Angelo Selicorni

Gain-of-function RAF1 mutations cause Noonan and LEOPARD syndromes with hypertrophic cardiomyopathy

Noonan and LEOPARD syndromes are developmental disorders with overlapping features, including cardiac abnormalities, short stature and facial dysmorphia. Increased RAS signaling owing to PTPN11, SOS1 and KRAS mutations causes ∼60% of Noonan syndrome cases, and PTPN11 mutations cause 90% of LEOPARD syndrome cases. Here, we report that 18 of 231 individuals with Noonan syndrome without known mutations (corresponding to 3% of all affected individuals) and two of six individuals with LEOPARD syndrome without PTPN11 mutations have missense mutations in RAF1, which encodes a serine-threonine kinase that activates MEK1 and MEK2. Most mutations altered a motif flanking Ser259, a residue critical for autoinhibition of RAF1 through 14-3-3 binding. Of 19 subjects with a RAF1 mutation in two hotspots, 18 (or 95%) showed hypertrophic cardiomyopathy (HCM), compared with the 18% prevalence of HCM among individuals with Noonan syndrome in general. Ectopically expressed RAF1 mutants from the two HCM hotspots had increased kinase activity and enhanced ERK activation, whereas non–HCM-associated mutants were kinase impaired. Our findings further implicate increased RAS signaling in pathological cardiomyocyte hypertrophy.

X-linked Cornelia de Lange syndrome owing to SMC1L1 mutations.

Cornelia de Lange syndrome is a multisystem developmental disorder characterized by facial dysmorphisms, upper limb abnormalities, growth delay and cognitive retardation. Mutations in the NIPBL gene, a component of the cohesin complex, account for approximately half of the affected individuals. We report here that mutations in SMC1L1 (also known as SMC1), which encodes a different subunit of the cohesin complex, are responsible for CdLS in three male members of an affected family and in one sporadic case.

Mutation of SHOC2 promotes aberrant protein N-myristoylation and causes Noonan-like syndrome with loose anagen hair

N-myristoylation is a common form of co-translational protein fatty acylation resulting from the attachment of myristate to a required N-terminal glycine residue. We show that aberrantly acquired N-myristoylation of SHOC2, a leucine-rich repeat–containing protein that positively modulates RAS-MAPK signal flow, underlies a clinically distinctive condition of the neuro-cardio-facial-cutaneous disorders family. Twenty-five subjects with a relatively consistent phenotype previously termed Noonan-like syndrome with loose anagen hair (MIM607721) shared the 4A>G missense change in SHOC2 (producing an S2G amino acid substitution) that introduces an N-myristoylation site, resulting in aberrant targeting of SHOC2 to the plasma membrane and impaired translocation to the nucleus upon growth factor stimulation. Expression of SHOC2S2G in vitro enhanced MAPK activation in a cell type–specific fashion. Induction of SHOC2S2G in Caenorhabditis elegans engendered protruding vulva, a neomorphic phenotype previously associated with aberrant signaling. These results document the first example of an acquired N-terminal lipid modification of a protein causing human disease.

Heterozygous submicroscopic inversions involving olfactory receptor-gene clusters mediate the recurrent t(4;8)(p16;p23) translocation.

The t(4;8)(p16;p23) translocation, in either the balanced form or the unbalanced form, has been reported several times. Taking into consideration the fact that this translocation may be undetected in routine cytogenetics, we find that it may be the most frequent translocation after t(11q;22q), which is the most common reciprocal translocation in humans. Case subjects with der(4) have the Wolf-Hirschhorn syndrome, whereas case subjects with der(8) show a milder spectrum of dysmorphic features. Two pairs of the many olfactory receptor (OR)-gene clusters are located close to each other, on both 4p16 and 8p23. Previously, we demonstrated that an inversion polymorphism of the OR region at 8p23 plays a crucial role in the generation of chromosomal imbalances through unusual meiotic exchanges. These findings prompted us to investigate whether OR-related inversion polymorphisms at 4p16 and 8p23 might also be involved in the origin of the t(4;8)(p16;p23) translocation. In seven case subjects (five of whom both represented de novo cases and were of maternal origin), including individuals with unbalanced and balanced translocations, we demonstrated that the breakpoints fell within the 4p and 8p OR-gene clusters. FISH experiments with appropriate bacterial-artificial-chromosome probes detected heterozygous submicroscopic inversions of both 4p and 8p regions in all the five mothers of the de novo case subjects. Heterozygous inversions on 4p16 and 8p23 were detected in 12.5% and 26% of control subjects, respectively, whereas 2.5% of them were scored as doubly heterozygous. These novel data emphasize the importance of segmental duplications and large-scale genomic polymorphisms in the evolution and pathology of the human genome.

Germline BRAF mutations in noonan, LEOPARD, and cardiofaciocutaneous Syndromes: Molecular diversity and associated phenotypic spectrum

Noonan, LEOPARD, and cardiofaciocutaneous syndromes (NS, LS, and CFCS) are developmental disorders with overlapping features including distinctive facial dysmorphia, reduced growth, cardiac defects, skeletal and ectodermal anomalies, and variable cognitive deficits. Dysregulated RAS–mitogen‐activated protein kinase (MAPK) signal traffic has been established to represent the molecular pathogenic cause underlying these conditions. To investigate the phenotypic spectrum and molecular diversity of germline mutations affecting BRAF, which encodes a serine/threonine kinase functioning as a RAS effector frequently mutated in CFCS, subjects with a diagnosis of NS (N=270), LS (N=6), and CFCS (N=33), and no mutation in PTPN11, SOS1, KRAS, RAF1, MEK1, or MEK2, were screened for the entire coding sequence of the gene. Besides the expected high prevalence of mutations observed among CFCS patients (52%), a de novo heterozygous missense change was identified in one subject with LS (17%) and five individuals with NS (1.9%). Mutations mapped to multiple protein domains and largely did not overlap with cancer‐associated defects. NS‐causing mutations had not been documented in CFCS, suggesting that the phenotypes arising from germline BRAF defects might be allele specific. Selected mutant BRAF proteins promoted variable gain of function of the kinase, but appeared less activating compared to the recurrent cancer‐associated p.Val600Glu mutant. Our findings provide evidence for a wide phenotypic diversity associated with mutations affecting BRAF, and occurrence of a clinical continuum associated with these molecular lesions. Hum Mutat 0:1–8, 2009.

Cornelia de Lange syndrome: clinical review, diagnostic and scoring systems, and anticipatory guidance.

Cornelia de Lange syndrome (CdLS), also known as Brachmann‐de Lange syndrome, is a well‐described multiple malformation syndrome typically involving proportionate small stature, developmental delay, specific facial features, major malformations (particularly the cardiac, gastrointestinal and musculoskeletal systems), and behavioral abnormalities. There is a broad spectrum of clinical involvement, with increasing recognition of a much milder phenotype than previously recognized. Significant progress has been made in recent years in the clinical and molecular delineation of CdLS, necessitating a revision of the diagnostic criteria, more inclusive of the milder cases. In addition, a scoring system of severity has been found to correlate with specific brain changes. Thus, a clinical overview and recommendations for anticipatory guidance are timely in aiding caretakers and professionals to individualize care decisions and maximize developmental potential for individuals with CdLS. These guidelines are derived from consensus based on collective experience of over 500 patients with CdLS, observations of the natural history in children, adolescents, and adults, a review of the literature, and contacts with national support organizations in North America and Europe.

Mutations in the DNA methyltransferase gene, DNMT3A, cause an overgrowth syndrome with intellectual disability

Overgrowth disorders are a heterogeneous group of conditions characterized by increased growth parameters and other variable clinical features such as intellectual disability and facial dysmorphism. To identify new causes of human overgrowth, we performed exome sequencing in ten proband-parent trios and detected two de novo DNMT3A mutations. We identified 11 additional de novo mutations by sequencing DNMT3A in a further 142 individuals with overgrowth. The mutations alter residues in functional DNMT3A domains, and protein modeling suggests that they interfere with domain-domain interactions and histone binding. Similar mutations were not present in 1,000 UK population controls (13/152 cases versus 0/1,000 controls; P < 0.0001). Mutation carriers had a distinctive facial appearance, intellectual disability and greater height. DNMT3A encodes a DNA methyltransferase essential for establishing methylation during embryogenesis and is commonly somatically mutated in acute myeloid leukemia. Thus, DNMT3A joins an emerging group of epigenetic DNA- and histone-modifying genes associated with both developmental growth disorders and hematological malignancies.Overgrowth disorders are a heterogeneous group of conditions characterized by increased growth parameters and other variable clinical features such as intellectual disability and facial dysmorphism. To identify new causes of human overgrowth, we performed exome sequencing in ten proband-parent trios and detected two de novo DNMT3A mutations. We identified 11 additional de novo mutations by sequencing DNMT3A in a further 142 individuals with overgrowth. The mutations alter residues in functional DNMT3A domains, and protein modeling suggests that they interfere with domain-domain interactions and histone binding. Similar mutations were not present in 1,000 UK population controls (13/152 cases versus 0/1,000 controls; P < 0.0001). Mutation carriers had a distinctive facial appearance, intellectual disability and greater height. DNMT3A encodes a DNA methyltransferase essential for establishing methylation during embryogenesis and is commonly somatically mutated in acute myeloid leukemia. Thus, DNMT3A joins an emerging group of epigenetic DNA- and histone-modifying genes associated with both developmental growth disorders and hematological malignancies.

A balanced chromosomal translocation disrupting ARHGEF9 is associated with epilepsy, anxiety, aggression, and mental retardation

Clustering of inhibitory γ‐aminobutyric acidA (GABAA) and glycine receptors at synapses is thought to involve key interactions between the receptors, a “scaffolding” protein known as gephyrin and the RhoGEF collybistin. We report the identification of a balanced chromosomal translocation in a female patient presenting with a disturbed sleep‐wake cycle, late‐onset epileptic seizures, increased anxiety, aggressive behavior, and mental retardation, but not hyperekplexia. Fine mapping of the breakpoint indicates disruption of the collybistin gene (ARHGEF9) on chromosome Xq11, while the other breakpoint lies in a region of 18q11 that lacks any known or predicted genes. We show that defective collybistin transcripts are synthesized and exons 7–10 are replaced by cryptic exons from chromosomes X and 18. These mRNAs no longer encode the pleckstrin homology (PH) domain of collybistin, which we now show binds phosphatidylinositol‐3‐phosphate (PI3P/PtdIns‐3‐P), a phosphoinositide with an emerging role in membrane trafficking and signal transduction, rather than phosphatidylinositol 3,4,5‐trisphosphate (PIP3/PtdIns‐3,4,5‐P) as previously suggested in the “membrane activation model” of gephyrin clustering. Consistent with this finding, expression of truncated collybistin proteins in cultured neurons interferes with synaptic localization of endogenous gephyrin and GABAA receptors. These results suggest that collybistin has a key role in membrane trafficking of gephyrin and selected GABAA receptor subtypes involved in epilepsy, anxiety, aggression, insomnia, and learning and memory. Hum Mutat 0,1–9, 2008.

Seizure and EEG Patterns in Angelman's Syndrome

We studied the seizure and polygraphic patterns of 18 patients with Angelmans syndrome. All patients showed movement problems. Eleven patients were also reported to have long-lasting periods of jerky movements. The polygraphic recording showed a myoclonic status epilepticus in nine of them. Seven patients had partial seizures with eye deviation and vomiting, similar to those of childhood occipital epilepsies. These seizures and electroencephalographic patterns suggest that Angelmans syndrome occurs in most of the patients as a nonprogressive, age-dependent myoclonic encephalopathy with a prominent occipital involvement. These findings indicate that, whereas ataxia is a constant symptom in Angelmans syndrome, the occurrence of a transient myoclonic status epilepticus may account for the recurrence of different abnormal movements, namely the jerky ones. (J Child Neurol 1995;10:467-471).

Gastroesophageal reflux and Cornelia de Lange syndrome: Typical and atypical symptoms

As previously reported, gastroesophageal reflux (GER) is a frequent and severe medical complication of Cornelia de Lange syndrome (CDLS). The incidence of GER and the correlation between its presence and degree, and the clinical phenotype of CDLS (mild/classical according to Van Allen classification) were evaluated in a series of 43 patients. The pattern of presenting symptoms and their clinical evolution after medical or surgical treatment were also studied. A pathological GER was evident in 28/43 (65%) CDLS patients. The incidence of the complication was not significantly different in patients with classical (93.3%) vs. mild phenotype (82.3%), whereas a strong correlation was present between the degree of the esophageal damage and the clinical phenotype. A behavioral symptom (hyperactivity) was the most frequent sign associated with the condition (85%). Our data confirm the high occurrence of GER in CDLS patients, independently from the CDLS clinical phenotype. Regarding the severity of the esophageal lesions, a significant difference between the two clinical CDLS phenotypes was found. The evaluation of the presenting symptoms and of their evolution during the treatment emphasizes the importance of behavioral symptoms as major signs of esophageal damage in CDLS.