Hypomelanosis of Ito
Hypomelanosis of Ito (synonym: incontinentia pigmenti achromians) is a rare, sporadic, multisystem disorder, but is the third most common neurocutaneous syndrome after neurofibromatosis type 1 and tuberous sclerosis. About 50 per cent of patients show chromosomal abnormalities, most commonly mosaicisms or translocations, but also trisomies, translocations, and point mutations (Sybert 1994). In families where there are sufficient numbers of affected individuals, genetic linkage analysis may be possible, using markers from the Xq28 region of the X chromosome (Jouet et al. 1997).
The term has been used to describe a condition where there are hypopigmented or depigmented streaks or whorls in the skin along the lines of Blaschko (Fig. 19.6a, b). The skin changes are present within the first year of life in 70 per cent of cases and the hypopigmented areas in Caucasians are best seen using Wood's light. The extent of skin changes does not correlate with the severity of the systemic disease. Over 50 per cent of patients have neurological, skeletal, or ocular abnormalities. The neurological problems are due to cerebral and cerebellar developmental abnormalities, arteriovenous malformations, or tumours (e.g. choroid plexus papilloma, medulloblastoma). The most frequent neurological abnormalities are mental retardation and seizures, thought to be related to neuroblast migrational disorders. Oral abnormalities include dental dysplasia and conical teeth. Alopecia and changes in hair colour (grey-white hair) may appear prematurely.
Diagnosis rests on possible genetic linkage analysis of the blood, or karyotyping of blood and affected skin may detect mosaicism (frequently X:autosomal translocation) (Boon et al. 1996), and the recognition of skin, nervous system, musculoskeletal, and other anomalies. EEG and MRI findings are common but non-specific. MRI abnormalities can occur in the absence of neurological signs (Steiner et al. 1996).
Management is symptomatic: anticonvulsants for seizures, perhaps steroids for infantile spasms, physiotherapy for motor difficulties, educational support for those with learning difficulties, and specialist opinion for ocular, dental, and skeletal problems. First-degree relative should be examined and genetic counselling offered to appropriate family members