide adenine dinucleotide-cytochrome b5 reductase activity (HP:6000133): The activity of nicotinamide adenine dinucleotide (NADH)-cytochrome b5 reductase in erythrocytes (red blood cells) is below the lower limit of normal. Evidence: PCS. Frequency: 1/1. (PMID:8874222)
- 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:8874222)
- Methemoglobinemia (HP:0012119): Abnormally increased levels of methemoglobin in the blood. In this form of hemoglobin, there is an oxidized ferric iron (Fe +3) rather than the reduced ferrous form (Fe 2+) that is normally found in hemoglobin. Methemoglobin has a reduced affinity for oxygen, resulting in a reduced ability to release oxygen to tissues. Evidence: TAS. Frequency: 1/1. (OMIM:250800)
- 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:8874222)
- Esodeviation (HP:0020045): A manifest or latent ocular deviation in which one or both eyes tends to deviate nasally. Evidence: PCS. Frequency: 1/1. (PMID:8874222)
- Polycythemia (HP:0001901): Polycythemia is diagnosed if the red blood cell count, the hemoglobin level, and the red blood cell volume all exceed the upper limits of normal. Evidence: TAS. (OMIM:250800)
- Cyanosis (HP:0000961): Bluish discoloration of the skin and mucosa due to poor circulation or inadequate oxygenation of arterial or capillary blood. Evidence: PCS. Frequency: 1/1. (PMID:8874222)
- Headache (HP:0002315): Cephalgia, or pain sensed in various parts of the head, not confined to the area of distribution of any nerve. Evidence: IEA. (OMIM:250800)
- Growth delay (HP:0001510): A deficiency or slowing down of growth pre- and postnatally. Evidence: IEA. (OMIM:250800)
- 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:250800)
- Tremor (HP:0001337): An unintentional, oscillating to-and-fro muscle movement about a joint axis. Evidence: PCS. Frequency: 1/1. (PMID:8874222)
- Exertional dyspnea (HP:0002875): Perceived difficulty to breathe that occurs with exercise or exertion and improves with rest. Evidence: TAS. (OMIM:250800)
These phenotypes are associated with the disease methemoglobinemia due to deficiency of methemoglobin reductase (OMIM:250800).