A cytogenetic deletion, del(17)(q11.22q21.1), in a patient with sporadic neurofibromatosis type 1 (NF1) associated with dysmorphism and developmental delay

Nf1 in heart development: a potential causative gene for congenital heart disease: a narrative review

Congenital heart disease is the most frequent congenital disorder, affecting a significant number of live births. Gaining insights into its genetic etiology could lead to a deeper understanding of this condition. Although the Nf1 gene has been identified as a potential causative gene, its role in congenital heart disease has not been thoroughly clarified. We searched and summarized evidence from cohort-based and experimental studies on the issue of Nf1 and heart development in congenital heart diseases from various databases. Available evidence demonstrates a correlation between Nf1 and congenital heart diseases, mainly pulmonary valvar stenosis. The mechanism underlying this correlation may involve dysregulation of epithelial-mesenchymal transition (EMT). The Nf1 gene affects the EMT process via multiple pathways, including directly regulating the expression of EMT-related transcription factors and indirectly regulating the EMT process by regulating the MAPK pathway. This narrative review provides a comprehensive account of the Nf1 involvement in heart development and congenital cardiovascular diseases in terms of epidemiology and potential mechanisms. RAS signaling may contribute to congenital heart disease independently or in cooperation with other signaling pathways. Efficient management of both NF1 and cardiovascular disease patients would benefit from further research into these issues.

Atypical NF1 Microdeletions: Challenges and Opportunities for Genotype/Phenotype Correlations in Patients with Large NF1 Deletions

Patients with neurofibromatosis type 1 (NF1) and type 1 NF1 deletions often exhibit more severe clinical manifestations than patients with intragenic NF1 gene mutations, including facial dysmorphic features, overgrowth, severe global developmental delay, severe autistic symptoms and considerably reduced cognitive abilities, all of which are detectable from a very young age. Type 1 NF1 deletions encompass 1.4 Mb and are associated with the loss of 14 protein-coding genes, including NF1 and SUZ12. Atypical NF1 deletions, which do not encompass all 14 protein-coding genes located within the type 1 NF1 deletion region, have the potential to contribute to the delineation of the genotype/phenotype relationship in patients with NF1 microdeletions. Here, we review all atypical NF1 deletions reported to date as well as the clinical phenotype observed in the patients concerned. We compare these findings with those of a newly identified atypical NF1 deletion of 698 kb which, in addition to the NF1 gene, includes five genes located centromeric to NF1. The atypical NF1 deletion in this patient does not include the SUZ12 gene but does encompass CRLF3. Comparative analysis of such atypical NF1 deletions suggests that SUZ12 hemizygosity is likely to contribute significantly to the reduced cognitive abilities, severe global developmental delay and facial dysmorphisms observed in patients with type 1 NF1 deletions.

Genotype-Phenotype Associations in Patients With Type-1, Type-2, and Atypical NF1 Microdeletions

Neurofibromatosis type 1 is a tumor predisposition syndrome inherited in autosomal dominant manner. Besides the intragenic loss-of-function mutations in NF1 gene, large deletions encompassing the NF1 gene and its flanking regions are responsible for the development of the variable clinical phenotype. These large deletions titled as NF1 microdeletions lead to a more severe clinical phenotype than those observed in patients with intragenic NF1 mutations. Around 5-10% of the cases harbor large deletion and four major types of NF1 microdeletions (type 1, 2, 3 and atypical) have been identified so far. They are distinguishable in term of their size and the location of the breakpoints, by the frequency of somatic mosaicism with normal cells not harboring the deletion and by the number of the affected genes within the deleted region. In our study genotype-phenotype analyses have been performed in 17 mostly pediatric patients with NF1 microdeletion syndrome identified by multiplex ligation-dependent probe amplification after systematic sequencing of the NF1 gene. Confirmation and classification of the NF1 large deletions were performed using array comparative genomic hybridization, where it was feasible. In our patient cohort 70% of the patients possess type-1 deletion, one patient harbors type-2 deletion and 23% of our cases have atypical NF1 deletion. All the atypical deletions identified in this study proved to be novel. One patient with atypical deletion displayed mosaicism. In our study NF1 microdeletion patients presented dysmorphic facial features, macrocephaly, large hands and feet, delayed cognitive development and/or learning difficulties, speech difficulties, overgrowth more often than patients with intragenic NF1 mutations. Moreover, neurobehavior problems, macrocephaly and overgrowth were less frequent in atypical cases compared to type-1 deletion. Proper diagnosis is challenging in certain patients since several clinical manifestations show age-dependency. Large tumor load exhibited more frequently in this type of disorder, therefore better understanding of genotype-phenotype correlations and progress of the disease is essential for individuals suffering from neurofibromatosis to improve the quality of their life. Our study presented additional clinical data related to NF1 microdeletion patients especially for pediatric cases and it contributes to the better understanding of this type of disorder.

Emerging genotype-phenotype relationships in patients with large NF1 deletions

The most frequent recurring mutations in neurofibromatosis type 1 (NF1) are large deletions encompassing the NF1 gene and its flanking regions (NF1 microdeletions). The majority of these deletions encompass 1.4-Mb and are associated with the loss of 14 protein-coding genes and four microRNA genes. Patients with germline type-1 NF1 microdeletions frequently exhibit dysmorphic facial features, overgrowth/tall-for-age stature, significant delay in cognitive development, large hands and feet, hyperflexibility of joints and muscular hypotonia. Such patients also display significantly more cardiovascular anomalies as compared with patients without large deletions and often exhibit increased numbers of subcutaneous, plexiform and spinal neurofibromas as compared with the general NF1 population. Further, an extremely high burden of internal neurofibromas, characterised by >3000 ml tumour volume, is encountered significantly, more frequently, in non-mosaic NF1 microdeletion patients than in NF1 patients lacking such deletions. NF1 microdeletion patients also have an increased risk of malignant peripheral nerve sheath tumours (MPNSTs); their lifetime MPNST risk is 16–26%, rather higher than that of NF1 patients with intragenic NF1 mutations (8–13%). NF1 microdeletion patients, therefore, represent a high-risk group for the development of MPNSTs, tumours which are very aggressive and difficult to treat. Co-deletion of the SUZ12 gene in addition to NF1 further increases the MPNST risk in NF1 microdeletion patients. Here, we summarise current knowledge about genotype–phenotype relationships in NF1 microdeletion patients and discuss the potential role of the genes located within the NF1 microdeletion interval whose haploinsufficiency may contribute to the more severe clinical phenotype.

Coexistence of multiple rare spinal abnormalities in type 1 neurofibromatosis: a case report and literature review

Orthopaedic involvement is the most common clinical presentation of Neurofibromatosis type 1 (NF-1) patients with the spinal abnormalities more frequently affected. In the spinal deformities of NF-1 patients, despite the scoliosis is the most frequent finding, several distinctive radiographic features, such as dural ectasia, defective pedicles, and spondylolisthesis, are relatively less common. Here, we reported a 16-year-old boy diagnosed with NF-1 who presented with dural ectasia, defective pedicles, and spondylolisthesis concomitantly, described the surgical treatment and provided a literature review. The boy complained of low back and leg pain for two months. On clinical examination, the patient showed multiple café au lait spots on his back and no neurological deficit. He had a family history of neurofibromatosis as his father suffering from NF-1. Imaging results demonstrated mild scoliosis, posterior scalloping of the lumber spine, L5 spondylolisthesis on plain radiographs, and marked dural ectasia of L3-L5 on MRI. Furthermore, the CT scan showed presence of thin pedicles at L3, bilateral symmetrical pedicle clefts at L4, and pars interarticularis fractures at L5. The patient received a long level posterior fusion from L1 to S1 with pedicle screws. Iliac crest autogenous graft mixed with artificial bone were used to achieve solid arthrodesis. At nine-month follow-up, the patient was asymptomatic and able to live a normal life. Our observation demonstrated that familiarity with those distinctive features in NF-1 patients could be contributed to making an early diagnosis and optimizing treatment.

Mice lacking Nf1 in osteochondroprogenitor cells display skeletal dysplasia similar to patients with neurofibromatosis type I

Mutations in NF1 cause neurofibromatosis type I (NF1), a disorder characterized, among other clinical manifestations, by generalized and focal bony lesions. Dystrophic scoliosis and tibial pseudoarthrosis are the most severe skeletal manifestations for which treatment is not satisfactory, emphasizing the dearth of knowledge related to the biology of NF1 in bone cells. Using reporter mice, we report here that the mouse Col2α1-Cre promoter (collagen, type II, alpha 1) is active not only in chondrocytes but also in adult bone marrow osteoprogenitors giving rise to osteoblasts. Based on this finding, we crossed the Col2α1-Cre transgenic and Nf1(flox/flox) mice to determine whether loss of Nf1 in axial and appendicular osteochondroprogenitors recapitulates the skeletal abnormalities of NF1 patients. By microtomographic and X-rays studies, we show that Nf1(Col2)(-/-) mice display progressive scoliosis and kyphosis, tibial bowing and abnormalities in skull and anterior chest wall formation. These defects were accompanied by a low bone mass phenotype, high bone cortical porosity, osteoidosis, increased osteoclastogenesis and decreased osteoblast number, as quantified by histomorphometry and 3D-microtomography. Loss of Nf1 in osteochondroprogenitors also caused severe short stature and intervertebral disc defects. Blockade of the RAS/ERK activation characteristic of Nf1(-/-) osteoprogenitors by lovastatin during embryonic development could attenuate the increased cortical porosity observed in mutant pups. These data and the skeletal similarities between this mouse model and NF1 patients thus suggest that activation of the RAS/ERK pathway by Nf1 loss-of-function in osteochondroprogenitors is responsible for the vertebral and tibia lesions in NF1 patients, and that this molecular signature may represent a good therapeutic target.

Orthopaedic manifestations of neurofibromatosis type 1

Neurofibromatosis type 1 (NF-1) is an autosomal dominant disease that affects 1 in 3,000 persons worldwide. Café-au-lait macules and peripheral nerve sheath tumors (ie, neurofibromas) are the most commonly recognized manifestations of NF-1. However, NF-1 affects multiple organ systems, and a multidisciplinary approach to treatment is required. Management of the orthopaedic manifestations of NF-1 is often difficult. The most complex manifestations are scoliosis (dystrophic and nondystrophic), congenital pseudarthrosis of the tibia, and problems related to soft-tissue tumors. Metabolic bone disease is common; many patients are frankly osteopenic, which further complicates treatment. Dystrophic scoliosis, which may be caused by either bony dysplasia or intraspinal pathology, is characterized by early presentation and rapid progression. Pseudarthrosis is common even after instrumented fusion. Nondystrophic scoliosis tends to behave like adolescent idiopathic scoliosis, although it may present earlier and is associated with a higher rate of pseudarthrosis. Congenital pseudarthrosis of the tibia is a long-bone dysplasia that afflicts patients with NF-1. Management of this osseous deformity is challenging. Failure to achieve union and refracture are common.

Characterization of a 7.6-Mb germline deletion encompassing the NF1 locus and about a hundred genes in an NF1 contiguous gene syndrome patient

We describe a large germline deletion removing the NF1 locus, identified by heterozygosity mapping based on microsatellite markers, in an 8-year-old French girl with a particularly severe NF1 contiguous gene syndrome. We used gene-dose mapping with sequence-tagged site real-time PCR to locate the deletion end points, which were precisely characterized by means of long-range PCR and nucleotide sequencing. The deletion is located on chromosome arm 17q and is exactly 7 586 986 bp long. It encompasses the entire NF1 locus and about 100 other genes, including numerous chemokine genes, an attractive in silico-selected cerebrally expressed candidate gene (designated NUFIP2, for nuclear fragile X mental retardation protein interacting protein 2; NM_020772) and four microRNA genes. Interestingly, the centromeric breakpoint is located in intron 4 of the PIPOX gene (pipecolic acid oxidase; NM_016518) and the telomeric breakpoint in intron 5 of the GGNBP2 gene (gametogenetin binding protein 2; NM_024835) coding a transcription factor. As PIPOX and GGNBP2 have the same transcriptional orientation, we postulated, and then confirmed, the existence of a chimeric transcript. This transcript, and/or haploinsufficiency of one or several deleted genes, could explain the clinical severity of the syndrome in this patient.

Absence of cutaneous neurofibromas in an NF1 patient with an atypical deletion partially overlapping the common 1.4 Mb microdeleted region

The majority of neurofibromatosis type 1 (NF1) microdeletions in 17q11.2 span approximately 1.4 Mb and have breakpoints that lie within the proximal and distal NF1-low copy repeats, termed NF1-REPs. Less frequent are patients with atypical deletions and non-recurring breakpoints. NF1 patients with gross deletions have been reported to manifest a more severe clinical phenotype than NF1 patients with intragenic mutations, and display early onset and extensive growth of neurofibromas. It has been suggested that the deletion of a neighboring gene or genes in addition to the NF1 gene may modify the expression of the disease, particularly with regard to the high burden of cutaneous neurofibromas. Thus, atypical deletions partially overlapping with the common 1.4 Mb microdeletion interval could prove useful in identifying possible genetic modifiers in the NF1 gene region whose haploinsufficiency might promote neurofibroma growth. Here we report a 20-year-old female who has an atypical deletion with a proximal breakpoint in NF1 intron 21 and a distal deletion breakpoint in the ACCN1 gene. The deletion spans 2.7 Mb and was mediated by an intrachromosomal non-homology-driven mechanism, for example, non-homologous end-joining (NHEJ). Remarkably, this patient did not exhibit cutaneous neurofibromas. However, genotype-phenotype comparisons in this and other previously reported patients with atypical deletions partially overlapping the commonly deleted 1.4 Mb interval do not identify a specific deleted region that is associated with increased neurofibroma growth.

Connective tissue dysplasia in five new patients with NF1 microdeletions: further expansion of phenotype and review of the literature

Approximately 5% of patients with neurofibromatosis type 1 (NF1) have deletions of the entire NF1 gene. The phenotype usually includes early onset, large number of neurofibromas, presence of congenital anomalies, cognitive deficiency, and variable dysmorphic features and growth abnormalities. Connective tissue abnormalities are not generally recognised as a part of NF1 microdeletion syndrome, but mitral valve prolapse, joint laxity, and/or soft skin on the palms have been reported in a few patients. We describe clinical findings in six newly diagnosed patients with NF1 microdeletions, five of whom presented with connective tissue abnormalities. A literature review of the clinical findings associated with NF1 microdeletion was also performed. Our report confirms that connective tissue dysplasia is common in patients with NF1 microdeletions. Given the potential for associated cardiac manifestation, screening by echocardiogram may be warranted. Despite the large number (>150) of patients with known NF1 microdeletions, the clinical phenotype remains incompletely defined. Additional reports of patients with NF1 microdeletions, including comprehensive clinical and molecular information, are needed to elucidate possible genotype-phenotype correlation.

Familial adenomatous polyposis and mental retardation caused by a de novo chromosomal deletion at 5q15-q22: report of a case

Familial adenomatous polyposis, caused by mutations in the adenomatous polyposis coli gene located at chromosome 5q21, is an autosomal dominant syndrome characterized by polyposis of the colon and rectum and nearly 100 percent progression to colorectal cancer. We report a case of familial adenomatous polyposis and mental retardation caused by a chromosomal deletion at 5q15-q22. Chromosomal analysis is considered part of the evaluation of children with mental retardation and developmental delay. The resulting karyotypes from high-resolution chromosomal analysis can help characterize large deletions, some of which involve known tumor suppressor genes. Because familial adenomatous polyposis may arise from de novo chromosomal deletions involving the adenomatous polyposis coli gene locus, individuals with chromosomal deletions involving 5q21 should be considered at-risk for familial adenomatous polyposis and offered standard screening with flexible sigmoidoscopy by 10 to 12 years of age.

Genetic disorders of pigmentation

More than 127 loci are actually known to affect pigmentation in mouse when they are mutated. From embryogenesis to transfer of melanin to the keratinocytes or melanocytes survival, any defect is able to alter the pigmentation process. Many gene mutations are now described, but the function of their product protein and their implication in melanogenesis are only partially understood. Each genetic pigmentation disorder brings new clues in the understanding of the pigmentation process. According to the main genodermatoses known to induce hypo- or hyperpigmentation, we emphasize in this review the last advances in the understanding of the physiopathology of these diseases and try to connect, when possible, the mutation to the clinical phenotype.

Identification of novel deletion breakpoints bordered by segmental duplications in the NF1 locus using high resolution array-CGH

BACKGROUND

Segmental duplications flanking the neurofibromatosis type 1 (NF1) gene locus on 17q11 mediate most gene deletions in NF1 patients. However, the large size of the gene and the complexity of the locus architecture pose difficulties in deletion analysis. We report the construction and application of the first NF1 locus specific microarray, covering 2.24 Mb of 17q11, using a non-redundant approach for array design. The average resolution of analysis for the array is approximately 12 kb per measurement point with an increased average resolution of 6.4 kb for the NF1 gene.

METHODS

We performed a comprehensive array-CGH analysis of 161 NF1 derived samples and identified heterozygous deletions of various sizes in 39 cases. The typical deletion was identified in 26 cases, whereas 13 samples showed atypical deletion profiles.

RESULTS

The size of the atypical deletions, contained within the segment covered by the array, ranged from 6 kb to 1.6 Mb and their breakpoints could be accurately determined. Moreover, 10 atypical deletions were observed to share a common breakpoint either on the proximal or distal end of the deletion. The deletions identified by array-CGH were independently confirmed using multiplex ligation-dependent probe amplification. Bioinformatic analysis of the entire locus identified 33 segmental duplications.

CONCLUSIONS

We show that at least one of these segmental duplications, which borders the proximal breakpoint located within the NF1 intron 1 in five atypical deletions, might represent a novel hot spot for deletions. Our array constitutes a novel and reliable tool offering significantly improved diagnostics for this common disorder.

Childhood overgrowth in patients with common NF1 microdeletions

While growth retardation and short stature are well-known features of patients with classical neurofibromatosis type 1 (NF1), we found advanced height growth and accelerated carpal bone age in patients with an NF1 microdeletion. Our analysis is based on growth data of 21 patients with common 1.4/1.2 Mb microdeletions, including three patients with a Weaver-like appearance. Overgrowth was most evident in preschool children (2-6 years, n=10, P=0.02). We conclude that childhood overgrowth is part of the phenotypic spectrum in patients with the common 1.4/1.2 Mb NF1 microdeletions and assume that the chromosomal region comprised by the microdeletions contains a gene whose haploinsufficiency causes overgrowth.

Extensively high load of internal tumors determined by whole body MRI scanning in a patient with neurofibromatosis type 1 and a non-LCR-mediated 2-Mb deletion in 17q11.2

Deletions in 17q11.2 affecting the NF1 gene and surrounding regions occur in 5% of patients with NF1. The two major types of NF1 deletions encompass 1.4-Mb and 1.2-Mb, respectively, and have breakpoints in the NF1 low-copy repeats or in the JJAZ gene and its pseudogene. Deletions larger than 1.4-Mb are rare, and only seven cases have been reported so far. Here, we describe a 26-year-old NF1 patient with an "atypical" NF1 deletion of 2-Mb. In contrast to the 1.4-Mb deletions, which preferentially occur by interchromosomal recombination during maternal meiosis, the deletion described here occurred intrachromosomally on the paternal chromosome. The centromeric deletion breakpoint lies in an L1-element located 1.3-Mb proximal to the NF1 gene. The telomeric deletion boundary is located in a single copy segment between an AT-rich segment and an AluSx-element in intron 15 of the JJAZ1 gene. Structural analysis implies that non-B DNA conformations at the breakpoints destabilized the duplex DNA and caused double-strand breaks. Although the breakpoints of this 2-Mb deletion are not recurrent, it is conspicuous that one breakpoint is located in the JJAZ1 gene. Paralogous recombination between the JJAZ1 gene and its pseudogene causes the recurrent 1.2 Mb deletions. The genomic architecture of the NF1 gene region, influenced by paralogous sequences such as the JJAZ1 gene and its pseudogene, seems also to stimulate the occurrence of non-recurrent deletions mediated by non-homologous end joining. Patient 442 described here suffers from a very high burden of subdermal neurofibromas. Magnetic resonance imaging of the whole body revealed numerous internal tumors, mainly plexiform neurofibromas and spinal tumors. This demonstrates the value of whole-body MRI scanning in determining the total tumor load, which is an important aspect in genotype/phenotype correlations with regard to large NF1 deletions.

A common set of at least 11 functional genes is lost in the majority of NF1 patients with gross deletions

Large deletions of the NF1 locus occur in 5 to 10% of patients with neurofibromatosis and are commonly associated with specific additional abnormalities characterized by mental retardation, dysmorphic features, and intellectual impairment. To characterize the extent of codeleted genes we constructed a long-range physical BAC/PAC map around the NF1 locus between D17S117 and D17S57 and determined the deletion boundaries in seven unrelated patients. Surprisingly, the proximal and distal breakpoints in five of seven patients fall at almost identical positions, resulting in the loss of at least 11 functional genes. Five of six patients investigated showed a de novo deletion on the maternally derived chromosome. Since D17S117 and D17S57 were previously reported as the outer limits for the great majority of NF1 deletions, we suggest that most NF1 patients with deletion of the entire NF1 gene are hemizygous for the same set of at least 10 additional genes, including SHGC-37343, SHGC-2390, SHGC-34232, OMG, EVI2B, EVI2A, WI-9521, WI-6742, SHGC-34334, and KIAA0160, and thus present with a relatively uniform clinical phenotype.

NF1 microdeletion syndrome: refined FISH characterization of sporadic and familial deletions with locus-specific probes

Two familial and seven sporadic patients with neurofibromatosis 1-who showed dysmorphism, learning disabilities/mental retardation, and additional signs and carried deletions of the NF1 gene-were investigated by use of a two-step FISH approach to characterize the deletions. With FISH of YAC clones belonging to a 7-Mb 17q11.2 contig, we estimated the extension of all of the deletions and identified the genomic regions harboring the breakpoints. Mosaicism accounted for the mild phenotype in two patients. In subsequent FISH experiments, performed with locus-specific probes generated from the same YACs by means of a novel procedure, we identified the smallest region of overlapping (SRO), mapped the deletion breakpoints, and identified the genes that map to each deletion interval. From centromere to telomere, the approximately 0.8-Mb SRO includes sequence-tagged site 64381, the SUPT6H gene (encoding a transcription factor involved in chromatin structure), and NF1. Extending telomerically from the SRO, two additional genes-BLMH, encoding a hydrolase involved in bleomycin resistance, and ACCN1, encoding an amiloride-sensitive cation channel expressed in the CNS-were located in the deleted intervals of seven and three patients, respectively. An apparently common centromeric deletion breakpoint was shared by all of the patients, whereas a different telomeric breakpoint defined a deletion interval of 0.8-3 Mb. There was no apparent correlation between the extent of the deletion and the phenotype. This characterization of gross NF1 deletions provides the premise for addressing correctly any genotype-phenotype correlation in the subset of patients with NF1 deletions.

A clinical variant of neurofibromatosis type 1: familial spinal neurofibromatosis with a frameshift mutation in the NF1 gene

Spinal neurofibromatosis (SNF) has been considered to be an alternative form of neurofibromatosis in which spinal cord tumors are the main clinical characteristic. Familial SNF has been reported, elsewhere, in three families-two linked to markers within the gene for neurofibromatosis type 1 (NF1) and the other not linked to NF1-but no molecular alterations have been described in these families. We describe a three-generation family that includes five members affected by SNF. All the affected members presented multiple spinal neurofibromas and café au lait spots, one member had cutaneous neurofibromas, and some members had other signs of NF1. Genetic analysis, performed with markers within and flanking the NF1 gene, showed segregation with the NF1 locus. Mutation analysis, performed with the protein-truncation test and SSCP/heteroduplex analysis of the whole coding region of the NF1 gene, identified a frameshift mutation (8042insA) in exon 46, which should result in a truncated NF1 protein. The 8042insA mutation was detected in all five family members with the SNF/NF1 phenotype. To our knowledge, this is the first time that a mutation in the NF1 gene has been associated with SNF. The clinical homogeneity in the severity of the disease among the affected members of the family, which is unusual in NF1, suggests that a particular property of the NF1 mutation described here, a gene closely linked to NF1, or posttranscriptional events are involved in this severe neurological phenotype.

Do NF1 gene deletions result in a characteristic phenotype?

Neurofibromatosis-1 (NF1) is an autosomal dominant disorder with marked variability of expression. Analysis of the NF1 gene (NF1) has detected a variety of mutations without any clear correlation with phenotype. However, deletions which remove all of NF1 have been reported in a small number of patients who have minor facial abnormalities, mental retardation, learning disabilities, and early or excessive burden of cutaneous or plexiform neurofibromas. The purpose of this study was to determine whether these phenotypic traits are associated with whole gene deletions. Out of 406 of our NF1 patients, 70 patients had manifestations previously associated with gene deletions. Thirty-five of these patients from 26 families were available for study. By fluorescence in situ hybridization (FISH) analysis, 4 were found to have deletions of the entire gene, including 2 sporadic cases, 1 familial case, and 1 case where family history could not be verified. In addition, the mother of the familial case was found to be mosaic for the deletion. Our results suggest that although large NF1 deletions occur with relatively high frequency in patients with certain findings, the presence of a deletion cannot be predicted solely on the basis of clinical phenotype.