Craniosynostosis: another feature of the 22q11.2 deletion syndrome

Recent Advances in Craniosynostosis

Craniosynostosis is a pathologic craniofacial disorder and is defined as the premature fusion of one or more cranial (calvarial) sutures. Cranial sutures are fibrous joints consisting of nonossified mesenchymal cells that play an important role in the development of healthy craniofacial skeletons. Early fusion of these sutures results in incomplete brain development that may lead to complications of several severe medical conditions including seizures, brain damage, mental delay, complex deformities, strabismus, and visual and breathing problems. As a congenital disease, craniosynostosis has a heterogeneous origin that can be affected by genetic and epigenetic alterations, teratogens, and environmental factors and make the syndrome highly complex. To date, approximately 200 syndromes have been linked to craniosynostosis. In addition to being part of a syndrome, craniosynostosis can be nonsyndromic, formed without any additional anomalies. More than 50 nuclear genes that relate to craniosynostosis have been identified. Besides genetic factors, epigenetic factors like microRNAs and mechanical forces also play important roles in suture fusion. As craniosynostosis is a multifactorial disorder, evaluating the craniosynostosis syndrome requires and depends on all the information obtained from clinical findings, genetic analysis, epigenetic or environmental factors, or gene modulators. In this review, we will focus on embryologic and genetic studies, as well as epigenetic and environmental studies. We will discuss published studies and correlate the findings with unknown aspects of craniofacial disorders.

An update of ophthalmic management in craniosynostosis

Craniosynostosis has a varied clinical spectrum, ranging from isolated single suture involvement to multisutural fusions. Syndromic and nonsyndromic patients require orchestrated and multidisciplinary care from birth to adulthood. Advances in our understanding of craniosynostosis over the last quarter-century have resulted in more systematic management of the problems associated with the syndromic and nonsyndromic forms of this condition. This review provides an update on the genetic basis of, management of strabismus and oculoplastic manifestations in, and visual surveillance of patients with craniosynostosis.

22q and two: 22q11.2 deletion syndrome and coexisting conditions

22q11.2 deletion syndrome (DS) is the most frequent copy number variant (CNV) affecting ~1/1,000 fetuses and ~1/2,000-4,000 children, resulting in recognizable but variable findings across multiple organ systems. Patients with atypical features should prompt consideration of coexisting diagnoses due to additional genome-wide mutations, CNVs, or mutations/CNVs on the other allele, unmasking autosomal recessive conditions. Importantly, a dual diagnosis compounds symptoms and impacts management. We previously reported seven patients with 22q11.2DS and: SCID, Trisomy 8 mosaicism, Bernard-Soulier, and CEDNIK syndromes. Here we present six additional unreported patients with 22q11.2DS and concurrent diagnoses. Records on 1,422 patients with 22q11.2DS, identified via FISH, microarray, or MLPA, followed in our 22q and You Center at the Children's Hospital of Philadelphia (CHOP) were reviewed to identify a dual diagnosis. In addition to our seven previously reported cases, we identified an additional six with 22q11.2DS and another coexisting condition identified via: molecular/cytogenetic studies, newborn screening, coagulation factor studies, or enzyme testing; these include CHARGE syndrome (CHD7 mutation), cystic fibrosis, a maternally inherited 17q12 deletion, G6PD deficiency, von Willebrand disease, and 1q21.1 deletion, resulting in an incidence of dual diagnoses at our center of 0.9%. The range of dual diagnoses identified in our cohort is notable, medically actionable, and may alter long-term outcome and recurrence risk counseling. Thus, our findings may support testing patients with 22q11.2DS using a combination of microarray, mutational analysis of the other allele/WES, to ensure appropriate personalized care, as formulating medical management decisions hinges on establishing the correct diagnoses in their entirety.

Genetic advances in craniosynostosis

Craniosynostosis, the premature ossification of one or more skull sutures, is a clinically and genetically heterogeneous congenital anomaly affecting approximately one in 2,500 live births. In most cases, it occurs as an isolated congenital anomaly, that is, nonsyndromic craniosynostosis (NCS), the genetic, and environmental causes of which remain largely unknown. Recent data suggest that, at least some of the midline NCS cases may be explained by two loci inheritance. In approximately 25-30% of patients, craniosynostosis presents as a feature of a genetic syndrome due to chromosomal defects or mutations in genes within interconnected signaling pathways. The aim of this review is to provide a detailed and comprehensive update on the genetic and environmental factors associated with NCS, integrating the scientific findings achieved during the last decade. Focus on the neurodevelopmental, imaging, and treatment aspects of NCS is also provided.

Developmental trajectories in 22q11.2 deletion

Chromosome 22q11.2 deletion syndrome (22q11.2DS), a neurogenetic condition, is the most common microdeletion syndrome affecting 1 in 2,000-4,000 live births and involving haploinsufficiency of ∼50 genes resulting in a multisystem disorder. Phenotypic expression is highly variable and ranges from severe life-threatening conditions to only a few associated features. Most common medical problems include: congenital heart disease, in particular conotruncal anomalies; palatal abnormalities, most frequently velopharyngeal incompetence (VPI); immunodeficiency; hypocalcemia due to hypoparathyroidism; genitourinary anomalies; severe feeding/gastrointestinal differences; and subtle dysmorphic facial features. The neurocognitive profile is also highly variable, both between individuals and during the course of development. From infancy onward, motor delays (often with hypotonia) and speech/language deficits are commonly observed. During the preschool and primary school ages, learning difficulties are very common. The majority of patients with 22q11.2DS have an intellectual level that falls in the borderline range (IQ 70-84), and about one-third have mild to moderate intellectual disability. More severe levels of intellectual disability are uncommon in children and adolescents but are more frequent in adults. Individuals with 22q11.2DS are at an increased risk for developing several psychiatric disorders including attention deficit with hyperactivity disorder (ADHD), autism spectrum disorder (ASD), anxiety and mood disorders, and psychotic disorders and schizophrenia. In this review, we will focus on the developmental phenotypic transitions regarding cognitive development in 22q11.2DS from early preschool to adulthood, and on the changing behavioral/psychiatric phenotype across age, on a background of frequently complex medical conditions.

[Clinical and genetic characteristics of craniosynostosis]

Craniosynostosis is caused by premature fusion of one or more cranial sutures leading to deformity of the cranium. Depending on the type and number of the sutures involved and the order of their fusion, different forms of deformities may develop. Two main types of craniosynostosis can be distinguished: non-syndromic (isolated) and syndromic forms. In the latter group the cranial deformity is usually associated with dysmorphic features, limb anomalies and other symptoms while in non-syndromic form the cranial deformity can be seen only. The type and severity of associated anomalies in the syndromic form are different. Early fusion of sutures can be caused by both environmental and genetic factors. In the present paper the authors aim to review the clinical features and genetic background of craniosynostosis focusing on some common syndromes.

Genome-wide copy number variation analysis of a Branchio-oto-renal syndrome cohort identifies a recombination hotspot and implicates new candidate genes

Branchio-oto-renal (BOR) syndrome is an autosomal dominant disorder characterized by branchial arch anomalies, hearing loss and renal dysmorphology. Although haploinsufficiency of EYA1 and SIX1 are known to cause BOR, copy number variation analysis has only been performed on a limited number of BOR patients. In this study, we used high-resolution array-based comparative genomic hybridization on 32 BOR probands negative for coding-sequence and splice-site mutations in known BOR-causing genes to identify potential disease-causing genomic rearrangements. Of the >1,000 rare and novel copy number variants we identified, four were heterozygous deletions of EYA1 and several downstream genes that had nearly identical breakpoints associated with retroviral sequence blocks, suggesting that non-allelic homologous recombination seeded by this recombination hotspot is important in the pathogenesis of BOR. A different heterozygous deletion removing the last exon of EYA1 was identified in an additional proband. Thus, in total five probands (14 %) had deletions of all or part of EYA1. Using a novel disease-gene prioritization strategy that includes network analysis of genes associated with other deletions suggests that SHARPIN (Sipl1), FGF3 and the HOXA gene cluster may contribute to the pathogenesis of BOR.

Craniosynostosis and radial ray defect: a rare presentation of 22q11.2 deletion syndrome

A newborn with bilateral coronal craniosynostosis, hypoplastic thumbs, imperforate anus, and prenatal growth restriction was evaluated and given the clinical diagnosis of Baller-Gerold syndrome (BGS). While confirmatory testing of RECQL4 was pending, the infant developed unexplained hypocalcemia, prompting testing for a 22q11.2 deletion. Subsequently, the infant was found to have a 22q11.2 deletion, and was negative for an RECQL4 mutation. We therefore conclude that 22q11.2 deletion syndrome can present with findings resembling the BGS phenotype.

Severe craniosynostosis in an infant with deletion 22q11.2 syndrome

We report a male infant with 22q11.2 deletion syndrome and very severe multi-sutural craniosynostosis associated with increased intracranial pressure, marked displacement of brain structures, and extensive erosion of the skull. While uni- or bi-sultural craniosynostosis is a recognized (though relatively uncommon) feature of 22q11 deletion syndrome, a severe multi-sutural presentation of this nature has never been reported. SNP Microarray was otherwise normal and the patient did not have common mutations in FGFR2, FGFR3, or TWIST associated with craniosynostosis. While markedly variable expressivity is an acknowledged feature of deletion 22q11 syndrome, herein we also consider and discuss the possibility that this infant may have been additionally affected with an undiagnosed single gene disorder.

Genetic basis of single-suture synostoses: genes, chromosomes and clinical implications

BACKGROUND

Non syndromic craniosynostoses are the most frequent craniofacial malformations worldwide. They represent a wide and heterogeneous group of entities, in which the dysmorphism may occur in a single (simple forms) or in multiple sutures (complex forms). Simple forms present a higher birth prevalence and are classified according to the involved suture and to the corresponding abnormal cranial shape: scaphocephaly (SC; sagittal suture), trigonocephaly (TC; metopic suture), anterior plagiocephaly (unilateral coronal suture), posterior plagiocephaly (unilateral lambdoid suture). They occur commonly as sporadic forms, although a familiar recurrence is sometimes observed, suggesting a mendelian inheritance. The genetic causes of simple craniosynostosis are still largely unknown, as mutations in common craniosynostosis-associated genes and structural chromosomal aberrations have been rarely found in these cases.

AIMS

This review is intended to dissect comprehensively the state-of-the art on the genetic etiology of single suture craniosynostoses, in the attempt to categorize all known disease-associated genes and chromosomal aberrations. Possible genotype/phenotype correlations are discussed as useful clues towards the definition of optimized clinical management flowcharts.

Syndrome-specific growth charts for 22q11.2 deletion syndrome in Caucasian children

Growth faltering occurs frequently in infancy in the 22q11 Deletion syndrome (22q11 DS). The subsequent course of growth in childhood and outcome for final adult height lacks consensus. We analyzed 5,149 growth data points from 812 Caucasian subjects with 22q11 DS, from neonates to 37 years old. Charts were constructed for height, weight, body mass index, and head circumference (OFC) using the LMS Chart Maker program. These charts were compared with the WHO birth to 4 years growth standard and US CDC 2000 growth reference between 5 and 20 years. Starting from the 50th centile at birth, by 6-9 months of age boys mean height and weight had fallen to the 9th centile, as did girls height but their weight fell less markedly, to the 25th centile. Feeding difficulties were non-contributory. In children under 2 years old with congenital heart disease (CHD) mean weight was -0.5 SD lighter than no CHD. Catch up growth occurred, more rapid in weight than height in boys. Up to 10 years old both sexes tracked between the 9th and 25th centiles. In adolescence, the trend was to overweight rather than obesity. At 19 years mean height was -0.72 SD for boys, -0.89 SD girls. OFC was significantly smaller than the WHO standard in infancy, between the 9th and 25th centile, rising to the 25th centile by 5 years old. Thereafter the mean was close to the 9th centile of the OFC UK growth reference, more prolonged and marked than in previous studies.

Genetic counseling for the 22q11.2 deletion

Because of advances in palliative medical care, children with the 22q11.2 deletion syndrome are surviving into adulthood. An increase in reproductive fitness will likely follow necessitating enhanced access to genetic counseling for these patients and their families. Primary care physicians/obstetric practitioners are in a unique position to identify previously undiagnosed patients as they reach reproductive age and to refer them for genetic counseling. To date, most deletions are de novo, secondary to homologous recombination between low-copy repeat sequences located within 22q11.2. Nonetheless, both somatic and germ line mosaicism has been observed giving unaffected parents a small risk of recurrence. Once present though there is a 50% chance for a person with this contiguous deletion to have an affected child. With this in mind, a variety of prenatal monitoring techniques, as well as, preimplantation genetic diagnosis are available depending on the specific level of risk.

Mosaic 22q11.2 microdeletion syndrome: diagnosis and clinical manifestations of two cases

Chromosome 22q11.2 microdeletion syndrome is due to microdeletion of 22q11.2 region of chromosome 22. It is a common microdeletion syndrome however mosaic cases are very rare and reported only few previous occasions. In this report we describe two unrelated male children with clinical features consistent with 22q11.2 microdeletion syndrome characterized by cardiac defect, facial dysmorphism and developmental deficiency. One of the cases also had trigonocephaly. Interphase & metaphase FISH with 22q11.2 probe demonstrated mosaicism for hemizygous deletion of 22q11.2 region. Mosaicism is also observed in buccal cells as well as urine cells. Parents were without any deletion. These two cases represent rare cases of mosaic 22q11.2 microdeletion syndrome.

Craniosynostosis associated with distal 5q-trisomy: further evidence that extra copy of MSX2 gene leads to craniosynostosis

Distal 5q-trisomy has been reported in less than 30 patients, with craniosynostosis present in five. We report two new patients with distal 5q-trisomy craniosynostosis. Patient 1 had mild Kleeblattschädel with synostosis of multiple sutures together with wide and medially deviated thumbs and halluces, indicative of Pfeiffer syndrome. Cytogenetic and CGH analyses showed a karyotype of 46,XY,der(10)t(5;10)(q33;q26.3). Patient 2 had a prominent forehead and ridging of the metopic suture. Craniosynostosis of the metopic suture was shown by CT scan. Cytogenetic and CGH analyses disclosed a karyotype of 46,XX,der(17)t(5;17)(q35.1;p13.3). Of the 22 previously reported patients, all had microcephaly and 14 had an abnormal skull shape. Our results support the previous finding that distal 5q-trisomy together with an extra copy of the MSX2 gene leads to abnormal closure of sutures and craniosynostosis.

Trigonocephaly in a boy with paternally inherited deletion 22q11.2 syndrome

Deletion 22q11.2 syndrome is a well-known contiguous gene syndrome, for which the list of findings is extensive and varies from patient to patient. We encountered a unique patient who had a familial 3-Mb deletion 22q11.2 associated with trigonocephaly derived from craniosynostosis of the metopic suture. Almost all the symptoms of the patient, including polymicrogyria, microcephaly, facial abnormalities, internal anomalies, seizures, and mental retardation, were compatible with deletion 22q11.2 syndrome, except for synostosis of the metopic suture. This is the first report of a relationship between deletion 22q11.2 syndrome and trigonocephaly. Craniosynostosis of the metopic suture might be a minor complication of deletion 22q11.2, although coincidental occurrence cannot be ruled out.

Velo-cardio-facial syndrome: the pediatric otolaryngologist's perspective

PURPOSE OF REVIEW

The understanding of velo-cardio-facial syndrome has grown markedly since the initial descriptions of this common genetic disorder nearly 30 years ago. Our knowledge of the syndrome has advanced in part from opportunities to monitor many patients into adulthood because of advances in the fields of cardiothoracic surgery and immunology. Longitudinal study has brought to light psychiatric and behavioral features of the syndrome that are often not apparent until late adolescence or the early adult years. Certain endocrine and immunologic features of the syndrome thought to be resolved in childhood are now witnessed in older patients. Variable expression and lack of disease awareness are two major factors that contribute to the delays in diagnosis in many cases. To address this, there has been a call to delineate screening parameters for patients at risk of carrying the deletion.

RECENT FINDINGS

Several areas are highlighted in this review, reflecting the focus of scholarly work on velo-cardio-facial syndrome in the past year. Molecular genetics has shown smaller deletions in many families with the syndrome. The gene TBX1 has been found to be important to the phenotype. Surgical outcomes data reveal the greater challenges involved in correcting velopharyngeal insufficiency.

SUMMARY

Defining the genetic basis of velo-cardio-facial syndrome will allow clinicians and basic scientists to make further inroads into understanding the variable expressivity of this syndrome. It is also important to be aware of the continued diagnostic challenges encountered by clinicians in attempts to improve the detection of patients with this syndrome.