Neurofibromatosis von Recklinghausen type I (NF-1) is caused by heterozygous mutation in the neurofibromin gene, located in the region 17qll.2. Etiology of NF-1 is molecular heterogenic, there are point mutations, microdeletion and mosaics, which show different manifestation of phe-notype. Many point mutations are characterized particularly by cafe-au-lait spots (6 spots at least 1.5 cm in diameter), fibromatous tumours of the skin and neurofibromas, other features such as Lisch nodules, axillary freckling, scoliosis, cardiovascular anomalies, hypertension, macrocepha-ly, short stature, precoccious puberty due to tumors of the optic chiasm are variably present. Microdeletion involving the NF-1 gene and contiguous genes lying in its flanking regions are characterized by a more severe phenotype, and the patients show facial dysmorphism, microcephaly, developmental delay and mental retardation, accelerated growth in childhood and excessive number of neurofibromas in relation to age. Segmental form shows sectorial skin features, soma-tic asymmetry and solitary occurrence in the family. Diagnostic proceduře for confirmation is different according to the etiology. Point mutations request sequencing and the detection efficacy is circa 80%. Microdeletion is the cause of 5-20% cases and is detected using in šitu hybridization with intragenic probes. Segmental form represents a somatic mutation, is found in around 10% of cases and the mutation (point or microdeletion) is identified exceptionally in cells from café au lait, neurofibroma or freckles. We refer to segmental neurofibromatosis in a young man to emphasize an importance of good clinical as well as genetic prognosis of reproduction in his family.

        Key words: neurofibromatosis type I von Recklinghausen, segmental form, postzygotic mutati¬on, somatic mosaic