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BackgroundGermline variants inPTPN11are the primary cause of Noonan syndrome with multiple lentigines (NSML) and Noonan syndrome (NS), which share common skin and facial symptoms, cardiac anomalies and retardation of growth. Hearing loss is considered an infrequent feature in patients with NSML/NS. However, in our cohort, we identified a group of patients withPTPN11pathogenic variants that were primarily manifested in congenital sensorineural hearing loss (SNHL). This study evaluated the incidence ofPTPN11-related NSML or NS in patients with congenital SNHL and explored the expression ofPTPN11and the underlying mechanisms in the auditory system.MethodsA total of 1502 patients with congenital SNHL were enrolled. Detailed phenotype-genotype correlations were analysed in patients withPTPN11variants. Immunolabelling of Ptpn11 was performed in P35 mice. Zebrafish withPtpn11knockdown/mutant overexpression were constructed to further explore mechanism underlying the phenotypes.ResultsTen NSML/NS probands were diagnosed via the identification of pathogenic variants ofPTPN11, which accounted for ~0.67% of the congenital SNHL cases. In mice cochlea, Shp2, which is encoded byPtpn11, is distributed in the spiral ganglion neurons, hair cells and supporting cells of the inner ear. In zebrafish, knockdown ofptpn11aand overexpression of mutantPTPN11were associated with a significant decrease in hair cells and supporting cells. We concluded that congenital SNHL could be a major symptom inPTPN11-associated NSML or NS. Other features may be mild, especially in children.ConclusionScreening forPTPN11in patients with congenital hearing loss and variant-based diagnoses are recommended.

BackgroundThis study evaluates 6 years of prenatal rasopathy testing in the Netherlands, updates on previous data and gives recommendations for prenatal rasopathy testing.Methods424 fetal samples, sent in for prenatal rasopathy testing in 2011–2016, were collected. Cohort 1 included 231 samples that were sequenced for 1–5 rasopathy genes. Cohort 2 included 193 samples that were analysed with a 14-gene next generation sequencing (NGS) panel. For all mutation-positive samples in both cohorts, the referring physician provided detailed ultrasound findings and postnatal follow-up. For 168 mutation-negative samples in cohort 2, solely clinical information on the requisition form was collected.ResultsIn total, 40 (likely) pathogenic variants were detected (9.4%). All fetuses showed a variable degree of involvement of prenatal findings: increased nuchal translucency (NT)/cystic hygroma, distended jugular lymph sacs (JLS), hydrops fetalis, polyhydramnios, pleural effusion, ascites, cardiac defects and renal anomalies. An increased NT was the most common finding. Eight fetuses showed solely an increased NT/cystic hygroma, which were all larger than 5.5 mm. Ascites and renal anomalies appeared to be poor predictors of pathogenic outcome.ConclusionFetuses with a rasopathy show in general multiple ultrasound findings. The larger the NT and the longer it persists, the more likely it is to find a pathogenic variant. Rasopathy testing is recommended when the fetus shows an isolated increased NT ≥5.0 mm or when NT of ≥3.5 mm and at least one of the following ultrasound anomalies is present: distended JLS, hydrops fetalis, polyhydramnios, pleural effusion, ascites, cardiac defects and renal anomalies.

Germline variants inA total of 1502 patients with congenital SNHL were enrolled. Detailed phenotype-genotype correlations were analysed in patients withTen NSML/NS probands were diagnosed via the identification of pathogenic variants ofScreening for

Background Noonan syndrome with multiple lentigines (NSML), formerly known as LEOPARD syndrome, is an autosomal-dominant disorder characterised by lentigines, EKG abnormalities, ocular hypertelorism, pulmonic stenosis, abnormal genitalia, growth retardation and deafness. There is significant clinical overlap between NSML and other disorders that result from dysregulated rat sarcoma/mitogen-activated protein kinase pathway (RASopathies). Except for neurofibromatosis type 1, other RASopathies are not known to be typically associated with neurogenic tumours. Methods and results We evaluated patients from three families with pigmentary skin lesions, progressive neuropathy, enlarged nerves, massive burden of paraspinal tumours (neurofibroma was confirmed in one patient) and a clinical diagnosis of NSML. All patients had a mutation in the protein tyrosine phosphatase catalytic domain of the PTPN11 gene; two unrelated patients had the p.Thr468Met mutation, while the family consisting of two affected individuals harboured the p.Thr279Cys mutation. Molecular analysis performed on hypertrophic nerve tissue did not disclose a second somatic hit in NF1, PTPN11, NF2 or SMARCB1 genes. Conclusions Neurogenic tumours and hypertrophic neuropathy are unusual complications of NSML and may be an under-recognised manifestation that would warrant surveillance. Our observation may also have implications for other disorders caused by RAS-pathway dysregulation.

Background Infants with Noonan syndrome (NS) are predisposed to developing juvenile myelomonocytic leukaemia (JMML) or JMML-like myeloproliferative disorders (MPD). Whereas sporadic JMML is known to be aggressive, JMML occurring in patients with NS is often considered as benign and transitory. However, little information is available regarding the occurrence and characteristics of JMML in NS. Methods and results Within a large prospective cohort of 641 patients with a germline PTPN11 mutation, we identified MPD features in 36 (5.6%) patients, including 20 patients (3%) who fully met the consensus diagnostic criteria for JMML. Sixty percent of the latter (12/20) had severe neonatal manifestations, and 10/20 died in the first month of life. Almost all (11/12) patients with severe neonatal JMML were males. Two females who survived MPD/JMML subsequently developed another malignancy during childhood. Although the risk of developing MPD/JMML could not be fully predicted by the underlying PTPN11 mutation, some germline PTPN11 mutations were preferentially associated with myeloproliferation: 10/48 patients with NS (20.8%) with a mutation in codon Asp61 developed MPD/JMML in infancy. Patients with a p.Thr73Ile mutation also had more chances of developing MPD/JMML but with a milder clinical course. SNP array and whole exome sequencing in paired tumoral and constitutional samples identified no second acquired somatic mutation to explain the occurrence of myeloproliferation. Conclusions JMML represents the first cause of death in PTPN11 -associated NS. Few patients have been reported so far, suggesting that JMML may sometimes be overlooked due to early death, comorbidities or lack of confirmatory tests.

Background Mutations in Ras/mitogen-activated protein kinase (Ras/MAPK) pathway genes lead to a class of disorders known as RASopathies, including neurofibromatosis type 1 (NF1), Noonan syndrome (NS), Costello syndrome (CS), and cardio-facio-cutaneous syndrome (CFC). Previous work has suggested potential genetic and phenotypic overlap between dysregulation of Ras/MAPK signalling and autism spectrum disorders (ASD). Although the literature offers conflicting evidence for association of NF1 and autism, there has been no systematic evaluation of autism traits in the RASopathies as a class to support a role for germline Ras/MAPK activation in ASDs. Methods We examined the association of autism traits with NF1, NS, CS and CFC, comparing affected probands with unaffected sibling controls and subjects with idiopathic ASDs using the qualitative Social Communication Questionnaire (SCQ) and the quantitative Social Responsiveness Scale (SRS). Results Each of the four major RASopathies showed evidence for increased qualitative and quantitative autism traits compared with sibling controls. Further, each RASopathy exhibited a distinct distribution of quantitative social impairment. Levels of social responsiveness show some evidence of correlation between sibling pairs, and autism-like impairment showed a male bias similar to idiopathic ASDs. Conclusions Higher prevalence and severity of autism traits in RASopathies compared to unaffected siblings suggests that dysregulation of Ras/MAPK signalling during development may be implicated in ASD risk. Evidence for sex bias and potential sibling correlation suggests that autism traits in the RASopathies share characteristics with autism traits in the general population and clinical ASD population and can shed light on idiopathic ASDs.

Cardio‐facio‐cutaneous (CFC) syndrome, Noonan syndrome (NS), and Costello syndrome (CS) are clinically related developmental disorders that have been recently linked to mutations in the RAS/MEK/ERK signalling pathway. This study was a mutation analysis of the KRAS, BRAF, MEK1 and MEK2 genes in a total of 130 patients (40 patients with a clinical diagnosis of CFC, 20 patients without HRAS mutations from the French Costello family support group, and 70 patients with NS without PTPN11 or SOS1 mutations). BRAF mutations were found in 14/40 (35%) patients with CFC and 8/20 (40%) HRAS‐negative patients with CS. KRAS mutations were found in 1/40 (2.5%) patients with CFC, 2/20 (10%) HRAS‐negative patients with CS and 4/70 patients with NS (5.7%). MEK1 mutations were found in 4/40 patients with CFC (10%), 4/20 (20%) HRAS‐negative patients with CS and 3/70 (4.3%) patients with NS, and MEK2 mutations in 4/40 (10%) patients with CFC. Analysis of the major phenotypic features suggests significant clinical overlap between CS and CFC. The phenotype associated with MEK mutations seems less severe, and is compatible with normal mental development. Features considered distinctive for CS were also found to be associated with BRAF or MEK mutations. Because of its particular cancer risk, the term “Costello syndrome” should only be used for patients with proven HRAS mutation. These results confirm that KRAS is a minor contributor to NS and show that MEK is involved in some cases of NS, demonstrating a phenotypic continuum between the clinical entities. Although some associated features appear to be characteristic of a specific gene, no simple rule exists to distinguish NS from CFC easily.

Background: Rare reports on patients with congenital myopathy with excess of muscle spindles (CMEMS), hypertrophic cardiomyopathy, and variable features resembling Noonan syndrome have been published, but the genetic basis of this condition has been unknown. Methods and Results: We analyzed PTPN11 and RAS genes in five unrelated patients with this phenotype and found HRAS mutations in four of them. Two disease-associated mutations, G12V and G12S, have previously been observed in patients with Costello syndrome (CS), while two other mutations, E63K and Q22K, are novel. All four mutations are predicted to enhance downstream H-Ras signaling, suggesting that CMEMS is a developmental consequence of sustained H-Ras activation in skeletal muscle. Conclusion: This type of myopathy may represent a previously unrecognized manifestation of CS. However, some patients carrying HRAS mutations may exhibit prominent congenital muscular dysfunction, while features of CS are less obvious, suggesting that germline HRAS mutations may underlie some cases of otherwise unclassified neonatal neuromuscular disorders.

Background Noonan syndrome is an autosomal dominant, multisystemic disorder caused by dysregulation of the RAS/mitogen activated protein kinase (MAPK) pathway. Heterozygous, pathogenic variants in 11 known genes account for approximately 80% of cases. The identification of novel genes associated with Noonan syndrome has become increasingly challenging, since they might be responsible for very small fractions of the cases. Methods A cohort of 50 Brazilian probands negative for pathogenic variants in the known genes associated with Noonan syndrome was tested through whole-exome sequencing along with the relatives in the familial cases. Families from the USA and Poland with mutations in the newly identified genes were included subsequently. Results We identified rare, segregating or de novo missense variants in SOS2 and LZTR1 in 4% and 8%, respectively, of the 50 Brazilian probands. SOS2 and LZTR1 variants were also found to segregate in one American and one Polish family. Notably, SOS2 variants were identified in patients with marked ectodermal involvement, similar to patients with SOS1 mutations. Conclusions We identified two novel genes, SOS2 and LZTR1 , associated with Noonan syndrome, thereby expanding the molecular spectrum of RASopathies. Mutations in these genes are responsible for approximately 3% of all patients with Noonan syndrome. While SOS2 is a natural candidate, because of its homology with SOS1 , the functional role of LZTR1 in the RAS/MAPK pathway is not known, and it could not have been identified without the large pedigrees. Additional functional studies are needed to elucidate the role of LZTR1 in RAS/MAPK signalling and in the pathogenesis of Noonan syndrome.

Background: Noonan syndrome, cardio-facio-cutaneous syndrome (CFC) and Costello syndrome constitute a group of developmental disorders with an overlapping pattern of congenital anomalies. Each of these conditions can be caused by germline mutations in key components of the highly conserved Ras-MAPK pathway, possibly reflecting a similar pathogenesis underlying the three disorders. Germline mutations in KRAS have recently been identified in a small number of patients with Noonan syndrome and CFC. Methods and results: 260 patients were screened for KRAS mutations by direct sequencing. Overall, we detected KRAS mutations in 12 patients, including three known and eight novel sequence alterations. All mutations are predicted to cause single amino acid substitutions. Remarkably, our cohort of individuals with KRAS mutations showed a high clinical variability, ranging from Noonan syndrome to CFC, and also included two patients who met the clinical criteria of Costello syndrome. Conclusion: Our findings reinforce the picture of a clustered distribution of disease associated KRAS germline alterations. We further defined the phenotypic spectrum associated with KRAS missense mutations and provided the first evidence of clinical differences in patients with KRAS mutations compared with Noonan syndrome affected individuals with heterozygous PTPN11 mutations and CFC patients carrying a BRAF , MEK1 or MEK1 alteration, respectively. We speculate that the observed phenotypic variability may be related, at least in part, to specific genotypes and possibly reflects the central role of K-Ras in a number of different signalling pathways.

Background: Costello syndrome (CS) is a rare multiple congenital abnormality syndrome, associated with failure to thrive and developmental delay. One of the more distinctive features in childhood is the development of facial warts, often nasolabial and in other moist body surfaces. Individuals with CS have an increased risk of malignancy, suggested to be about 17%. Recently, mutations in the HRAS gene on chromosome 11p13.3 have been found to cause CS. Methods: We report here the results of HRAS analysis in 43 individuals with a clinical diagnosis of CS. Results: Mutations were found in 37 (86%) of patients. Analysis of parental DNA samples was possible in 16 cases for both parents and in three cases for one parent, and confirmed the mutations as de novo in all of these cases. Three novel mutations (G12C, G12E, and K117R) were found in five cases. Conclusions: These results confirm that CS is caused, in most cases, by heterozygous missense mutations in the proto-oncogene HRAS. Analysis of the major phenotypic features by mutation suggests a potential correlation between malignancy risk and genotype, which is highest for patients with an uncommon (G12A) substitution. These results confirm that mutation testing for HRAS is a reliable diagnostic test for CS.

Editor—We present the clinical histories and physical findings in two unrelated, severely mentally retarded males, now 14 and 11 years old. Patient 1, a male, was born as the second and youngest child of healthy, unrelated Flemish parents with normal family histories. Pregnancy and delivery at 38 weeks' gestation were normal. Birth weight was 3200 g, length 47 cm, and head circumference 34 cm. Immediately after birth a number of dysmorphic signs were noted by the paediatrician, including facial oedema with ptosis of both eyelids, temporal flattening, hypertelorism, webbed neck, broad thorax with widely spaced, small, inverted nipples, shallow scrotum, and testes in the inguinal canal. The hands were broad and short with permanent oedema on the dorsum and the skin was loose and hyperextensible, especially on the arms. The diagnosis of Noonan syndrome was considered. Cardiac and renal echography was normal. Prometaphase chromosome studies on a peripheral blood lymphocyte culture showed a 46,XY normal male karyotype after G and R banding. Except for excessive weight loss, down to 2600 g, no major problems were noted in the neonatal period. In the first two years of life mild psychomotor retardation was noted with discrete hypertonia of the lower limbs. He started to walk without support on tiptoes at the age of 19 months. At the age of 2 years mental age was 15 months on the Bayley Developmental Scale. At the age of 3 years, the first episodes of epileptic attacks were noted with variable clinical presentation of the grand mal, petit mal, and myoclonic types. Seizures were resistant to anti-epileptic therapy and, from that age onwards, severe behavioural problems were noted with chaotic and destructive tantrums. …

The multiple lentigines syndrome is an autosomal dominant condition which has many similarities to Noonan syndrome, except in the most striking feature from which its name is derived. The less neutral but very apt mnemonic, LEOPARD syndrome, was first used by Gorlin et al to whom the major debt in the definition of this syndrome lies, that is, Lentigines, ECG abnormalities, Ocular hypertelorism/Obstructive cardiomyopathy, Pulmonary valve stenosis, Abnormalities of genitalia in males, Retardation of growth, and Deafness. Not previously included in the mnemonic is cardiomyopathy which is an important feature because it is associated with significant mortality.

The RASopathies constitute a diverse group of congenital disorders characterised by short stature, cardiac anomalies, distinctive facial features, predisposition to developing juvenile myelomonocytic leukaemia (JMML) and germline mutations in the Ras-mitogen activated protein kinase (MAPK) pathway.1 We recently described the genomic landscape of JMML, which can arise in the context of germline or somatic lesions in the Ras-MAPK pathway and identified somatic RRAS2 mutations as a novel lesion in JMML.2 We thus hypothesised that germline RRAS2 mutations could be an additional cause of Noonan syndrome (NS) and therefore screened 116 patients with NS who had no other identified lesions. No recurrent mutations were found in RRAS2 . Autosomal dominant germline mutations in a variety of Ras-MAPK pathway genes, including PTPN11, SOS1, KRAS, HRAS, MAP2K1, MAP2K2, NRAS, RAF1, CBL, NF1, SPRED1, BRAF, SHOC2, …

Editor—Noonan syndrome (NS) is an autosomal dominant developmental disorder in which the cardinal features include short stature, typical facies with hypertelorism, ptosis, downward slanting palpebral fissures, and low set, posteriorly rotated ears. In addition, there is a notable cardiac involvement seen in these patients, principally pulmonary valve stenosis and hypertrophic obstructive cardiomyopathy.1 2 The frequency of NS has been estimated to be between 1:1000-1:2500 live births.2 3 Using linkage analysis in a large three generation pedigree, we have previously mapped a gene for NS to an interval of more than 6 cM on 12q24 flanked by the markers D12S1637 and NOS1 .4 5 A similar analysis in smaller two generation families showed genetic heterogeneity for this disorder.4 Despite the relatively high incidence of NS, there appears to be a distinct lack of large families suitable for linkage analysis, possibly resulting from an increase of infertility in males.6 However, the location of the NS gene has recently been further refined to a 5 cM interval through the identification of additional recombinants in one additional large NS family.7 No chromosome rearrangements associated with the disease have so far been discovered. In view of this, one approach currently being used to identify the underlying gene responsible for this disorder is examination of candidate genes from within this large region of chromosome 12. We present below the examination of four candidate genes, the precise localisation of three of which, epidermal growth factor receptor pathway substrate-8 ( EPS8 ), decorin ( DCN ), and myosin light chain 2 ( MYL2 ), had not previously been accurately determined. The fourth, ribosomal protein L6 ( RPL6 ) was known to lie within the NS interval on 12q24.8 PCR was used to produce gene specific products for FISH (see below) and to produce exonic fragments for SSCP …

Background: Noonan syndrome (NS) and cardio-facio-cutaneous syndrome (CFC) are related disorders associated with disrupted RAS/RAF/MEK/ERK signalling. NS, characterised by facial dysmorphism, congenital heart defects and short stature, is caused by mutations in the genes PTPN11, SOS1 , KRAS and RAF1 . CFC is distinguished from NS by the presence of ectodermal abnormalities and more severe mental retardation in addition to the NS phenotype. The genetic aetiology of CFC was recently assigned to four genes: BRAF, KRAS, MEK1 and MEK2 . Methods: A comprehensive mutation analysis of BRAF, KRAS, MEK1 , MEK2 and SOS1 in 31 unrelated patients without mutations in PTPN11 is presented . Results: Mutations were identified in seven patients with CFC (two in BRAF , one in KRAS, one in MEK1 , two in MEK2 and one in SOS1 ). Two mutations were novel: MEK1 E203Q and MEK2 F57L. The SOS1 E433K mutation, identified in a patient diagnosed with CFC, has previously been reported in patients with NS. In one patient with NS, we also identified a mutation, BRAF K499E, that has previously been reported in patients with CFC. We thus suggest involvement of BRAF in the pathogenesis of NS also. Conclusions: Taken together, our results indicate that the molecular and clinical overlap between CFC and NS is more complex than previously suggested and that the syndromes might even represent allelic disorders. Furthermore, we suggest that the diagnosis should be refined to, for example, NS– PTPN11 -associated or CFC– BRAF -associated syndromes after the genetic defect has been established, as this may affect the prognosis and treatment of the patients.

Fetal jugular lymph sacs are accumulations of lymphatic fluid in the anterolateral region of the fetal neck. They may be isolated or occur in association with other structural anomalies and in some cases are presenting with an increased nuchal translucency or cystic hygroma. Their significance and the guidelines for the prenatal investigation when identified in the course of routine ultrasonography in pregnancy are still controversial. Our protocol for the investigation of these cases includes microarray analysis and DNA analysis for the Noonan syndrome panel. We report our experience with ten cases of prenatally diagnosed isolated fetal jugular neck cysts identified in the last 5 years (Table 1). In 10 cases identified by us in the last 5 years, 50% had a pathogenic mutation in a Noonan syndrome Panel, one had trisomy 21 and none had abnormality on microarray analysis (in the case with T21 we stopped the analysis following the QF-PCR results). However, all cases with abnormal results had NT > 3.5 mm or cystic hygroma. This study suggests that the identification of fetal jugular lymph sacs with an increased NT/cystic hygroma is associated with an increased incidence of Noonan syndrome and its related disorders and should instigate mutation analysis of the Noonan syndrome panel.

LEOPARD syndrome (LS) is a rare autosomal dominant disorder characterised by l entigines and cafe au lait spots, E KG anomalies, o cular hypertelorism, p ulmonary stenosis (PS), a bnormal genitalia, r etardation of growth, and d eafness, and has been successively considered as a distinct syndrome and later as a clinical variant of Noonan syndrome (NS). Some months after the discovery of heterozygous mutations in the PTPN11 gene in roughly 40% of clinically typical NS patients,1 Digilio et al 2 reported the presence of PTPN11 mutations in nine out of 10 unrelated patients with LS or NS with multiple lentigines or cafe au lait spots, confirming that both disorders are allelic variants. PTPN11 encodes SHP-2, a ubiquitously expressed non-receptor-type tyrosine phosphatase involved in a variety of cytokine and growth factor initiated signal transduction processes. SHP-2 contains two tandem SH2 domains encoded by exons 1 to 4 at the N terminus, and a phosphatase domain (PTP) encoded by exons 7 to 13 at the C terminus. Three different mutations have been described so far in LS, all located in the PTP domain.2–4 These mutations are believed to disrupt the interaction between the N-SH2 and PTP domains, leading to increased phosphatase activity as similarly observed in NS. However, mutations described in LS seems to be highly specific for this syndrome. In an attempt to better define the pattern of PTPN11 mutations responsible for LS and their correlation with clinical presentation, we here report results obtained in 14 families. DNA samples obtained from peripheral leucocytes of 14 unrelated propositi with a clinical diagnosis of LS were referred to our laboratory by confirmed clinician geneticists for PTPN11 mutation screening. For eight of them, parental DNA was also collected. Bi-directional direct sequencing of PTPN11 exons 2, 3, 4, 7, 8, 12, …

This is the first report of a Noonan syndrome patient who has had a vaginal rhabdomyosarcoma. Recent reports of Noonan syndrome patients with leukaemia have prompted speculation that there may be a slightly increased malignancy risk associated with this syndrome.

LEOPARD syndrome is an autosomal dominant disorder with multiple lentigines, congenital cardiac abnormalities, ocular hypertelorism, and retardation of growth. Deafness and genital abnormalities are less frequently found. We report a father and daughter and a third, unrelated patient with LEOPARD syndrome. Recently, missense mutations in the PTPN11 gene located in 12q24 were found to cause Noonan syndrome. All three cases of LEOPARD syndrome reported here have a Y279C mutation in the PTPN11 gene. We hypothesise that some PTPN11 mutations are associated with the typical Noonan syndrome phenotype and that other mutations, such as the Y279C mutation reported here, are associated with both the Noonan syndrome phenotype and with skin pigmentation anomalies, such as multiple lentigines or cafe au lait spots.

A male patient is reported with a 45,X karyotype and Leri-Weill dyschondrosteosis (LWD). FISH analysis with SHOX and SRY gene probes was carried out. One copy of both SHOX and SRY was detected in interphase nuclei, clarifying the origin of LWD and the male phenotype. Molecular results suggested that the 45,X karyotype arose through two independent events. The first occurred at paternal meiosis leading to an unequal crossing over between the short arms of the X and Y chromosomes. As a consequence, the SRY gene was translocated onto Xp, thereby explaining the male phenotype of the patient. The second event probably occurred at maternal meiosis or at the early stages of the zygote resulting in the loss of the maternal X chromosome. Keywords: 45,X karyotype; Leri-Weill syndrome; SHOX gene

Detailed clinical, ophthalmological, and molecular studies were performed on a multigeneration family in which there were many subjects with type 1 neurofibromatosis, a common autosomal dominant disorder. Affected family members displayed a wide range of clinical findings including, in two subjects, features seen in Noonan syndrome (triangular facies, downward slanting palpebral fissures, micrognathia, short stature, and learning disability). Subjects have been described previously whose features have overlapped with neurofibromatosis and Noonan syndrome, and it has been suggested that these persons might represent a separate condition. DNA haplotype analysis showed linkage of the neurofibromatosis phenotype seen in this family to the proximal long arm of chromosome 17 in the region where the type 1 neurofibromatosis gene has been mapped. These results imply that the Noonan phenotype seen in some patients with type 1 neurofibromatosis might be the result of variable or variant expression of the neurofibromatosis gene on chromosome 17. The possible role of non-specific factors, such as fetal hypotonia, in producing the neurofibromatosis-Noonan phenotype needs further investigation. The availability of closely linked and intragenic molecular markers for neurofibromatosis could potentially be useful in the diagnosis and characterisation of patients and families with atypical forms of neurofibromatosis.

The clinicogenetic relationship between Noonan syndrome (NS) and Noonan-like syndromes (Costello syndrome (CS), cardio-facio-cutaneous (CFC syndrome) and the disruption of the RAS-ERK pathway makes for a fascinating story that has developed over the past decade, and is still developing. The discovery that the genes causing these syndromes encode proteins that converge on the same metabolic pathway facilitated understanding of the similarities that group these conditions within one family of syndromes.1 Nevertheless, their nosological classification continues to be a challenge. There is general agreement that NS is caused by mutations of PTPN11 (most cases), SOS1 or RAF1 , that CFC syndrome is caused by mutations of BRAF (most cases), MEK1 or MEK2 , and that CS is caused …

Mutations in genes involved in Ras signalling cause Noonan syndrome and other disorders characterised by growth disturbances and variable neuro-cardio-facio-cutaneous features. We describe two sisters, 46 and 31 years old, who presented with dysmorphic features, hypotonia, feeding difficulties, retarded growth and psychomotor retardation early in life. The patients were initially diagnosed with Costello syndrome, and autosomal recessive inheritance was assumed. Remarkably, however, we identified a germline HRAS mutation (G12A) in one sister and a germline KRAS mutation (F156L) in her sibling. Both mutations had arisen de novo. The F156L mutant K-Ras protein accumulated in the active, guanosine triphosphate-bound conformation and affected downstream signalling. The patient harbouring this mutation was followed for three decades, and her cardiac hypertrophy gradually normalised. However, she developed severe epilepsy with hippocampal sclerosis and atrophy. The occurrence of distinct de novo mutations adds to variable expressivity and gonadal mosaicism as possible explanations of how an autosomal dominant disease may manifest as an apparently recessive condition.

We describe a 7 year old girl whose features satisfy the diagnosis of cardiofaciocutaneous syndrome. Her ectodermal features consist of fine, sparse hair, thin, opalescent nails, finger tip pads, generalised pigmentation of the skin, but no hyperkeratosis. Skin pigmentation and finger tip pads have not been previously reported in this syndrome. Twenty-two cases of CFC have been described but there is debate as to whether it is distinct from Noonan syndrome.

Noonan's syndrome is a clinically recognisable short stature syndrome with autosomal dominant inheritance. The diagnosis can be difficult as the phenotypic expression is very variable. There has been an attempt to divide this syndrome into type I (in which the facial features, especially ptosis, antimongoloid eye slant, and hypertelorism are prominent) and type II (where cardiological abnormalities are more to the fore), but this has not yet been confirmed by other studies.

We report a mother and two of her children, one female and the other male, who have ptosis, hypertelorism, epicanthic folds, downward slanting palpebral fissures, broad nasal bridge, and minor digital anomalies (fig 1); the children had delayed closure of a large anterior fontanelle. All three affected persons were born prematurely.