Bruno Marino

22q11.2 Deletion Syndrome

22q11.2 deletion syndrome (22q11.2DS) is the most common chromosomal microdeletion disorder, estimated to result mainly from de novo non-homologous meiotic recombination events occurring in approximately 1 in every 1,000 fetuses. The first description in the English language of the constellation of findings now known to be due to this chromosomal difference was made in the 1960s in children with DiGeorge syndrome, who presented with the clinical triad of immunodeficiency, hypoparathyroidism and congenital heart disease. The syndrome is now known to have a heterogeneous presentation that includes multiple additional congenital anomalies and later-onset conditions, such as palatal, gastrointestinal and renal abnormalities, autoimmune disease, variable cognitive delays, behavioural phenotypes and psychiatric illness — all far extending the original description of DiGeorge syndrome. Management requires a multidisciplinary approach involving paediatrics, general medicine, surgery, psychiatry, psychology, interventional therapies (physical, occupational, speech, language and behavioural) and genetic counselling. Although common, lack of recognition of the condition and/or lack of familiarity with genetic testing methods, together with the wide variability of clinical presentation, delays diagnosis. Early diagnosis, preferably prenatally or neonatally, could improve outcomes, thus stressing the importance of universal screening. Equally important, 22q11.2DS has become a model for understanding rare and frequent congenital anomalies, medical conditions, psychiatric and developmental disorders, and may provide a platform to better understand these disorders while affording opportunities for translational strategies across the lifespan for both patients with 22q11.2DS and those with these associated features in the general population.

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.

Grouping of Multiple-Lentigines/LEOPARD and Noonan Syndromes on the PTPN11 Gene

Multiple-lentigines (ML)/LEOPARD (multiple lentigines, electrocardiographic-conduction abnormalities, ocular hypertelorism, pulmonary stenosis, abnormal genitalia, retardation of growth, and sensorineural deafness) syndrome is an autosomal dominant condition--characterized by lentigines and café au lait spots, facial anomalies, cardiac defects--that shares several clinical features with Noonan syndrome (NS). We screened nine patients with ML/LEOPARD syndrome (including a mother-daughter pair) and two children with NS who had multiple café au lait spots, for mutations in the NS gene, PTPN11, and found, in 10 of 11 patients, one of two new missense mutations, in exon 7 or exon 12. Both mutations affect the PTPN11 phosphotyrosine phosphatase domain, which is involved in <30% of the NS PTPN11 mutations. The study demonstrates that ML/LEOPARD syndrome and NS are allelic disorders. The detected mutations suggest that distinct molecular and pathogenetic mechanisms cause the peculiar cutaneous manifestations of the ML/LEOPARD-syndrome subtype of NS.

Loss-of-function mutations in the EGF-CFC gene CFC1 are associated with human left-right laterality defects

All vertebrates display a characteristic asymmetry of internal organs with the cardiac apex, stomach and spleen towards the left, and the liver and gall bladder on the right. Left-right (L-R) axis abnormalities or laterality defects are common in humans (1 in 8,500 live births). Several genes (such as Nodal, Ebaf and Pitx2) have been implicated in L-R organ positioning in model organisms. In humans, relatively few genes have been associated with a small percentage of human situs defects. These include ZIC3 (ref. 5), LEFTB (formerly LEFTY2; ref. 6) and ACVR2B (encoding activin receptor IIB; ref. 7). The EGF-CFC genes, mouse Cfc1 (encoding the Cryptic protein; ref. 9) and zebrafish one-eyed pinhead (oep; refs 10, 11) are essential for the establishment of the L-R axis. EGF-CFC proteins act as co-factors for Nodal-related signals, which have also been implicated in L-R axis development. Here we identify loss-of-function mutations in human CFC1 (encoding the CRYPTIC protein) in patients with heterotaxic phenotypes (randomized organ positioning). The mutant proteins have aberrant cellular localization in transfected cells and are functionally defective in a zebrafish oep-mutant rescue assay. Our findings indicate that the essential role of EGF-CFC genes and Nodal signalling in left-right axis formation is conserved from fish to humans. Moreover, our results support a role for environmental and/or genetic modifiers in determining the ultimate phenotype in humans.

Practical guidelines for managing patients with 22q11.2 deletion syndrome

A 12-year-old boy currently is followed by multiple sub-specialists for problems caused by the chromosome 22q11.2 deletion syndrome (22q11DS) (Figure). He was born via spontaneous vaginal delivery, weighing 3033 g, to a 31-year-old G3P3 mother after a full-term pregnancy complicated only by mild polyhydramnios. Family history was non-contributory. Apgar scores were 8 at 1 minute and 9 at 5 minutes. With the exception of a weak cry, the results of the infant’s initial examination were unremarkable, and he was moved to the well-baby nursery. Shortly thereafter, a cardiac murmur was noted, the cardiology department was consulted, and the child was transferred to a local tertiary care facility with a diagnosis of tetralogy of Fallot. Stable, he was discharged home at 3 days of life. Figure Mild dysmorphic facial features of a boy aged 11 years with 22q11.2DS, including a short forehead, hooded eyelids with upslanting palpebral fissures, malar flatness, bulbous nasal tip with hypoplastic alae nasi, and protuberant ears. At 5 days of life, he had jerky movements. On presentation to the local emergency department, his total calcium level was 4.7 mg/dL, and later partial hypoparathyroidism was diagnosed. At that time, a consulting geneticist suggested the diagnosis of chromosome 22q11DS. Weeks later, the family received a telephone call confirming the diagnosis with fluorescence in situ hybridization (FISH). No additional information about the diagnosis, prognosis, etiology, or recurrence risk was provided until the child was 5 months of age, when he underwent cardiac repair at a third hospital, where a comprehensive 22q11DS program was in operation. In the interim, the child had feeding difficulties requiring supplemental nasogastric tube feeds, nasal regurgitation, and gastroesophageal reflux, while the parents searched the internet for reliable information about their son’s diagnosis. Subsequent notable abnormalities and interventions included: recurrent otitis media with bilateral myringotomy tube placement at 6 months; angioplasty with left pulmonary artery stent placement after the identification of pulmonary artery stenosis with bilateral pleural effusions at age 6 years; chronic upper respiratory infections with significant T cell dysfunction requiring live viral vaccines to be held until age 7 years; velopharyngeal incompetence necessitating posterior pharyngeal flap surgery at 7 years; enamel hypoplasia and numerous caries resulting in 3 separate dental procedures under general cardiac anesthesia beginning at age 7 years; multiple cervical and thoracic vertebral anomalies with thoracic levoconvex scoliosis and upper lumbar dextroscoliosis requiring growing rod placement at age 11 years with subsequent rod extension at ages 11.5 and 12 years; postoperative hypocalcemia; short stature; constipation; and persistent idiopathic thrombocytopenia. Pertinent negative test results included normal renal ultrasound scanning and parental 22q11.2 deletion studies. On physical examination, the boy’s height and weight have consistently tracked just below the fifth percentile, with no evidence of growth hormone deficiency. His head circumference is within reference range at the 25th percentile. Dysmorphic features include: a low anterior hairline; hooded eyelids; malar flatness; normally formed but protuberant ears with attached lobes; a mildly deviated nose with a bulbous nasal tip and hypoplastic alae nasi; asymmetric crying facies with a thin upper lip; mild micrognathia; a sacral dimple; and soft tissue syndactyly of the second and third toes. Developmentally, the boy had mild delays in achieving motor milestones, sitting at 11 months and walking at 18 months. However, he exhibited significant delays in the emergence of language: he never babbled, spoke his first words at age 3 years, and only achieved full conversational speech at 7 years. However, he had relative strengths in receptive language and communicated appropriately by the use of sign language. Now quite conversant, he is mainstreamed in the seventh grade with resource room supports. Moreover, he is affable, but exhibits anxiety and perseverations. Lastly, despite numerous medical, academic, and social challenges, he participates in assisted athletics, is an avid wrestling fan, and enjoys travel. However, his exceptionally supportive parents, siblings, and extended family continue to worry about his long-term outcome and transition of care as he approaches adulthood. As demonstrated by this boy’s complicated course, practical multi-system guidelines are needed to assist the general practitioner and specialists in caring for patients with 22q11DS. Although still under-recognized, detection, including in the prenatal setting, is increasing. Moreover, the phenotypic spectrum is highly variable, and patients may present at any age. Thus, initial guidelines developed by an international panel of experts present the best practice recommendations currently available across the lifespan, with a major focus on the changing issues through childhood development.

Mutations in a new gene in Ellis-van Creveld syndrome and Weyers acrodental dysostosis

Ellis-van Creveld syndrome (EvC, MIM 225500) is an autosomal recessive skeletal dysplasia characterized by short limbs, short ribs, postaxial polydactyly and dysplastic nails and teeth. Congenital cardiac defects, most commonly a defect of primary atrial septation producing a common atrium, occur in 60% of affected individuals. The disease was mapped to chromosome 4p16 in nine Amish subpedigrees and single pedigrees from Mexico, Ecuador and Brazil. Weyers acrodental dysostosis (MIM 193530), an autosomal dominant disorder with a similar but milder phenotype, has been mapped in a single pedigree to an area including the EvC critical region. We have identified a new gene (EVC), encoding a 992–amino-acid protein, that is mutated in individuals with EvC. We identified a splice-donor change in an Amish pedigree and six truncating mutations and a single amino acid deletion in seven pedigrees. The heterozygous carriers of these mutations did not manifest features of EvC. We found two heterozygous missense mutations associated with a phenotype, one in a man with Weyers acrodental dysostosis and another in a father and his daughter, who both have the heart defect characteristic of EvC and polydactyly, but not short stature. We suggest that EvC and Weyers acrodental dysostosis are allelic conditions.

Isotopic evidence for neogene hominid paleoenvironments in the Kenya Rift Valley

Bipedality, the definitive characteristic of the earliest hominids, has been regarded as an adaptive response to a transition from forested to more-open habitats in East Africa sometime between 12 million and 5 million years ago. Analyses of the stable carbon isotopic composition (δ13C) of paleosol carbonate and organic matter from the Tugen Hills succession in Kenya indicate that a heterogeneous environment with a mix of C3 and C4 plants has persisted for the last 15.5 million years. Open grasslands at no time dominated this portion of the rift valley. The observed δ13C values offer no evidence for a shift from more-closed C3 environments to C4 grassland habitats. If hominids evolved in East Africa during the Late Miocene, they did so in an ecologically diverse setting.

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.

Congenital heart diseases in children with Noonan syndrome : An expanded cardiac spectrum with high prevalence of atrioventricular canal

OBJECTIVE To report the relative prevalence of various forms of congenital heart disease (CHD) in children with Noonan syndrome (NS) and to describe anatomic characteristics of the subgroup of patients with atrioventricular canal (AVC). STUDY DESIGN Phenotypic and cardiologic examinations were performed in 136 patients with NS and CHD evaluated at our hospital from January 1986 to December 1998. Cardiac evaluation included chest x-ray film, electrocardiogram, 2-dimensional and color Doppler echocardiography, cardiac catheterization with angiocardiography, and cardiac surgery. RESULTS The CHDs classically reported in NS, including pulmonary stenosis (39%), hypertrophic cardiomyopathy (10%), atrial septal defect (8%), and tetralogy of Fallot (4%), are well represented in our series; however, aortic coarctation (9%) and anomalies of the mitral valve (6%) may also occur in this syndrome. Moreover, AVC was diagnosed in 21 patients, representing 15% of all CHDs in our series. All patients showed a partial form of AVC, and an associated subaortic stenosis caused by additional anomalies of the mitral valve was detected in 5 of 21 (23.8%) of those patients. CONCLUSION Left-sided lesions, such as aortic coarctation and anomalies of the mitral valve, are not rare in patients with NS and CHD. Moreover, in this syndrome AVC is quite frequent, the partial form is prevalent, and subaortic stenosis caused by additional anomalies of the mitral valve may be present. This information should be taken into consideration during the cardiologic evaluation of children with NS.

Correlation between PTPN11 gene mutations and congenital heart defects in Noonan and LEOPARD syndromes

Noonan syndrome (MIM 163950), an autosomal dominant disorder with an estimated prevalence of 1/1000–2500 at birth, is characterised by short stature, facial anomalies, pterygium colli, and congenital heart disease.1,2 Although pulmonary valve stenosis with dysplastic leaflets, hypertrophic cardiomyopathy, and atrial septal defects (ASD) are the most common congenital heart defects in Noonan syndrome,3 a broad spectrum of cardiac phenotypes has been recognised.2–6 About half the affected individuals have PTPN11 gene mutations.7–9 This gene, which maps to chromosome 12q22-qter,10 encodes for the human SH2 domain containing protein tyrosine phosphatase (SHP2).11 PTPN11 gene mutations have also been detected in multiple lentigines/LEOPARD syndrome (multiple lentigines, ECG conduction abnormalities, ocular hypertelorism, pulmonary stenosis, abnormal genitalia, retardation of growth and sensorineural deafness; ML/LS, MIM 151100),12,13 in Noonan-like/multiple giant cell lesion syndrome (MIM 163955),8 in two families presumably affected by cardio-facio-cutaneous syndrome (CFCS, MIM 115150),14 but not in sporadic CFCS.15 The clinical and genetic heterogeneity of these disorders suggests a possible relation between different PTPN11 gene mutations and distinct clinical features. A genotype–phenotype correlation study in Noonan syndrome found an association between pulmonary stenosis and PTPN11 mutations.8 Our aim in this study was to screen a large cohort of patients with Noonan syndrome and ML/LS in order to expand the genotype–phenotype correlation analysis, with particular emphasis on cardiac diseases. ### Key points