Clinical delineation, sex differences, and genotype-phenotype correlation in pathogenic KDM6A variants causing X-linked Kabuki syndrome type 2.

PURPOSE: The variant spectrum and the phenotype of X-linked Kabuki syndrome type 2 (KS2) are poorly understood. METHODS: Genetic and clinical details of new and published individuals with pathogenic KDM6A variants were compiled and analyzed. RESULTS: Sixty-one distinct pathogenic KDM6A variants (50 truncating, 11 missense) from 80 patients (34 males, 46 females) were identified. Missense variants clustered in the TRP 2, 3, 7 and Jmj-C domains. Truncating variants were significantly more likely to be de novo. Thirteen individuals had maternally inherited variants and one had a paternally inherited variant. Neonatal feeding difficulties, hypoglycemia, postnatal growth retardation, poor weight gain, motor delay, intellectual disability (ID), microcephaly, congenital heart anomalies, palate defects, renal malformations, strabismus, hearing loss, recurrent infections, hyperinsulinism, seizures, joint hypermobility, and gastroesophageal reflux were frequent clinical findings. Facial features of over a third of patients were not typical for KS. Males were significantly more likely to be born prematurely, have shorter stature, and severe developmental delay/ID. CONCLUSION: We expand the KDM6A variant spectrum and delineate the KS2 phenotype. We demonstrate that the variability of the KS2 phenotypic depends on sex and the variant type. We also highlight the overlaps and differences between the phenotypes of KS2 and KS1.

Recurrent De Novo Mutations Disturbing the GTP/GDP Binding Pocket of RAB11B Cause Intellectual Disability and a Distinctive Brain Phenotype.

The Rab GTPase family comprises ∼70 GTP-binding proteins, functioning in vesicle formation, transport and fusion. They are activated by a conformational change induced by GTP-binding, allowing interactions with downstream effectors. Here, we report five individuals with two recurrent de novo missense mutations in RAB11B; c.64G>A; p.Val22Met in three individuals and c.202G>A; p.Ala68Thr in two individuals. An overlapping neurodevelopmental phenotype, including severe intellectual disability with absent speech, epilepsy, and hypotonia was observed in all affected individuals. Additionally, visual problems, musculoskeletal abnormalities, and microcephaly were present in the majority of cases. Re-evaluation of brain MRI images of four individuals showed a shared distinct brain phenotype, consisting of abnormal white matter (severely decreased volume and abnormal signal), thin corpus callosum, cerebellar vermis hypoplasia, optic nerve hypoplasia and mild ventriculomegaly. To compare the effects of both variants with known inactive GDP- and active GTP-bound RAB11B mutants, we modeled the variants on the three-dimensional protein structure and performed subcellular localization studies. We predicted that both variants alter the GTP/GDP binding pocket and show that they both have localization patterns similar to inactive RAB11B. Evaluation of their influence on the affinity of RAB11B to a series of binary interactors, both effectors and guanine nucleotide exchange factors (GEFs), showed induction of RAB11B binding to the GEF SH3BP5, again similar to inactive RAB11B. In conclusion, we report two recurrent dominant mutations in RAB11B leading to a neurodevelopmental syndrome, likely caused by altered GDP/GTP binding that inactivate the protein and induce GEF binding and protein mislocalization.

Pathogenic variant in NFIX gene affecting three sisters due to paternal mosaicism.

We present a family with three girls presenting similar dysmorphic features, including overgrowth, intellectual disability, macrocephaly, prominent forehead, midface retrusion, strabismus, and scoliosis. Both parents were unaffected, suggesting the presence of an autosomal recessive syndrome. Following exome sequencing, a heterozygous nonsense variant was identified in the NFIX gene in all three siblings. The father appeared to have a low-grade (7%) mosaicism for this variant in his blood. Previously, de novo pathogenic variants in NFIX have been identified in Marshall-Smith syndrome and Malan syndrome, which share distinctive phenotypic features shared with the patients of the present family. This case emphasizes the importance of further molecular analysis especially in familial cases, to exclude the possibility of parental mosaicism.

Prenatal ultrasound findings of rasopathies in a cohort of 424 fetuses: update on genetic testing in the NGS era.

BACKGROUND: This study evaluates 6 years of prenatal rasopathy testing in the Netherlands, updates on previous data and gives recommendations for prenatal rasopathy testing. METHODS: 424 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. RESULTS: In 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. CONCLUSION: Fetuses 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.

Disruption of POGZ Is Associated with Intellectual Disability and Autism Spectrum Disorders.

Intellectual disability (ID) and autism spectrum disorders (ASD) are genetically heterogeneous, and a significant number of genes have been associated with both conditions. A few mutations in POGZ have been reported in recent exome studies; however, these studies do not provide detailed clinical information. We collected the clinical and molecular data of 25 individuals with disruptive mutations in POGZ by diagnostic whole-exome, whole-genome, or targeted sequencing of 5,223 individuals with neurodevelopmental disorders (ID primarily) or by targeted resequencing of this locus in 12,041 individuals with ASD and/or ID. The rarity of disruptive mutations among unaffected individuals (2/49,401) highlights the significance (p = 4.19 × 10(-13); odds ratio = 35.8) and penetrance (65.9%) of this genetic subtype with respect to ASD and ID. By studying the entire cohort, we defined common phenotypic features of POGZ individuals, including variable levels of developmental delay (DD) and more severe speech and language delay in comparison to the severity of motor delay and coordination issues. We also identified significant associations with vision problems, microcephaly, hyperactivity, a tendency to obesity, and feeding difficulties. Some features might be explained by the high expression of POGZ, particularly in the cerebellum and pituitary, early in fetal brain development. We conducted parallel studies in Drosophila by inducing conditional knockdown of the POGZ ortholog row, further confirming that dosage of POGZ, specifically in neurons, is essential for normal learning in a habituation paradigm. Combined, the data underscore the pathogenicity of loss-of-function mutations in POGZ and define a POGZ-related phenotype enriched in specific features.

The ARID1B spectrum in 143 patients: from nonsyndromic intellectual disability to Coffin-Siris syndrome.

PURPOSE: Pathogenic variants in ARID1B are one of the most frequent causes of intellectual disability (ID) as determined by large-scale exome sequencing studies. Most studies published thus far describe clinically diagnosed Coffin-Siris patients (ARID1B-CSS) and it is unclear whether these data are representative for patients identified through sequencing of unbiased ID cohorts (ARID1B-ID). We therefore sought to determine genotypic and phenotypic differences between ARID1B-ID and ARID1B-CSS. In parallel, we investigated the effect of different methods of phenotype reporting. METHODS: Clinicians entered clinical data in an extensive web-based survey. RESULTS: 79 ARID1B-CSS and 64 ARID1B-ID patients were included. CSS-associated dysmorphic features, such as thick eyebrows, long eyelashes, thick alae nasi, long and/or broad philtrum, small nails and small or absent fifth distal phalanx and hypertrichosis, were observed significantly more often (p < 0.001) in ARID1B-CSS patients. No other significant differences were identified. CONCLUSION: There are only minor differences between ARID1B-ID and ARID1B-CSS patients. ARID1B-related disorders seem to consist of a spectrum, and patients should be managed similarly. We demonstrated that data collection methods without an explicit option to report the absence of a feature (such as most Human Phenotype Ontology-based methods) tended to underestimate gene-related features.

Correction: The ARID1B spectrum in 143 patients: from nonsyndromic intellectual disability to Coffin-Siris syndrome.

The original version of this Article contained an error in the spelling of the author Pleuntje J. van der Sluijs, which was incorrectly given as Eline (P. J.) van der Sluijs. This has now been corrected in both the PDF and HTML versions of the Article.

First-year growth in children with Noonan syndrome: Associated with feeding problems?

Children with Noonan syndrome show rapid decline of growth in the first year of life and feeding problems are present in over 50%. The aim of this study was to explore whether growth decelerates because of feeding problems or other Noonan syndrome-related factors. We performed a retrospective, longitudinal cohort study of clinically and genetically diagnosed subjects with Noonan syndrome (n = 143). Questionnaires about the phenotypic-genotypic profile and reported feeding problems were sent to eligible subjects. Data on first-year growth was obtained from growth charts. Ninety-one participants were excluded because of different criteria. A total of 52 subjects with Noonan syndrome were included. The largest decline in weight and length standard deviation score (SDS) occurred in the first 2.5 months after birth (-1.93 and -1.15, respectively), with feeding problems causing a decline of 0.57 SDS in the remaining months. At 1 year, children with feeding problems were on average 290 g lighter and 0.8 cm shorter than children without feeding problems. Weight gain was also negatively influenced by having a PTPN11 mutation (n = 39) and a higher gestational age, whereas children of parents with Noonan syndrome and with a higher birth weight gained more weight. Growth in length was reduced by having cardiac surgery and a higher gestational age, but positively influenced by birth length and maternal height. Growth in children with Noonan syndrome is impaired right after birth and only partially associated with feeding problems. In addition, several specific Noonan syndrome-related factors seem to influence growth in the first year.

Genetic analysis of adults heterozygous for ALPL mutations.

Hypophosphatasia (HPP) is a rare inherited metabolic bone disease due to a deficiency of the tissue nonspecific alkaline phosphatase isoenzyme (TNSALP) encoded by the ALPL gene. Patients have consistently low serum alkaline phosphatase (AP), so that this parameter is a good hallmark of the disease. Adult HPP is heterogeneous, and some patients present only mild nonpathognomonic symptoms which are also common in the general population such as joint pain, osteomalacia and osteopenia, chondrocalcinosis, arthropathy and musculoskeletal pain. Adult HPP may be recessively or dominantly inherited; the latter case is assumed to be due to the dominant negative effect (DNE) of missense mutations derived from the functional homodimeric structure of TNSALP. However, there is no biological argument excluding the possibility of other causes of dominant HPP. Rheumatologists and endocrinologists are increasingly solicited for patients with low AP and nonpathognomonic symptoms of HPP. Many of these patients are heterozygous for an ALPL mutation and a challenging question is to determine if these symptoms, which are also common in the general population, are attributable to their heterozygous ALPL mutation or not. In an attempt to address this question, we reviewed a cohort of 61 adult patients heterozygous for an ALPL mutation. Mutations were distinguished according to their statistical likelihood to show a DNE. One-half of the patients carried mutations predicted with no DNE and were slightly less severely affected by the age of onset, serum AP activity and history of fractures. We hypothesized that these mutations result in another mechanism of dominance or are recessive alleles. To identify other genetic factors that could trigger the disease phenotype in heterozygotes for potential recessive mutations, we examined the next-generation sequencing results of 32 of these patients for a panel of 12 genes involved in the differential diagnosis of HPP or candidate modifier genes of HPP. The heterozygous genotype G/C of the COL1A2 coding SNP rs42524 c.1645C > G (p.Pro549Ala) was associated with the severity of the phenotype in patients carrying mutations with a DNE whereas the homozygous genotype G/G was over-represented in patients carrying mutations without a DNE, suggesting a possible role of this variant in the disease phenotype. These preliminary results support COL1A2 as a modifier gene of HPP and suggest that a significant proportion of adult heterozygotes for ALPL mutations may have unspecific symptoms not attributable to their heterozygosity.

Ocular findings in Noonan syndrome: a retrospective cohort study of 105 patients.

The aim of this retrospective study is to describe ocular findings in a large Noonan syndrome cohort and to detect associations between ocular features and genetic mutations that were not found in earlier studies. We collected ophthalmological and genetic data of 105 patients (median age, 12 years; range, 0-60 years) clinically diagnosed as Noonan syndrome. The ocular findings were linked to the genotypes. All patients with Noonan syndrome showed multiple abnormalities in the categories of vision and refraction, external ocular features, ocular alignment and motility, anterior ocular segment, and posterior ocular segment. In total, 50 patients have NS due to a mutation in PTPN11. Permanent visual impairment (bilateral best-corrected visual acuity < 0.3) was found in 7 patients, including patients with a mutation in RAF1, SHOC2, and KRAS. Keratoconus was found in 2 PTPN11 positive patients, and prominent corneal nerves were observed in a patient with a SOS1 mutation. CONCLUSIONS: This study shows an overview of ocular abnormalities in Noonan syndrome, including permanent visual impairment caused by binocular optic nerve abnormalities and nystagmus. Delay in ophthalmological diagnosis is still present, also in patients with visual impairment. All Noonan syndrome patients should have a complete ophthalmological examination at the time of diagnosis. What is Known: • Although we discover more pathogenic mutations in patients with Noonan syndrome, Noonan syndrome still is a clinical diagnosis • Ocular features of Noonan syndrome are characterized by developmental anomalies of the eyelids and associated with other ocular abnormalities in childhood (including refractive errors, strabismus and amblyopia). What is New: • There seems to be a delay in the ophthalmological diagnosis and awareness of the broad variety ofophthalmological features including refractive errors and visual impairment in Noonan syndrome is needed. All children should have a full ophthalmological examination at the time of diagnosis. • Permanent visual impairment (best-corrected visual acuity < 0.3) is found in patients with mutations in RAF1, SHOC2, and KRAS and the cause is probably a developmental disorder of the optic nerves.

Variable phenotypic expression in a large Noonan syndrome family segregating a novel SOS1 mutation.

Noonan syndrome (NS) is an autosomal dominant multisystem condition with a variable phenotype. The most characteristic features are short stature, congenital heart defects, and recognizable facial features. Mutations in SOS1 are found in 10-20% of patients with NS. Different genotype-phenotype studies mention correlations between SOS1 mutations and some features, such as ectodermal abnormalities and specific facial features. We present a large NS family with a novel pathogenic mutation; SOS1 c.3134C>G, p.Pro1045Arg. Ten family members with NS are included with genetically confirmed mutation and clinical evaluation. The phenotype shows a broad spectrum from only few suggestive features for NS in the older generation to typical features in the youngest generation. We report on a novel pathogenic mutation in the SOS1 gene and a large clinical spectrum in a NS family with ten genetically confirmed affected individuals.

Motor performance in children with Noonan syndrome.

Although problems with motor performance in daily life are frequently mentioned in Noonan syndrome, the motor performance profile has never been systematically investigated. The aim of this study was to examine whether a specific profile in motor performance in children with Noonan syndrome was seen using valid norm-referenced tests. The study assessed motor performance in 19 children with Noonan syndrome (12 females, mean age 9 years 4 months, range 6 years 1 month to 11 years and 11 months, SDS 1 year and 11 months). More than 60% of the parents of the children reported pain, decreased muscle strength, reduced endurance, and/or clumsiness in daily functioning. The mean standard scores on the Visual Motor Integration (VMI) test and Movement Assessment Battery for Children 2, Dutch version (MABC-2-NL) items differed significantly from the reference scores. Grip strength, muscle force, and 6 min Walking Test (6 MWT) walking distance were significantly lower, and the presence of generalized hypermobility was significantly higher. All MABC-2-NL scores (except manual dexterity) correlated significantly with almost all muscle strength tests, VMI total score, and VMI visual perception score. The 6 MWT was only significantly correlated to grip strength. This is the first study that confirms that motor performance, strength, and endurance are significantly impaired in children with Noonan syndrome. Decreased functional motor performance seems to be related to decreased visual perception and reduced muscle strength. Research on causal relationships and the effectiveness of interventions is needed. Physical and/or occupational therapy guidance should be considered to enhance participation in daily life.

Activating mutations in RRAS underlie a phenotype within the RASopathy spectrum and contribute to leukaemogenesis.

RASopathies, a family of disorders characterized by cardiac defects, defective growth, facial dysmorphism, variable cognitive deficits and predisposition to certain malignancies, are caused by constitutional dysregulation of RAS signalling predominantly through the RAF/MEK/ERK (MAPK) cascade. We report on two germline mutations (p.Gly39dup and p.Val55Met) in RRAS, a gene encoding a small monomeric GTPase controlling cell adhesion, spreading and migration, underlying a rare (2 subjects among 504 individuals analysed) and variable phenotype with features partially overlapping Noonan syndrome, the most common RASopathy. We also identified somatic RRAS mutations (p.Gly39dup and p.Gln87Leu) in 2 of 110 cases of non-syndromic juvenile myelomonocytic leukaemia, a childhood myeloproliferative/myelodysplastic disease caused by upregulated RAS signalling, defining an atypical form of this haematological disorder rapidly progressing to acute myeloid leukaemia. Two of the three identified mutations affected known oncogenic hotspots of RAS genes and conferred variably enhanced RRAS function and stimulus-dependent MAPK activation. Expression of an RRAS mutant homolog in Caenorhabditis elegans enhanced RAS signalling and engendered protruding vulva, a phenotype previously linked to the RASopathy-causing SHOC2(S2G) mutant. Overall, these findings provide evidence of a functional link between RRAS and MAPK signalling and reveal an unpredicted role of enhanced RRAS function in human disease.

Ocular Manifestations of Noonan Syndrome: A Prospective Clinical and Genetic Study of 25 Patients.

PURPOSE: To determine the full spectrum of ocular manifestations in patients with Noonan syndrome (NS). DESIGN: Prospective cross-sectional clinical and genetic study in a tertiary referral center. PARTICIPANTS: Twenty-five patients with NS (mean age, 14 years; range, 8 months-25 years) clinically diagnosed by validated criteria. METHODS: All patients were examined by the same team following a detailed study protocol. Genetic analyses were performed in 23 patients. MAIN OUTCOME MEASURES: Ocular abnormalities of vision and refraction, external ocular features, ocular position and motility, anterior segment, posterior segment, and intraocular pressure. RESULTS: Ocular features of vision and refraction were amblyopia (32%), myopia (40%), and astigmatism (52%). External ocular features were epicanthic folds (84%), hypertelorism (68%), ptosis (56%), high upper eyelid crease (64%), lower eyelid retraction (60%), abnormal upward slanting palpebral fissures (36%), downward slanting palpebral fissures (32%), and lagophthalmos (28%). Orthoptic abnormalities included strabismus (40%), abnormal stereopsis (44%), and limited ocular motility (40%). Anterior segment abnormalities included prominent corneal nerves (72%) and posterior embryotoxon (32%). Additional ocular features were found, including nonglaucomatous optic disc excavation (20%), relatively low (<10 mmHg) intraocular pressure (22%), and optic nerve hypoplasia (4%). Mutations were established in 22 patients: 19 PTPN11 mutations (76%), 1 SOS1 mutation, 1 BRAF mutation, and 1 KRAS mutation. The patient with the highest number of prominent corneal nerves had an SOS1 mutation. The patient with the lowest visual acuity, associated with bilateral optic nerve hypoplasia, had a BRAF mutation. Patients with severe ptosis and nearly total absence of levator muscle function had PTPN11 mutations. All patients showed at least 3 ocular features (range, 3-13; mean, 7), including at least 1 external ocular feature in more than 95% of the patients. CONCLUSIONS: Noonan syndrome is a clinical diagnosis with multiple genetic bases associated with an extensive variety of congenital ocular abnormalities. Ocular features of NS are characterized by 1 or more developmental anomalies of the eyelids (involving the position, opening, and closure) associated with various other ocular abnormalities in childhood, including amblyopia, myopia, astigmatism, strabismus, limited ocular motility, prominent corneal nerves, and posterior embryotoxon.

Perceived motor problems in daily life: Focus group interviews with people with Noonan syndrome and their relatives.

Studies from a patient perspective on motor performance problems in Noonan syndrome in daily life are lacking. The aims of this study were to provide insight into the motor performance problems that people with Noonan syndrome and/or their relatives experienced, the major consequences they suffered, the benefits of interventions they experienced, and the experiences with healthcare professionals they mentioned. We interviewed 10 adults with Noonan syndrome (two were joined by their parent), and 23 mothers (five of whom had Noonan syndrome), nine fathers (one of whom had Noonan syndrome) and one cousin who reported on 28 children with Noonan syndrome. People with Noonan syndrome reported particular problems related to pain, decreased muscle strength, fatigue, and clumsiness, which had an evident impact on functioning in daily life. Most participants believed that problems with motor performance improved with exercise, appropriate physiotherapy guidance, and other supportive interventions. Nevertheless, people with Noonan syndrome and/or their relatives did not feel heard and supported and experienced no understanding of their problems by healthcare professionals. This was the first study from a patient perspective that described the motor performance problems in people with Noonan syndrome, the major consequences in daily life, the positive experiences of interventions and the miscommunication with healthcare professionals. To achieve optimal support, healthcare professionals, as well as people with Noonan syndrome and/or their relatives themselves, should be aware of these frequently presented problems with motor performance. Research on these different aspects is needed to better understand and support people with Noonan syndrome.© 2016 Wiley Periodicals, Inc.

Germline KRAS mutations cause Noonan syndrome.

Noonan syndrome (MIM 163950) is characterized by short stature, facial dysmorphism and cardiac defects. Heterozygous mutations in PTPN11, which encodes SHP-2, cause approximately 50% of cases of Noonan syndrome. The SHP-2 phosphatase relays signals from activated receptor complexes to downstream effectors, including Ras. We discovered de novo germline KRAS mutations that introduce V14I, T58I or D153V amino acid substitutions in five individuals with Noonan syndrome and a P34R alteration in a individual with cardio-facio-cutaneous syndrome (MIM 115150), which has overlapping features with Noonan syndrome. Recombinant V14I and T58I K-Ras proteins show defective intrinsic GTP hydrolysis and impaired responsiveness to GTPase activating proteins, render primary hematopoietic progenitors hypersensitive to growth factors and deregulate signal transduction in a cell lineage-specific manner. These studies establish germline KRAS mutations as a cause of human disease and infer that the constellation of developmental abnormalities seen in Noonan syndrome spectrum is, in large part, due to hyperactive Ras.

Identification of mutations in CUL7 in 3-M syndrome.

Intrauterine growth retardation is caused by maternal, fetal or placental factors that result in impaired endovascular trophoblast invasion and reduced placental perfusion. Although various causes of intrauterine growth retardation have been identified, most cases remain unexplained. Studying 29 families with 3-M syndrome (OMIM 273750), an autosomal recessive condition characterized by severe pre- and postnatal growth retardation, we first mapped the underlying gene to chromosome 6p21.1 and then identified 25 distinct mutations in the gene cullin 7 (CUL7). CUL7 assembles an E3 ubiquitin ligase complex containing Skp1, Fbx29 (also called Fbw8) and ROC1 and promotes ubiquitination. Using deletion analysis, we found that CUL7 uses its central region to interact with the Skp1-Fbx29 heterodimer. Functional studies indicated that the 3-M-associated CUL7 nonsense and missense mutations R1445X and H1464P, respectively, render CUL7 deficient in recruiting ROC1. These results suggest that impaired ubiquitination may have a role in the pathogenesis of intrauterine growth retardation in humans.

Heterozygous germline mutations in the CBL tumor-suppressor gene cause a Noonan syndrome-like phenotype.

RAS signaling plays a key role in controlling appropriate cell responses to extracellular stimuli and participates in early and late developmental processes. Although enhanced flow through this pathway has been established as a major contributor to oncogenesis, recent discoveries have revealed that aberrant RAS activation causes a group of clinically related developmental disorders characterized by facial dysmorphism, a wide spectrum of cardiac disease, reduced growth, variable cognitive deficits, ectodermal and musculoskeletal anomalies, and increased risk for certain malignancies. Here, we report that heterozygous germline mutations in CBL, a tumor-suppressor gene that is mutated in myeloid malignancies and encodes a multivalent adaptor protein with E3 ubiquitin ligase activity, can underlie a phenotype with clinical features fitting or partially overlapping Noonan syndrome (NS), the most common condition of this disease family. Independent CBL mutations were identified in two sporadic cases and two families from among 365 unrelated subjects who had NS or suggestive features and were negative for mutations in previously identified disease genes. Phenotypic heterogeneity and variable expressivity were documented. Mutations were missense changes altering evolutionarily conserved residues located in the RING finger domain or the linker connecting this domain to the N-terminal tyrosine kinase binding domain, a known mutational hot spot in myeloid malignancies. Mutations were shown to affect CBL-mediated receptor ubiquitylation and dysregulate signal flow through RAS. These findings document that germline mutations in CBL alter development to cause a clinically variable condition that resembles NS and that possibly predisposes to malignancies.

Noonan syndrome, the SOS1 gene and embryonal rhabdomyosarcoma.

Noonan Syndrome (NS) is an autosomal dominant condition characterized by short stature, facial dysmorphisms, and congenital heart defects, and is caused by mutations in either PTPN11, KRAS, NRAS, SHOC2, RAF1, or SOS1. Furthermore, NS is known for its predisposition to develop cancer, particularly hematological malignancies and specific solid tumors, mainly neuroblastoma and embryonal rhabdomyosacroma (ERMS). Until recently, however, cancer predisposition in NS patients with SOS1 mutations was not reported. Here we present a NS patient with a de novo germline SOS1 mutation (p.Lys728Ile) and ERMS. This heterozygous germline mutation was homozygously present in the ERMS of this patient due to an acquired uniparental disomy (UPD) of chromosome 2. In addition, several other chromosomal aberrations were encountered, some of which are known to recurrently occur in ERMS. Sequence analysis of the SOS1 gene in 20 sporadic ERMS tumors failed to reveal any pathogenic mutations, implicating that SOS1 is not a major player in the development of this tumor outside the context of NS.