Clinical variability of type 1 neurofibromatosis: is there a neurofibromatosis-Noonan syndrome?

A Novel Heterozygous NF1 Variant in a Neurofibromatosis-Noonan Syndrome Patient with Growth Hormone Deficiency: A Case Report

Neurofibromatosis-Noonan syndrome (NFNS), a rare autosomal-dominant hereditary disease, is characterized by clinical manifestations of both neurofibromatosis type 1 (NF1) and NS. We present a case of NFNS with short stature caused by a heterozygous nonsense variant of the NF1 gene. A 12-year-old boy was admitted because of short stature, numerous café-au-lait spots, low-set and posteriorly rotated ears, sparse eyebrows, broad forehead, and inverted triangular face. Cranial and spinal magnetic resonance imaging showed abnormal nodular lesions. Molecular analysis revealed a novel heterozygous c.6189 C > G (p.(Tyr2063*)) variant in the NF1 gene. The patient was not prescribed recombinant growth hormone (GH) therapy because exogenous GH may have enlarged the abnormal skeletal lesions. During follow-up, Lisch nodules were found in the ophthalmologic examination. NFNS, a variant form of NF1, is caused by heterozygous mutations in the NF1 gene. The mechanism of GH deficiency caused by NF1 is still unclear. Whether NFNS patients should be treated with exogenous GH remains controversial.

Neurofibromatosis-Noonan Syndrome: A Possible Paradigm of the Combination of Genetic and Epigenetic Factors

Neurofibromatosis-Noonan syndrome (NFNS) is a clinical entity possessing traits of autosomal dominant disorders neurofibromatosis type 1 (NF1) and Noonan syndrome (NS). Germline mutations that disrupt the RAS/MAPK pathway are involved in the pathogenesis of both NS and NF1. In light of a studied Greek family, a new theory for etiological pathogenesis of NFNS is suggested. The NFNS phenotype may be the final result of a combination of a genetic factor (a mutation in the NF1 gene) and an environmental factor with the epigenetic effects of muscle hypotonia (such as hydantoin in the reported Greek family), causing hypoplasia of the face and micrognathia.

Growth Hormone Deficiency in a Child with Neurofibromatosis-Noonan Syndrome

Neurofibromatosis-Noonan syndrome (NFNS) is a distinct entity which shows the features of both NF1 (neurofibromatosis 1) and Noonan syndrome (NS). While growth hormone deficiency (GHD) has been relatively frequently identified in NF1 and NS patients, there is limited experience in NFNS cases. The literature includes only one case report of a NFNS patient having GHD and that report primarily focuses on the dermatological lesions that accompany the syndrome and not on growth hormone (GH) treatment. Here, we present a 13-year-old girl who had clinical features of NFNS with a mutation in the NF1 gene. The case is the first NFNS patient reported in the literature who was diagnosed to have GHD and who received GH treatment until reaching final height. The findings in this patient show that short stature is a feature of NFNS and can be caused by GHD. Patients with NFNS who show poor growth should be evaluated for GHD.

Lethal presentation of neurofibromatosis and Noonan syndrome

Neurofibromatosis type 1 and Noonan syndrome are both common genetic disorders with autosomal dominant inheritance. Similarities between neurofibromatosis type 1 and Noonan syndrome have been noted for over 20 years and patients who share symptoms of both conditions are often given the diagnosis of neurofibromatosis-Noonan syndrome (NFNS). The molecular basis of these combined phenotypes was poorly understood and controversially discussed over several decades until the discovery that the syndromes are related through disturbances of the Ras pathway. We present an infant male with coarse facial features, severe supravalvar pulmonic stenosis, automated atrial tachycardia, hypertrophic cardiomyopathy, airway compression, severe neurological involvement, and multiple complications that lead to death during early infancy. The severity of clinical presentation and significant dysmorphic features suggested the possibility of a double genetic disorder in the Ras pathway instead of NFNS. Molecular analysis showed a missense mutation in exon 25 of the NF1 gene (4288A>G, p.N1430D) and a pathogenic mutation on exon 8 (922A>G, p.N308D) of the PTPN11 gene. Cardiovascular disease has been well described in patients with Noonan syndrome with PTPN11 mutations but the role of haploinsufficiency for neurofibromin in the heart development and function is not yet well understood. Our case suggests that a double genetic defect resulting in the hypersignaling of the Ras pathway may lead to complex cardiovascular abnormalities, cardiomyopathy, refractory arrhythmia, severe neurological phenotype, and early death.

Clinical and molecular aspects of an informative family with neurofibromatosis type 1 and Noonan phenotype

Neurofibromatosis-Noonan syndrome (NFNS) has been described as a unique phenotype, combining manifestations of neurofibromatosis type 1 (NF1) and Noonan syndrome, which are separate syndromes. Potential etiologies of NFNS include a discrete syndrome of distinct etiology, co-segregation of two mutated common genes, variable clinical expressivity of NF1, and/or allelic heterogeneity. We present an informative family with an unusual NF1 mutation with variable features of NF1 and Noonan syndrome. We hypothesize that an NF1 mutant allele can lead to diagnostic manifestations of Noonan syndrome, supporting the hypothesis that NF1 allelic heterogeneity causes NFNS.

Two neurofibromatosis type 1 cases associated with rhabdomyosarcoma of bladder, one with a large deletion in the NF1 gene

Neurofibromatosis type 1 (NF1) is the most common neurogenetic disorder, affecting approximately 1 in 3,500 individuals worldwide. Mutations of the NF1 tumor suppressor gene predispose individuals to a variety of benign and malignant tumors. Rhabdomyosarcoma (RMS) is an uncommon malignant soft tissue sarcoma and is also a rare tumor type in NF1 patients. We report two cases of NF1 with RMS. The first is that of an infant with overlapping phenotypic features of NF1 and Noonan syndrome (NS) who presented with RMS of the bladder. The second infant likewise exhibited NF1 features and was also associated with bladder RMS. DNA samples were extracted from peripheral blood and tumor tissue samples. We performed loss of heterozygosity (LOH) analysis of the NF1 gene by using seven intragenic markers (IVS27AAAT2.1, IVS27EVI-20, IVS27AC24.8, IVS27AC28.4, M98509, IVS27AC33.1, IVS38TG53.0) and one extragenic polymorphic marker (3'NF1). A large deletion was detected in the NF1 gene in the NF1-Noonan syndrome (NF-NS) case associated with RMS.

A variable combination of features of Noonan syndrome and neurofibromatosis type I are caused by mutations in theNF1 gene

Signs of neurofibromatosis type 1 (NF1) and Noonan syndrome (NS), two distinct autosomal dominant disorders, occur together in patients reported as Watson syndrome (WS), neurofibromatosis-Noonan syndrome (NFNS), partial LEOPARD syndrome, NS with features of NF1, and NF1 with Noonan-like features. The molecular basis of these combined phenotypes was poorly understood and controversially discussed over several decades. Only recently, there is increasing evidence for WS and NFNS being allelic to NF1 in the majority of patients. In this study we describe seven novel patients from five unrelated families with variable phenotypes of the NF1-NS spectrum which were systematically analyzed for mutations in the disease-causing genes NF1 for NF1 and PTPN11 for NS. Heterozygous mutations or deletions of NF1 were identified in all patients, while no PTPN11 mutation was found. The NF1 mutation segregated with the phenotype in both familial cases. These results support the hypothesis that variable phenotypes of the NF1-NS spectrum represent variants of NF1 in the majority of cases. Constitutive deregulation of the Ras pathway either through activating mutations of PTPN11 or through haploinsufficiency of neurofibromin, which acts as a Ras-inactivating GTP-ase, is probably the common pathogenetic mechanism explaining the phenotypic overlap of NS and NF1.

NF1 gene mutations represent the major molecular event underlying neurofibromatosis-Noonan syndrome

Neurofibromatosis type 1 (NF1) demonstrates phenotypic overlap with Noonan syndrome (NS) in some patients, which results in the so-called neurofibromatosis-Noonan syndrome (NFNS). From a genetic point of view, NFNS is a poorly understood condition, and controversy remains as to whether it represents a variable manifestation of either NF1 or NS or is a distinct clinical entity. To answer this question, we screened a cohort with clinically well-characterized NFNS for mutations in the entire coding sequence of the NF1 and PTPN11 genes. Heterozygous NF1 defects were identified in 16 of the 17 unrelated subjects included in the study, which provides evidence that mutations in NF1 represent the major molecular event underlying this condition. Lesions included nonsense mutations, out-of-frame deletions, missense changes, small inframe deletions, and one large multiexon deletion. Remarkably, a high prevalence of inframe defects affecting exons 24 and 25, which encode a portion of the GAP-related domain of the protein, was observed. On the other hand, no defect in PTPN11 was observed, and no lesion affecting exons 11-27 of the NF1 gene was identified in 100 PTPN11 mutation-negative subjects with NS, which provides further evidence that NFNS and NS are genetically distinct disorders. These results support the view that NFNS represents a variant of NF1 and is caused by mutations of the NF1 gene, some of which have been demonstrated to cause classic NF1 in other individuals.

Neurofibromatosis--Noonan's syndrome with associated rhabdomyosarcoma of the urinary bladder in an infant: case report

Neurofibromatosis 1 is an autosomal dominant disorder. Noonan's syndrome is known to be associated with neurofibromatoses. Patients with neurofibromatosis are predisposed to developing malignant tumors. The relationship between the genetic changes in the neurofibromin gene and mechanisms associated with tumor development in neurofibromatosis has been investigated. A non-sense mutation C2446T --> R816X of the neurofibromin gene has been detected in some patients with the neurofibromatosis 1-Noonan's syndrome phenotype. We describe a case of an infant with the overlapping features of neurofibromatosis 1 and Noonan's syndrome who presented with rhabdomyosarcoma of the urinary bladder. The genetic analysis of our patient revealed neither mutation in the neurofibromatosis 1-guanosine triphosphatase-activating protein-related domain nor the R816X nonsense mutation. The phenotypic and genotypic features of neurofibromatosis, Noonan's syndrome, and cases with the overlapping features of both syndromes have been reviewed. The presentation of our case underlines the importance of careful examination for the clinical features of neurofibromatosis and phenotypic traits of associated diseases, especially in patients with malignant tumors.

Neurofibromatosis 1: clinical manifestations and diagnostic criteria

Neurofibromatosis 1 occurs in 2 to 3 people per 10,000. The most frequent clinical features are café-au-lait macules, neurofibromas, intertriginous freckling, Lisch nodules, and learning disabilities, but optic and other gliomas, malignant peripheral nerve sheath tumors, and characteristic osseous lesions also can be present. Two striking aspects of neurofibromatosis 1 are its progressive nature and its extreme variability. This article reviews the natural history and some important clinical manifestations of neurofibromatosis 1, with emphasis on features that constitute the standard diagnostic criteria. The pathogenic implications of these clinical manifestations are also considered.

Neurofibromatosis 1

Neurofibromatosis 1 is one of the most common genetic conditions affecting the nervous system. Individuals with NF1 are predisposed to the development of peripheral nerve sheath tumors (neurofibromas and MPNSTs), astrocytomas (optic pathway gliomas), learning disabilities, seizures, strokes, macrocephaly, and vascular abnormalities. The NF1 tumor suppressor gene encodes a large protein (neurofibromin) that functions primarily as a RAS negative regulator, suggesting that targeted therapy for NF1 might derive from inhibition of the RAS signaling pathway.

Chromosomal anomalies in human gametes and pre-implantation embryos, and their potential effect on reproduction

This paper reviews the latest data on chromosomal abnormalities in human gametes and embryos. A close relationship between such anomalies and reproduction failure in humans has been postulated, thereby underscoring the importance of ongoing studies into the mechanisms leading to anomalies. Until recently, knowledge of chromosomal anomalies in human gametes and embryos has been limited. Newly developed strategies (in vitro fertilization combined with micromanipulation techniques followed by multicolour fluorescence in situ hybridization, and PCR analyses) allow precise investigation of this problem. This review of the available information on the etiology of chromosomal anomalies indicates that some of the genetic anomalies in human gametes and early embryos result in reproductive failure.

Cardiovascular malformations and other cardiovascular abnormalities in neurofibromatosis 1

Although it is well recognized that a peripheral vasculopathy may occur in patients with neurofibromatosis 1 (NF1), it is unclear whether cardiovascular abnormalities are more common. We reviewed the frequency of cardiovascular abnormalities, in particular, cardiovascular malformations (CVMs), among 2322 patients with definite NF1 in the National Neurofibromatosis Foundation International Database from 1991-98. Cardiovascular malformations were reported in 54/2322 (2.3%) of the NF1 patients, only 4 of whom had Watson syndrome or NF1-Noonan syndrome. There was a predominance of Class II "flow" defects [Clark, 1995: Moss and Adams' Heart Disease in Infants, Children, and Adolescents Including the Fetus and Young Adult. p 60-70] (43/54, 80%) among the NF1 patients with CVMs. Pulmonic stenosis, that was present in 25 NF1 patients, and aortic coarctation, that occurred in 5, constitute much larger proportions of all CVMs than expected. Of interest was the paucity of Class I conotruncal defects (2 patients with tetralogy of Fallot), and the absence of atrioventricular canal, anomalous pulmonary venous return, complex single ventricle and laterality defects. Besides the 54 patients with CVMs, there were 27 patients with other cardiac abnormalities (16 with murmur, 5 with mitral valve prolapse, 1 with intracardiac tumor, and 5 with electrocardiogram abnormalities). No patient in this study had hypertrophic cardiomyopathy. There were 16 patients who had a peripheral vascular abnormality without an intracardiac CVM, plus an additional 4 patients among those with a CVM who also had a peripheral vascular abnormality.

Non-bullous congenital ichthyosiform erythroderma, with ocular albinism and Noonan syndrome

A 21-year-old woman presented with non-bullous congenital ichthyosiform erythroderma; she was born a collodion baby. Associated features were ocular albinism, anterior segment dysgenesis of both eyes and Noonan syndrome. X-linked ichthyosis (steroid sulphatase deficiency) and X-linked ocular albinism have been mapped to the Xp22.3 region and cases have been reported with both conditions due to a partial short-arm deletion of the X chromosome. The ichthyosis and ocular albinism in the present case, however, are likely to be of the autosomal recessive type - a very rare association - and the combination with Noonan syndrome has not been reported previously.

Neurofibromatosis-Noonan syndrome and acute lymphoblastic leukemia: a report of two cases

Two boys with neurofibromatosis-Noonan syndrome in whom acute lymphoblastic leukemia (ALL) developed are described. Both patients demonstrated B-lineage leukemias with normal cytogenetics. They were treated with combination chemotherapy and remain in remission off therapy. Patients with neurofibromatosis-Noonan syndrome may be at increased risk for ALL.

Neurofibromatosis type 1 (NF1): a protein truncation assay yielding identification of mutations in 73% of patients

Neurofibromatosis type 1 (NF1) is caused by mutations in a tumour suppressor gene located on chromosome 17 (17q11.2). Disease causing mutations are dispersed throughout the gene, which spans 350 kilobases and includes 59 exons. A common consequence of NF1 mutations is introduction of a premature stop codon, and the majority of mutant genes encode truncated forms of neurofibromin. We used a protein truncation assay to screen for mutations in 15 NF1 patients and obtained positive results in 11 of them (73%). Sequencing of cDNA and genomic DNA yielded identification of 10 different mutations, including four splicing errors, three small deletions, two nonsense mutations, and one small insertion. Nine mutations were predicted to cause premature termination of translation, while one mutation caused in frame deletion as a result ofexon skipping. In one other case involving abnormal splicing, five different aberrantly spliced transcripts were detected. One germline nonsense mutation (R1306X, 3916C>T) corresponded to the same base change that occurs by mRNA editing in normal subjects. The second nonsense mutation (R2496X) was the sole germline mutation that has been previously described. The subjects studied represented typically affected NF1 patients and no correlations between genotype and phenotype were apparent. A high incidence of ocular hypertelorism was observed.

Familial neurofibromatosis 1 microdeletions: cosegregation with distinct facial phenotype and early onset of cutaneous neurofibromata

A notable subset of the recent literature on the disorder neurofibromatosis type 1 (NF1) describes patients with NF1, facial anomalies, and other unusual findings. We describe a molecular re-evaluation of two such families reported previously by Kaplan and Rosenblatt [1985], who suggested that their NF1 manifestations, facial phenotype, and other findings could result from a disorder distinct from NF1. Submicroscopic deletions involving the NF1 gene were identified in both families by fluorescent in situ hybridization and analysis of somatic cell hybrids. Affected subjects of the first family were heterozygous for a microdeletion of approximately 2 Mb, which included the entire NF1 gene and flanking contiguous sequences. The family was remarkable for cosegregation of the NF1 microdeletion with facial abnormalities and a pattern of early onset of cutaneous neurofibromata upon transmission from an affected mother to her three affected children. The propositus of the second family carried a deletion that at the least involved NF1 exon 2 through intron 27, which is > 200 kilobases in length. Because all persons in the family were deceased, the size of the deletion could not be determined precisely. Facial anomalies were observed in the propositus and his NF1-affected mother and sister. The data from these families support our hypothesis, which was initially based solely on sporadic deletion cases, that deletion of the entire NF1 gene, or in conjunction with deletion of unknown contiguous genes, causes the facial anomalies and early onset of neurofibromata observed in this subset of NF1 patients. In addition, other features observed in the persons in these families suggest that some NF1 microdeletion patients may be at increased risk for connective tissue abnormalities and/or neoplasms.

Ullrich-Turner syndrome and neurofibromatosis-1

There is a well-known association between neurofibromatosis-1 (NF1) and Noonan syndrome-like manifestations, including short stature, short broad neck, and hypertelorism. These anomalies are thought to be due to variable expression of the NF1 gene. We report on two girls with NF1 who were found to have the Ullrich-Turner syndrome. Case 1, a 12-year-old white girl, was followed in a Neurofibromatosis Clinic because of multiple café-au-lait spots and a family history of NF1 in her mother and sister. On examination, she had short stature, hypertelorism, and short neck with low posterior hairline. Karyotype was 86% 46,XY/14% 45,X. Case 2, the first child of a woman with NF1, presented at birth with lymphedema of hands and feet and a short broad neck. Karyotype was 45,X. At age 23 months she was short, had epicanthic folds, hypertelorism, narrow palate, right simian crease, 19 café-au-lait spots, and axillary freckling. We conclude that chromosome studies should be performed in girls with NF1 who have short stature and Noonan- or Ullrich-Turner-like findings. Dilemmas raised by the dual diagnoses of NF1 and Ullrich-Turner syndrome include potential risks of growth hormone therapy and estrogen replacement therapy.

Exclusion of allelism of Noonan syndrome and neurofibromatosis-type 1 in a large family with Noonan syndrome-neurofibromatosis association

A large four-generation family with Noonan syndrome (NS) and neurofibromatosis-type 1 (NF1) was studied for clinical association between the two diseases and for linkage analysis with polymorphic DNA markers of the NF1 region in 17q11.2. Nonrandom segregation between NS and NF1 phenotypes was observed. Neurofibromatosis was tightly linked to NF1 markers, whereas Noonan syndrome was found not be allelic to NF1. These results suggest that two mutations at two independent but closely linked loci are the cause of neurofibromatosis-Noonan syndrome (NF-NS) association in this family.

Neurofibromatosis/Noonan phenotype: a variable feature of type 1 neurofibromatosis

Since January 1989 we have ascertained patients with neurofibromatosis type 1 (NF1) as part of our genetic register in the North West of England. This register has now identified 453 affected cases from 235 families. The first 94 individuals were specifically examined for features of the Noonan phenotype. This was present in 12/94 sequentially identified individuals with NF1 including six individuals from three families. However, three cases occurred in a further family, where Noonan syndrome appeared to segregate separately from NF1. We have provided evidence for the chance association of Noonan syndrome and NF1 and that the Noonan phenotype occurs as a feature in some NF1 families. However, there is now little evidence of a separate NF1/Noonan syndrome entity or of NF1 features occurring in classical Noonan syndrome.

Neurofibromatosis-Noonan syndrome

Type I neurofibromatosis (NF-1) and Noonan syndrome (NS) are two fairly common genetic disorders. Patients with features of both disorders have been described, but considerable variability of phenotypic expression occurs. As a result, the correct nosology of this syndrome is uncertain. We present a patient with full expression of both NF-1 and NS phenotypes, and discuss the debate regarding the genetics of the combined syndrome.

Noonan syndrome with café-au-lait spots and multiple lentigines syndrome are not linked to the neurofibromatosis type 1 locus

Noonan syndrome, multiple lentigines syndrome (LEOPARD syndrome), Watson syndrome and neurofibromatosis type 1 share certain clinical manifestations. We present a linkage analysis using microsatellite markers located in the neurofibromatosis type 1 region at 17q11 in a family with Noonan syndrome and café-au-lait spots and in another family with multiple lentigines syndrome. No linkage of the disease to the neurofibromatosis type 1 locus was found in the families investigated. On the basis of our results, we suggest that neither familial multiple lentigines syndrome nor Noonan syndrome is caused by a defect in the neurofibromatosis type 1 gene.

Noonan syndrome

The Noonan syndrome is a rare disease characterized by dysmorphic facies, short stature, ear abnormalities, cryptorchidism, ocular abnormalities, cardiovascular anomalies, cubitus valgus, webbed neck, and cutaneous and hair abnormalities. Some 25% to 40% of patients have dermatologic abnormalities. Diagnosis is purely clinical, and intrauterine diagnosis is very important based on the presence of cystic hygroma and evidence of myocardial abnormalities. Treatment is symptomatic. Genetic counseling is necessary.

Deletions spanning the neurofibromatosis 1 gene: identification and phenotype of five patients

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder characterized by marked variation in clinical severity. To investigate the contribution to variability by genes either contiguous to or contained within the NF1 gene, we screened six NF1 patients with mild facial dysmorphology, mental retardation, and/or learning disabilities, for DNA rearrangement of the NF1 region. Five of the six patients had NF1 gene deletions on the basis of quantitative densitometry, locus hemizygosity, and analysis of somatic cell hybrid lines. Analyses of hybrid lines carrying each of the patient's chromosomes 17, with 15 regional DNA markers, demonstrated that each of the five patients carried a deletion > 700 kb in size. Minimally, each of the deletions involved the entire 350-kb NF1 gene; the three genes--EVI2A, EVI2B, and OMG--that are contained within an NF1 intron; and considerable flanking DNA. For four of the patients, the deletions mapped to the same interval; the deletion in the fifth patient was larger, extending farther in both directions. The remaining NF1 allele presumably produced functional neurofibromin; no gene rearrangements were detected, and RNA-PCR demonstrated that it was transcribed. These data provide compelling evidence that the NF1 disorder results from haploid insufficiency of neurofibromin. Of the three documented de novo deletion cases, two involved the paternal NF1 allele and one the maternal allele. The parental origin of the single remaining expressed NF1 allele had no dramatic effect on patient phenotype. The deletion patients exhibited a variable number of physical anomalies that were not correlated with the extent of their deletion. All five patients with deletions were remarkable for exhibiting a large number of neurofibromas for their age, suggesting that deletion of an unknown gene in the NF1 region may affect tumor initiation or development.

Neurofibromatosis type 1: review of the first 200 patients in an Australian clinic

Neurofibromatosis type 1 is a common multisystem disorder, best managed in a multidisciplinary clinic. In 1991, the first Australian neurofibromatosis clinic was established at the Children's Hospital, Camperdown, and the clinical characteristics of the first 150 families are reviewed. Two hundred individuals were assessed; there was an equal sex distribution, and 55% of cases were sporadic. Advanced paternal age appeared to predispose to new mutations in the neurofibromatosis gene. Café-au-lait spots and axillary freckling were important to the diagnosis of neurofibromatosis type 1 during childhood, and neurofibromas and Lisch nodules, although often not appearing until after puberty, were present in almost all patients over 30 years of age. Short stature (27%), macrocephaly (43%), scoliosis (20.5%), and learning disabilities (45%) were common associated features. The prevalence of disease complications was similar to the major US and European studies.

Reproductive failure in a patient with neurofibromatosis-Noonan syndrome

We report on a 39-year-old man with neurofibromatosis-Noonan syndrome and long-standing infertility. Comprehensive testing did not uncover any significant endocrine abnormalities, but the testicular seminiferous epithelium was found to be severely compromised. While the occasional association of neurofibromatosis with signs of Noonan syndrome has been reported, reproductive failure has not been previously described in this condition.

Tandem duplication within a neurofibromatosis type 1 (NF1) gene exon in a family with features of Watson syndrome and Noonan syndrome

Type 1 neurofibromatosis (NF1), Watson syndrome (WS), and Noonan syndrome (NS) show some overlap in clinical manifestations. In addition, WS has been shown to be linked to markers flanking the NF1 locus and a deletion at the NF1 locus demonstrated in a WS patient. This suggests either that WS and NF1 are allelic or that phenotypes arise from mutations in very closely linked genes. Here we provide evidence for the former by demonstrating a mutation in the NF1 gene in a family with features of both WS and NS. The mutation is an almost perfect in-frame tandem duplication of 42 bases in exon 28 of the NF1 gene. Unlike the mutations previously described in classical NF1, which show a preponderance of null alleles, the mutation in this family would be expected to result in a mutant neurofibromin product.