Overview of clinical cytogenetics

This unit provides an introduction to clinical cytogenetics. It opens with indications for prenatal and postnatal chromosome analysis, followed by a brief discussion of the applications of fluorescence in situ hybridization (FISH). It suggests tissue sources for prenatal and postnatal analysis, and closes with a review of numerical and structural chromosome abnormalities. This unit provides an introduction to clinical cytogenetics.

NF1 plexiform neurofibroma growth rate by volumetric MRI: Relationship to age and body weight

OBJECTIVE

To longitudinally analyze changes in plexiform neurofibroma (PN) volume in relation to age and body growth in children and young adults with neurofibromatosis type 1 and inoperable, symptomatic, or progressive PNs, using a sensitive, automated method of volumetric MRI analysis.

METHODS

We included patients 25 years of age and younger with PNs entered in a natural history study or in treatment trials who had volumetric MRI over > or =16 months.

RESULTS

We studied 49 patients (median age 8.3 years) with 61 PNs and a median evaluation period of 34 months (range 18 to 70). The PN growth rates varied among patients, but were constant within patients. Thirty-four patients (69%) experienced > or =20% increase in PN volume during the observation period. PN volume increased more rapidly than body weight over time (p = 0.026). Younger patients had the most rapid PN growth rate.

CONCLUSIONS

Volume increase of plexiform neurofibromas is a realistic and meaningful trial endpoint. In most patients plexiform neurofibroma growth rate exceeded body growth rate. The youngest patients had the fastest plexiform neurofibroma growth rate, and clinical drug development should be directed toward this population. Age stratification for clinical trials for plexiform neurofibromas should be considered.

Connexin 26 studies in patients with sensorineural hearing loss

OBJECTIVE

To determine the spectrum of connexin 26 (Cx26) mutations and their phenotypes in children with sensorineural hearing loss (SNHL) or mixed hearing loss (MHL).

DESIGN

Children with SNHL or MHL were prospectively tested for mutations in the entire coding region of the Cx26 gene.

PATIENTS

Children with SNHL or MHL with no obvious etiology for the hearing loss.

RESULTS

Between December 1, 1998, and July 1, 2000, 107 patients with SNHL or MHL from 99 families underwent Cx26 testing. Most patients were aged 1 week to 16 years (61 boys and 46 girls). Thirty (30%) of 99 probands had Cx26 mutations: biallelic mutations were detected in 18 (9 homozygous and 9 compound heterozygous) and single mutations were detected in 12. Twelve previously reported mutations (35delG, 167delT, E47X, L90P, M34T, G12V, V37I, R143W, V84L, V153I, V27I, and 310del14) and 3 novel mutations (E129K, T8M, and N206S) were found. Hearing loss in patients with biallelic Cx26 mutations ranged from unilateral high frequency to bilateral profound. Four children, 2 with biallelic mutations, had temporal bone abnormalities.

CONCLUSIONS

Connexin 26 mutations are common in children with SNHL, and it is likely that the homozygous and compound heterozygous mutations cause the SNHL. However, pathogenicity is less certain when only a single Cx26 mutation is present. Patients with biallelic Cx26 mutations had a slightly higher incidence of milder hearing loss than in previous studies. Children with SNHL or MHL should be tested for Cx26 mutations early in their evaluation.

Townes-Brocks syndrome versus expanded spectrum hemifacial microsomia: review of eight patients and further evidence of a "hot spot" for mutation in the SALL1 gene

PURPOSE

It can be difficult to differentiate clinically between hemifacial microsomia (HFM) and Townes-Brocks syndrome (TBS). The distinction is important because TBS is inherited as an autosomal dominant trait, whereas HFM is sporadic.

METHODS

We performed a retrospective analysis of eight patients with HFM-expanded spectrum and anal anomalies to determine whether this subset has TBS.

RESULTS

Two patients had major phenotypic findings of TBS. Sequencing of SALL1, the gene mutated in TBS, in four of the eight patients revealed one with a C --> T transition (resulting in a nonsense mutation R276X) at a previously identified mutational "hot spot."

CONCLUSION

Patients with overlapping features of both syndromes should be screened for SALL1 mutations.

Diagnosis and management of neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder whose major feature is the occurrence of multiple neurofibromas, which are benign tumors of the nerve sheath. It affects an estimated one in 3000 to 4000 individuals. In addition to neurofibromas, there are many other clinical manifestations, including malignant tumors such as gliomas or malignant peripheral nerve sheath tumors, and nontumor effects such as skeletal dysplasia and learning disability. Diagnosis is established on the basis of clinical criteria. Molecular genetic testing is feasible, but the large size of the gene and wide range of pathogenic mutations have so far impeded the development of a clinical diagnostic test. Insights into pathogenesis have followed from identification of the NF1 gene and the development of animal models. The major function of the gene product appears to be regulation of the ras protein. Tumors are believed to arise by the loss of function of the NF1 protein, suggesting that NF1 behaves as a tumor suppressor gene. Heterozygous effects on some cell types are also likely, however. The role of ras in the pathogenesis of tumors in NF1 has suggested an approach to treatment using ras inhibitors, some of which are likely to begin in clinical trials in NF1 patients in the near future.

Malignancy in neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) represents a major risk factor for development of malignancy, particularly malignant peripheral nerve sheath tumors (MPNST), optic gliomas, other gliomas, and leukemias. The oncologist will see NF1 patients referred for treatment of malignancy, and should be alert to the possibility of undiagnosed NF1 among patients with cancer. Brain tumors tend to have a more indolent course in NF1 than in the general population, and hence are best managed conservatively. MPNST, in contrast, do not respond to standard chemotherapy or radiation therapy. The most effective treatment of MPNST appears to be early diagnosis and surgery, but early diagnosis is hampered by frequent occurrence within preexisting large tumors, making new growth or change difficult to detect. New insights into pathogenesis now offer hope of development of specific methods of treatment with reduced toxicity and more precise molecular targeting. There is an urgent need, however, to develop methods to measure tumor growth and monitor outcomes, develop preclinical drug screening systems, and further explore the pathogenesis of the disorder to determine whether mechanisms other than Ras regulation may be important in pathogenesis.

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.

Discordant phenotype in monozygotic twins with Fryns syndrome

We report on a pair of monozygotic twins with Fryns syndrome discordant for severity of diaphragmatic defect. Both twins had macrocephaly, "coarse" facial appearance, hypoplasia of distal phalanges, and an extra pair of ribs. Twin A lacked an apparent diaphragmatic defect, and at 1 year of age had mild developmental delay. Twin B had a left congenital diaphragmatic hernia and died neonatally. Absence of diaphragmatic defect in Fryns syndrome may represent a subpopulation of more mildly affected patients whose developmental outcome is currently undetermined.

Medical education in the 'postgenomic era'

The sequence of the human genome is very nearly in hand; the first draft has been completed, and the finished sequence will be available years ahead of schedule. Already, advances in medical genetics have affected the day-to-day practice of medicine by providing more powerful approaches to diagnosis of genetic disorders and cancer. But the full impact of the integration of genetics into medical practice lies before us.

PTEN mutation spectrum and genotype-phenotype correlations in Bannayan-Riley-Ruvalcaba syndrome suggest a single entity with Cowden syndrome

Germline mutations in the tumour suppressor gene PTEN have been implicated in two hamartoma syndromes that exhibit some clinical overlap, Cowden syndrome (CS) and Bannayan-Riley-Ruvalcaba syndrome (BRR). PTEN maps to 10q23 and encodes a dual specificity phosphatase, a substrate of which is phosphatidylinositol 3,4,5-triphosphate, a phospholipid in the phosphatidylinositol 3-kinase pathway. CS is characterized by multiple hamartomas and an increased risk of benign and malignant disease of the breast, thyroid and central nervous system, whilst the presence of cancer has not been formally documented in BRR. The partial clinical overlap in these two syndromes is exemplified by the hallmark features of BRR: macrocephaly and multiple lipomas, the latter of which occur in a minority of individuals with CS. Additional features observed in BRR, which may also occur in a minority of CS patients, include Hashimoto's thyroiditis, vascular malformations and mental retardation. Pigmented macules of the glans penis, delayed motor development and neonatal or infant onset are noted only in BRR. In this study, constitutive DNA samples from 43 BRR individuals comprising 16 sporadic and 27 familial cases, 11 of which were families with both CS and BRR, were screened for PTEN mutations. Mutations were identified in 26 of 43 (60%) BRR cases. Genotype-phenotype analyses within the BRR group suggested a number of correlations, including the association of PTEN mutation and cancer or breast fibroadenoma in any given CS, BRR or BRR/CS overlap family ( P = 0.014), and, in particular, truncating mutations were associated with the presence of cancer and breast fibroadenoma in a given family ( P = 0.024). Additionally, the presence of lipomas was correlated with the presence of PTEN mutation in BRR patients ( P = 0.028). In contrast to a prior report, no significant difference in mutation status was found in familial versus sporadic cases of BRR ( P = 0.113). Comparisons between BRR and a previously studied group of 37 CS families suggested an increased likelihood of identifying a germline PTEN mutation in families with either CS alone or both CS and BRR when compared with BRR alone ( P = 0.002). Among CS, BRR and BRR/CS overlap families that are PTEN mutation positive, the mutation spectra appear similar. Thus, PTEN mutation-positive CS and BRR may be different presentations of a single syndrome and, hence, both should receive equal attention with respect to cancer surveillance.

Genetic testing for patients with renal disease: procedures, pitfalls, and ethical considerations

The Human Genome Project is rapidly producing insights into the molecular basis of human genetic disorders. The most immediate clinical benefit is the advent of new diagnostic methods. Molecular diagnostic tools are available for several genetic renal disorders and are in development for many more. Two general approaches to molecular diagnosis are linkage-based testing and direct mutation detection. The former is used when the gene has not been cloned but has been mapped in relation to polymorphic loci. Linkage-based testing is also helpful when a large diversity of mutations makes direct detection difficult. Limitations include the need to study multiple family members, the need for informative polymorphisms, and genetic heterogeneity. Direct mutation detection is limited by genetic heterogeneity and the need to distinguish nonpathogenic allelic variants from pathogenic mutations. Molecular testing raises a number of complex ethical issues, including those associated with prenatal or presymptomatic diagnosis. In addition, there are concerns about informed consent, privacy, genetic discrimination, and technology transfer for newly developed tests. Health professionals need to be aware of the technical and ethical implications of these new methods of testing, as well as the complexities in test interpretation, as molecular approaches are increasingly integrated into medical practice.

Descriptive analysis of tibial pseudarthrosis in patients with neurofibromatosis 1

Five percent of individuals with neurofibromatosis type 1 (NF1) present with congenital long bone pseudarthrosis (PA). In large series, 50-80% of patients with congenital long bone PA also have NF1. Very little information exists on the natural history and pathogenesis of PA in NF1. This report is a descriptive analysis of a large series of patients with NF1 and tibial bowing or PA. Study A is a case-control study using the National Neurofibromatosis Foundation International Database (NNFFID). Eighty-five patients with PA were compared to a control group from the same database. There was a statistically significant male predominance of NF1 cases with PA (54 males to 31 females), compared to controls (85 males to 87 females) (chi2 = 4.0, P = 0.046, using a two-tailed test with Yates' correction). There was no significant difference in the clinical presentation of NF1 manifestations in NF1 patients with PA than in NF1 patients without PA. Of the affected individuals with PA, there were 24 de novo cases and 21 familial cases (9 through maternal and 12 through paternal inheritance). Questions that could not be answered by Study A were addressed by a partially overlapping case-series report, Study B, in which data on 75 cases ascertained through questionnaires completed by NF center directors were collected. From Study B we determined that half of the patients who had a fracture sustained it before age 2, and approximately 16% of the pseudarthrosis patients had an amputation. Our data indicate a male predominance and no parent-of-origin effect. Male gender may be a susceptibility factor for pseudarthrosis in NF1.

Structural anomalies revealed by neuroimaging studies in the brains of patients with neurofibromatosis type 1 and large deletions

PURPOSE

The basis for cognitive problems in patients with neurofibromatosis type 1 (NF1) is unknown. A subset of NF1 patients with deletion of the entire NF1 gene has severe learning problems or mental retardation. We have reviewed neuroimaging studies (CT and MRI) in five such patients to determine whether structural anomalies in the brain are present and might explain the impaired cognitive function.

METHODS

Five patients with NF1 and deletion of the entire gene were identified by FISH studies. A retrospective review was conducted of CT and MRI images, as well as of data from developmental assessments.

RESULTS

All five patients had severe developmental impairment. None had been exposed to chemotherapy or radiation therapy. All had multiple regions of bright T2 signal intensity. Structural anomalies were seen in three of the five patients and included callosal dysgenesis in one, septum cavum vergae and pellucidum in two, mega cisterna magna in one, and Chiari I malformation with severe hydrocephalus in one patient.

CONCLUSION

Individuals with NF1 and large gene deletions have an increased frequency of structural anomalies of the brain not usually seen in NF1 patients. This suggests that the mental retardation in these individuals is due, at least in part, to abnormal brain development rather than a defect in brain function due to haplosufficiency of the NF1 gene product.

Plexiform neurofibromas

Plexiform neurofibromas are among the most common and debilitating complications of neurofibromatosis type 1 (NF1). They account for substantial morbidity, including disfigurement, functional impairment, and may even be life threatening. Plexiform neurofibromas are also subject to transformation into malignant peripheral nerve sheath tumor (MPNST), a complication that is refractory to treatment both because of a paucity of effective therapies for malignant soft tissue sarcomas in general, and because of the delay in diagnosis that results from change of a small portion of a large pre-existing tumor. The current mainstay of treatment of plexiform neurofibromas, and of MPNST for that matter, is surgical resection. The major variables are the timing and means of identification of plexiform neurofibromas, methods of follow-up, and indications for surgery. There is no established means of medical treatment, but research into the molecular pathogenesis of NF1, as well as advances in tumor therapy in general, are opening the way towards clinical trials for plexiform neurofibroma. Am. J. Med. Genet. (Semin. Med. Genet.) 89:31-37, 1999.

Genetic heterogeneity of Saethre-Chotzen syndrome, due to TWIST and FGFR mutations

Thirty-two unrelated patients with features of Saethre-Chotzen syndrome, a common autosomal dominant condition of craniosynostosis and limb anomalies, were screened for mutations in TWIST, FGFR2, and FGFR3. Nine novel and three recurrent TWIST mutations were found in 12 families. Seven families were found to have the FGFR3 P250R mutation, and one individual was found to have an FGFR2 VV269-270 deletion. To date, our detection rate for TWIST or FGFR mutations is 68% in our Saethre-Chotzen syndrome patients, including our five patients elsewhere reported with TWIST mutations. More than 35 different TWIST mutations are now known in the literature. The most common phenotypic features, present in more than a third of our patients with TWIST mutations, are coronal synostosis, brachycephaly, low frontal hairline, facial asymmetry, ptosis, hypertelorism, broad great toes, and clinodactyly. Significant intra- and interfamilial phenotypic variability is present for either TWIST mutations or FGFR mutations. The overlap in clinical features and the presence, in the same genes, of mutations for more than one craniosynostotic condition-such as Saethre-Chotzen, Crouzon, and Pfeiffer syndromes-support the hypothesis that TWIST and FGFRs are components of the same molecular pathway involved in the modulation of craniofacial and limb development in humans.

Complex familial rearrangement of chromosome 9p24.3 detected by FISH

We describe a newborn male with minor facial anomalies, pyloric stenosis, and a chromosome rearrangement that involves deletion and addition of material at 9p24.3. Routine studies showed a 46, XY, add (9) (p24) karyotype. Fluorescence in situ hybridization (FISH) with two different whole chromosome probes for chromosome 9 failed to identify whether the additional material was derived from that chromosome. FISH with single copy YAC probes from 9p24 (D9S1858, D9S1813 and D9S54) showed a more complex rearrangement involving a deletion at D9S1858 but not at D9S1813 or D9S54. Parental chromosome studies demonstrated an apparently identical 9p abnormality in the patient's mother. This report describes a familial chromosome rearrangement in an abnormal child and his normal mother and demonstrates the use and limitations of FISH in characterizing chromosomal abnormalities.

Neurocutaneous syndromes: neurofibromatosis 1, neurofibromatosis 2, and tuberous sclerosis

Neurofibromatosis 1, neurofibromatosis 2, and tuberous sclerosis are a set of dominantly transmitted disorders that have in common the tendency towards formation of tumors of the nervous system and other tissues. The genes for neurofibromatosis 1, neurofibromatosis 2, and one of two forms of tuberous sclerosis have been identified and appear to act as tumor suppressor genes. Information is accumulating about pathogenesis that may eventually improve our ability to diagnose and treat these disorders.

Deletion of the entire NF1 gene causing distinct manifestations in a family

We identified a father and son with neurofibromatosis type 1 (NF1) due to a deletion of the entire NF1 gene detected by fluorescence in situ hybridization (FISH). As is the case for others reported to have such large deletions, father and son had severe NF1, including a large number of cutaneous neurofibromas, facial anomalies, large hands, feet, and head, and developmental impairment. They were discordant in that seizures and plexiform neurofibromas occurred only in the propositus. Large NF1 deletions can be compatible with familial transmission and appear to be associated with a distinct phenotype.

Somatic mosaicism for deletion of the entire NF1 gene identified by FISH

We report a young child with a large congenital cervical plexiform neurofibroma and multiple café-aul-ait spots in a generalized distribution who has mosaicism for complete deletion of the NF1 gene. The deletion was demonstrated with intragenic cosmid probes as well as YACs spanning a 700-kb contig including NF1, by two-color FISH with an NF1 and a control probe. Using different intragenic probes, deletion was found in 77-84% of cultured peripheral blood lymphocytes but not in cultured skin fibroblasts. Neither parent has signs of neurofibromatosis type 1 (NF1) or a gene deletion. This is the first report of mosaicism for complete deletion of the NF1 gene. The child did not have typical NF1 or display segmental features of NF1.

Ophthalmological issues in the neurofibromatoses

The neurofibromatoses are a set of at least two distinct disorders characterized by the development of nerve sheath tumors and diverse other features. Both are genetically determined as autosomal dominant traits, and both genes have been identified, with resultant major insights into pathogenesis. The neurofibromatoses have prominent effects on the visual system, which are important both for diagnosis and clinical management. This review focuses on clinical aspects of the neurofibromatoses, highlighting ophthalmological issues and recent advances in molecular genetics.

Neurobehavioral profiles of children with neurofibromatosis 1 referred for learning disabilities are sex-specific

We compared neurobehavioral profiles of 10 children with neurofibromatosis 1 (NF-1) referred for evaluation of learning disabilities (NF/LD) to those to learning disabled children without known genetic disease (LD), matched for age, sex, and estimated IQ. It was hypothesized that the NF/LD children would exhibit a neurobehavioral profile diagnostic of compromise of frontal/subcortical brain systems while those of the case controls would be heterogeneous. Records from a clinical data base were reviewed retrospectively for the neurological and neuropsychological components of an interdisciplinary learning disabilities evaluation. Neurological abnormalities were more frequent in the NF/LD group, involving gross and fine motor coordination, praxis, and megencephaly. As predicted, clinical neuropsychological diagnostic ratings and composite neurobehavioral observation scores were consistent with compromise of frontal systems in the NF/LD group. An unanticipated finding was that outcomes in the NF/LD group were sex dependent: Megencephaly was observed in females only; and the frontal/subcortical neurobehavioral profile was more consistently observed in females. Females with NF-1 with megencephaly may be at increased risk for a neurobehavioral syndrome contributing to LD that is consistent with compromise of frontal/subcortical brain systems.

Advances in molecular diagnosis

Approaches to the diagnosis of genetic disease using the tools of molecular genetics are being developed at a rapid pace as efforts to map the human genome progress. Technical challenges remain, however, in devising approaches to permit the wide diversity of pathogenic mutations to be identified in an efficient manner. Moreover, the possibility of population screening for carrier status for gene mutations raises important ethical and social questions. Major progress has been made in both areas and the list of disorders amenable to molecular diagnosis is expanding rapidly.

Distal 8p deletion (8)(p23.1): an easily missed chromosomal abnormality that may be associated with congenital heart defect and mental retardation

We describe the clinical manifestations and molecular cytogenetic analyses of three patients with a similar distal deletion of chromosome 8. Each child had mild developmental delay and subtle minor anomalies. Two had cardiac anomalies but no other major congenital anomalies were present. High resolution G and R banding showed in all three patients del(8)(p23.1), but the breakpoint in case 1 was distal to 8p23.1, in case 2 was in the middle of 8p23.1, and in case 3 proximal to 8p23.1. Fluorescence in situ hybridization (FISH) studies with a chromosome 8 paint probe confirmed that no other rearrangement had occurred. FISH with a chromosome 8-specific telomere probe indicated that two patients had terminal deletions. Chromosome analysis of the parents of case 1 and mother of case 2 were normal; the remaining parents were not available for study. Thirteen individual patients including the three in this study, and three relatives in one family with del(8)(p23.1), have been reported in the past 5 years. Major congenital anomalies, especially congenital heart defects, are most often associated with a breakpoint proximal to 8p23.1. Three patients were found within a 3-year period in this study and five cases were found within 4 years by another group, indicating that distal 8p deletion might be a relatively common chromosomal abnormality. This small deletion is easily overlooked (i.e., cases 1 and 2 were reported as normal at amniocentesis) and can be associated with few or no major congenital anomalies.

Pitfalls in the interpretation of molecular diagnostic tests

Application of the tools of molecular genetics has vastly increased the power of genetic diagnosis, but also raises significant challenges in interpretation. Molecular tests can be used for diagnosis of an affected individual or determination of carrier status. Either direct mutation analysis or linkage analysis is used in various disorders. Major pitfalls in interpretation of direct tests include mistaking polymorphisms for mutations, inaccurate prognostication based on identification of a mutation, and misinterpretation of the implications of not finding a mutation. Interpretation of linkage tests must take account of the accuracy of proband diagnosis, interpretation of family relationships, and genetic recombination. Cognizance of these issues is vital to avoidance of clinical errors and must be incorporated into genetic counseling.

ARMS test for diagnosis of factor VLeiden mutation, a common cause of inherited thrombotic tendency

We developed a simple and rapid amplification-refractory mutation system (ARMS) assay for the factor V mutation [R506Q] (factor VLeiden), which results in the autosomal dominant thrombotic tendency, resistance to activated protein C (rAPC). PCR primers within Exon 10 of the factor V gene were designed. A common upstream primer was paired with either a mutant or wild-type-specific downstream primer. The 3'-most nucleotide of the specific primers recognized either the mutant or normal allele, and the 3' penultimate nucleotide was mismatched to enhance specificity of the reaction. The assay was validated using authentic factor VLeiden DNA samples. Seven of 103 hematologically normal children (6.8%) were found to be heterozygotes. Among 27 patients studied by the rAPC assay, ARMS assay and rAPC results were concordant in 26. Among these were a 1-year-old child with a calcified clot in the inferior vena cava. Both the patient and his father were heterozygous for the mutation and both had abnormal rAPC assays. rAPC and factor VLeiden assays were discordant in a young girl with a history of stroke. Biochemical rAPC assay was abnormal, while ARMS assay revealed amplification only with wild-type primers, suggesting a non-[R506Q] mechanism for rAPC. This assay will be a valuable tool for studying subjects with thromboses and their family members.

Deletion of the entire NF1 gene detected by the FISH: four deletion patients associated with severe manifestations

Genetic analysis of NF1 has indicated a wide diversity of mutations, including chromosome rearrangements, deletions, insertions, duplications, and point mutations. Recently, five severely affected individuals have been found by Kayes et Al. [1994] to have deletions encompassing the entire gene. These deletions were detected by quantitative Southern analysis. To simplify deletion detection, we have employed fluorescence in situ hybridization (FISH) using intragenic probes. Thirteen unrelated individuals with NF1 have been studied. Among six with severe manifestations, four have been found to have deletions detected by probes cFF13, cFB5D, cP5, yA43A9, yA113D7 and yD8F4. All four deletions patients have severe developmental delay, minor and major anomalies (including one with bilateral iris colobomas), and multiple cutaneous neurofibromas or plexiform neurofibromas which were present before age 5 years. FISH provides a simple and rapid means of identification of NF1 gene deletions and will allow more rigorous testing of the hypothesis that such deletions are associated with severe manifestations.

17q inversion involving the neurofibromatosis type one locus in a family with neurofibromatosis type one

We report a family with a paracentric inversion of the long arm of chromosome 17 [inv(17)(q11.2q25.1)] and neurofibromatosis type one (NF1). The family was ascertained because of NF1 and multiple miscarriages. Fluorescence in situ hybridization using cosmid probes from opposite ends of the NF1 gene confirmed that the inversion disrupts the gene. Using field inversion gel electrophoresis we have found that the inversion separates cDNA probes FB5D and AE25, which are normally adjacent to one another in the NF1 gene. This is the third published report of a gross chromosomal rearrangement responsible for NF1. The features in this family are typical for NF1, and are not unusually severe.

CHARGE association in a child with de novo inverted duplication (14)(q22-->q24.3)

We report on a 4-1/2 year old girl with apparent CHARGE association who had a de novo inverted duplication (14)(q22-->24.3), iris colobomas, ventricular septal defect, soft tissue choanal atresia, intellectual impairment, growth retardation, sensorineural deafness, apparently low set ears, and upslanting palpebral fissures. Family history was unremarkable and parental chromosomes were normal. Similarities between this and previously reported cases of 14q duplication suggest that a locus for a gene or genes causing some of the anomalies of CHARGE association may reside in the region 14q22 to 24.3.

Advances in genetic diagnosis

For many years, the mainstay of pediatric genetic testing was chromosomal analysis. Based on a technology developed in the 1950s and refined in the 1960s, this approach permitted the detection of abnormalities of chromosome number and some structural rearrangements. The past decade has seen an explosion in knowledge about the genetic basis of disease, and accompanying this, the development of new types of diagnostic tests. This article reviews some of these new approaches, and provides a practical guide for the pediatrician who is increasingly called upon to arrange for such testing and to interpret the results.

Patterns of seizures observed in association with neurofibromatosis 1

Clinical features of seizures occurring in a neurofibromatosis clinic population were examined in a retrospective study. Twenty-two individuals in a population of 359 persons with neurofibromatos 1 (NF1) had had one or more seizures. Age at first seizure ranged from 4 days to > 20 years. Patients were classified into five groups on the basis of medical history, seizure type, and EEG findings. Two patients had seizures in the first 3 months of life: 1 was born prematurely and had perinatal encephalopathy, and the other developed infantile spasms (IS) and had extensive growth of a plexiform neurofibroma. Two males had seizures in association with aqueductal stenosis. Six individuals had one or more generalized seizures with fever, and 3 had primary generalized epilepsy. Nine patients had complex partial seizures (CPS), which varied in clinical manifestations and response to antiepileptic drugs (AEDs). In none of the individuals with seizures in this study was a structural lesion in the brain visible by neuroimaging. Seizures appear to be relatively uncommon in individuals with NF1, and when they occur have a natural history similar to that of seizures in the general population.

Stage III neuroblastoma over 1 year of age at diagnosis: improved survival with intensive multimodality therapy including multiple alkylating agents

PURPOSE

A nonrandomized, single-arm trial was conducted to assess the efficacy of multimodality therapy including intensive chemotherapy with multiple alkylating agents in the treatment of children with Evans stage III neuroblastoma older than 1 year at diagnosis.

PATIENTS AND METHODS

Twenty-five patients with a median age of 18 months at diagnosis were treated with multimodality therapy including surgery and chemotherapy using either nitrogen mustard (mechlorethamine), doxorubicin, cisplatin, dacarbazine (DTIC), vincristine, and cyclophosphamide (MADDOC) or cisplatin and cyclophosphamide induction followed by maintenance MADDOC (induction MADDOC) protocols. Sixteen of 25 patients also received radiotherapy to the tumor bed and primary lymph nodes. Event-free survival (EFS) was compared with that reported previously in the literature. N-myc amplification was evaluated prospectively and the Shimada classification was evaluated retrospectively as potential prognostic factors.

RESULTS

We report a 72% EFS (95% confidence interval +/- 18%) with a median follow-up of 85 months. EFS was significantly worse for patients with tumors demonstrating N-myc amplification (P = .018). Patients classified as favorable according to the Shimada system experienced a significantly better EFS (P = .04), but unfavorable patients still maintained a 60% EFS.

CONCLUSION

Intensive multimodality treatment including MADDOC and induction MADDOC chemotherapy provides a very good EFS for children older than 1 year who have stage III neuroblastoma. Children classified as favorable according to the Shimada system have a better prognosis. Patients whose tumors demonstrate N-myc amplification have a poor prognosis despite therapy.

Diagnostic outcome in children with multiple café au lait spots

Forty-one children, ranging in age from 1 month to 14 years, had six or more café au lait spots at their initial visit and were examined annually. Signs of neurofibromatosis type 1 eventually developed in 24. The most common feature to appear to confirm the diagnosis was skin-fold freckling, which occurred in 18 subjects. Diagnosis was based on the appearance of Lisch nodules in 5, and on neurofibromas in 3. In most instances, diagnosis was established within 3 years of initial evaluation, usually before 5 years of age. Six children had a segmental distribution of café au lait spots, suggesting segmental neurofibromatosis. In 3, diagnoses other than neurofibromatosis type 1 were established (Bannayan-Riley-Rulvalcaba syndrome, multiple lentigines syndrome, and fibrous dysplasia). In 8 subjects only multiple café au lait spots are present, and no definite diagnosis has been established. It is concluded that with regular follow-up, including physical and ophthalmological examinations, a definite diagnosis, most commonly neurofibromatosis type 1, can be established for most children having multiple café au lait spots.

Locomotor problems in infantile facioscapulohumeral muscular dystrophy. Retrospective study of 9 patients

A retrospective study of 9 patients with infantile facioscapulohumeral muscular dystrophy defines orthopedic deformities and progression. Patients presented in the early months of life with facial diplegia. Sensorineural hearing loss occurred in 8 out of 9 with a mean onset at 5 (2-9) years. Walking began at the normal time, but worsened progressively, which was due mainly to gluteus maximus muscle weakness. Scapular winging, extreme lumbar lordosis, and foot drop were characteristic. The majority of patients (in this and other series) lose walking ability in the second decade. Efforts to control lumbar lordosis by bracing while the patients were still walking were ineffective. Control of lumbar lordosis after the patients are wheelchair-dependent is important.

Galactose metabolism and reproductive history in women with type 1 neurofibromatosis

To explore a possible relationship between neurofibromatosis and abnormalities of galactose metabolism, we examined the activity and characteristics of red cell galactokinase and galactose-1-phosphate uridyl transferase in 14 white women with type 1 neurofibromatosis and in 28 control women. Women with NF1 had a significantly lower activity of galactokinase and were more likely to have the 3-band pattern on electrophoresis of their transferase enzyme known as the Duarte variant. In addition, we found that women with NF1 were more likely to have reproductive histories suggestive of hypogonadism, including irregular menses, infertility, ovarian cysts, and early menopause. We conclude that abnormalities of galactose metabolism may be linked to abnormalities of both germ cell and neural crest development.

Characterization of N-myc amplification in a human neuroblastoma cell line by clones isolated following the phenol emulsion reassociation technique and by hexagonal field gel electrophoresis

The N-myc amplification of human neuroblastomas was characterized by the amplified DNA cloned from the cell line MC-NB-1 using the phenol emulsion reassociation technique (PERT). A number of PERT clones exhibiting amplification in this cell line were tested for amplification in other neuroblastoma cell lines. In almost all cell lines examined, only a few clones were co-amplified with N-myc and most of the others were exclusively amplified in a subset of the cell lines. The total aggregate size of the Hind III fragment identified by the PERT clones was approximately 350 kb. Most of the PERT clones were mapped to human chromosome (chr) 2p23-2pter, where the N-myc gene is located. Four types of amplicons, the 100, 420, 480 and 520 kb fragments, shown to be Not I fragments, were identified by hexagonal field gel electrophoresis. Three fragments are ordered in a head-to-tail array, and the remaining fragment is either ordered in a tail-to-head array or something else. Despite the extremely unusual construction of the amplified sequences in this cell line as compared with others, there was a low degree of sequence heterogeneity among the amplicons within this cell line. These observations lead to the idea that the complex rearrangements that give rise to the heterogeneous organization of the amplified sequences among the different cell lines precede the amplification of these sequences.

myc gene amplification and expression in primary human neuroblastoma

Although N-myc amplification in neuroblastomas correlates with poor prognosis, not all neuroblastomas which fail to respond to therapy have N-myc amplification. To determine whether other modes of myc gene activation underlie progression of some neuroblastomas, 45 were analyzed for amplification of N-myc, c-myc and L-myc and 26 were studied for transcription of these oncogenes. N-myc amplification was found in 6 of 45 tumors; no tumor had amplification of c-myc or L-myc. Transcription of both N-myc and c-myc occurred in 21 of 26 neuroblastomas. No tumor without N-myc amplification had a level of N-myc expression near that of a tumor or cell line with amplification. One tumor with N-myc amplification was the only specimen with N-myc but not c-myc expression. Five samples had c-myc but not N-myc expression; all had histological features of ganglioneuroma. DNA index did not correlate with myc gene amplification or expression. It is concluded that N-myc and c-myc are commonly expressed in primary untreated neuroblastomas, but in the absence of N-myc amplification, expression of these genes does not appear to correlate with disease progression.

Flanking markers for the gene causing von Recklinghausen neurofibromatosis (NF1)

The defective gene causing von Recklinghausen neurofibromatosis (NF1), one of the most common inherited disorders affecting the human nervous system, was recently mapped to chromosome 17. We have used additional DNA markers to further narrow and bracket the NF1 defect. A multipoint linkage analysis suggests that the NF1 gene is flanked by D17Z1 on the centromeric side and by EW 207 on the telomeric side of the long arm of chromosome 17. The identification of closely linked flanking markers should allow us to develop a reliable prenatal and presymptomatic diagnostic test for this serious neurological disorder and provides the basis for applying chromosome-specific cloning techniques for the isolation and characterization of the mutant gene.

The neurofibromatoses. What do we know about them?

These are exciting times for patients and physicians concerned with the neurofibromatoses. These disorders have been known to medicine for more than 100 years, and now there is hope of achieving a thorough understanding of their pathogenesis. Despite this optimism, the need for careful clinical management of these patients and for solid clinical research to better define the natural history of the disorders will remain for some time. Success of the research depends in large part on studying patients with carefully documented diagnoses, and long after the genes for the neurofibromatoses are identified, work will go on to apply the new knowledge to the benefit of those affected with the disorders.

Linkage analysis in von Recklinghausen neurofibromatosis (NF1) with DNA markers for chromosome 17

The mutant gene causing von Recklinghausen neurofibromatosis (NF1) was recently shown to map to chromosome 17. We have used additional markers for chromosome 17 to narrow further the location of the gene defect. A preliminary multipoint linkage analysis suggests that the NF1 gene is located on the long arm of chroomsome 17, flanked by D17Z1 and NGFR. Linkage analysis with the human oncogene homolog erbA1, which maps to this region, suggests that this cancer-related gene is not the primary cause of NF1.