- Melanoma (HP:0002861): The presence of a melanoma, a malignant cancer originating from pigment producing melanocytes. Melanoma can originate from the skin or the pigmented layers of the eye (the uvea). Evidence: IEA. (OMIM:249400)
- Cranial nerve paralysis (HP:0006824). Evidence: IEA. (OMIM:249400)
- Typified by somatic mosaicism (HP:0001442): Description of conditions in which affected individuals typically display somatic mosaicism, i.e., genetically distinct populations of somatic cells in a given organism caused by DNA mutations, epigenetic alterations of DNA, chromosomal abnormalities or the spontaneous reversion of inherited mutations. In many conditions typified by somatic mosaicism, constitutive mutation is lethal and cases are exclusively or predominantly mosaic. Evidence: PCS. (PMID:23392294)
- 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: IEA. (OMIM:249400)
- Syringomyelia (HP:0003396): Dilated, glial-lined cavity in spinal cord. This cavity does not communicate with the central canal, and usually is between the dorsal columns unilaterally or bilaterally along the side of the cord. Evidence: TAS. Frequency: Occasional (HP:0040283). (OMIM:249400)
- 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: Occasional (HP:0040283). (OMIM:249400)
- Arachnoid cyst (HP:0100702): An extra-parenchymal and intra-arachnoidal collection of fluid with a composition similar to that of cerebrospinal fluid. Evidence: TAS. Frequency: Occasional (HP:0040283). (OMIM:249400)
- Meningioma (HP:0002858): The presence of a meningioma, i.e., a benign tumor originating from the dura mater or arachnoid mater. Evidence: TAS. Frequency: Occasional (HP:0040283). (OMIM:249400)
- Dandy-Walker malformation (HP:0001305): A congenital brain malformation typically characterized by incomplete formation of the cerebellar vermis, dilation of the fourth ventricle, and enlargement of the posterior fossa. In layman's terms, Dandy Walker malformation is a cyst in the cerebellum (typically symmetrical) that is involved with the fourth ventricle. This may interfere with the ability to drain cerebrospinal fluid from the brain, resulting in hydrocephalus. Dandy Walker cysts are formed during early embryonic development, while the brain forms. The cyst in the cerebellum typically has several blood vessels running through it connecting to the brain, thereby prohibiting surgical removal. Evidence: TAS. Frequency: Occasional (HP:0040283). (OMIM:249400)
- 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). (OMIM:249400)
- Sporadic (HP:0003745): Cases of the disease in question occur without a previous family history, i.e., as isolated cases without being transmitted from a parent and without other siblings being affected. Evidence: IEA. (OMIM:249400)
- Death in infancy (HP:0001522): Death within the first 24 months of life. Evidence: IEA. (OMIM:249400)
- Choroid plexus papilloma (HP:0200022): Choroid plexus papilloma is a histologically benign neoplasm located in the ventricular system of the choroid plexus. Evidence: TAS. Frequency: Occasional (HP:0040283). (OMIM:249400)
- Mental deterioration (HP:0001268): Loss of previously present mental abilities, generally in adults. Evidence: IEA. (OMIM:249400)
- Numerous congenital melanocytic nevi (HP:0005603). Evidence: TAS. (OMIM:249400)
These phenotypes are associated with the disease neurocutaneous melanocytosis (OMIM:249400).