Cecilie F. Rustad

Primary immunodeficiency diseases: Genomic approaches delineate heterogeneous Mendelian disorders

Background: Primary immunodeficiency diseases (PIDDs) are clinically and genetically heterogeneous disorders thus far associated with mutations in more than 300 genes. The clinical phenotypes derived from distinct genotypes can overlap. Genetic etiology can be a prognostic indicator of disease severity and can influence treatment decisions. Objective: We sought to investigate the ability of whole‐exome screening methods to detect disease‐causing variants in patients with PIDDs. Methods: Patients with PIDDs from 278 families from 22 countries were investigated by using whole‐exome sequencing. Computational copy number variant (CNV) prediction pipelines and an exome‐tiling chromosomal microarray were also applied to identify intragenic CNVs. Analytic approaches initially focused on 475 known or candidate PIDD genes but were nonexclusive and further tailored based on clinical data, family history, and immunophenotyping. Results: A likely molecular diagnosis was achieved in 110 (40%) unrelated probands. Clinical diagnosis was revised in about half (60/110) and management was directly altered in nearly a quarter (26/110) of families based on molecular findings. Twelve PIDD‐causing CNVs were detected, including 7 smaller than 30 Kb that would not have been detected with conventional diagnostic CNV arrays. Conclusion: This high‐throughput genomic approach enabled detection of disease‐related variants in unexpected genes; permitted detection of low‐grade constitutional, somatic, and revertant mosaicism; and provided evidence of a mutational burden in mixed PIDD immunophenotypes.

Mutations in LZTR1 add to the complex heterogeneity of schwannomatosis

Objectives: We aimed to determine the proportion of individuals in our schwannomatosis cohort whose disease is associated with an LZTR1 mutation. Methods: We used exome sequencing, Sanger sequencing, and copy number analysis to screen 65 unrelated individuals with schwannomatosis who were negative for a germline NF2 or SMARCB1 mutation. We also screened samples from 39 patients with a unilateral vestibular schwannoma (UVS), plus at least one other schwannoma, but who did not have an identifiable germline or mosaic NF2 mutation. Results: We identified germline LZTR1 mutations in 6 of 16 patients (37.5%) with schwannomatosis who had at least one affected relative, 11 of 49 (22%) sporadic patients, and 2 of 39 patients with UVS in our cohort. Three germline mutation–positive patients in total had developed a UVS. Mosaicism was excluded in 3 patients without germline mutation in NF2, SMARCB1, or LZTR1 by mutation screening in 2 tumors from each. Conclusions: Our data confirm the relationship between mutations in LZTR1 and schwannomatosis. They indicate that germline mutations in LZTR1 confer an increased risk of vestibular schwannoma, providing further overlap with NF2, and that further causative genes for schwannomatosis remain to be identified.

Vestibular schwannomas occur in schwannomatosis and should not be considered an exclusion criterion for clinical diagnosis

Schwannomatosis is a recently delineated inherited condition that has clinical overlap with neurofibromatosis type 2 (NF2). Diagnostic criteria have been developed to distinguish schwannomatosis from NF2, but the existence of mosaic NF2, which may closely mimic schwannomatosis, makes even these criteria problematic. In particular, it is not clear why there is a relative sparing of the cranial nerves from schwannomas in schwannomatosis. We have identified two individuals with schwannomatosis and a unilateral vestibular schwannoma (VS), where a diagnosis of NF2 has been excluded. A third case with an identified SMARCB1 mutation was reported by two radiologists to have a VS, but this was later confirmed as a jugular schwannoma. These cases question whether the current exclusion of a VS from the clinical diagnosis of schwannomatosis is justified.

15q11.2 microdeletion – Seven new patients with delayed development and/or behavioural problems

15q11.2 microdeletion has been suggested as a new microdeletion syndrome and several patients have been described in the literature. We report seven new patients belonging to six families, age 9-24 years old, with a 350 kb 15q11.2 deletion of the four highly conserved genes (TUBGCP5, NIPA1, NIPA2 and CYFIP1) earlier reported. All our patients had some degree of learning difficulties, delayed development and/or behavioural problems. Common dysmorphic features and congenital malformations were not characteristics of our patients. The deletion was inherited from a mildly affected parent in all cases tested (5/6 families available for testing both parents). These seven new cases confirm some of the features earlier reported to be associated with 15q11.2 deletion, and help to further delineate the phenotype associated with 15q11.2 deletion.

The cardiac phenotype in patients with a CHD7 mutation

Background—Loss-of-function mutations in CHD7 cause Coloboma, Heart Disease, Atresia of Choanae, Retardation of Growth and/or Development, Genital Hypoplasia, and Ear Abnormalities With or Without Deafness (CHARGE) syndrome, a variable combination of multiple congenital malformations including heart defects. Heart defects are reported in 70% to 92% of patients with a CHD7 mutation, but most studies are small and do not provide a detailed classification of the defects. We present the first, detailed, descriptive study on the cardiac phenotype of 299 patients with a CHD7 mutation and discuss the role of CHD7 in cardiac development. Methods and Results—We collected information on congenital heart defects in 299 patients with a pathogenic CHD7 mutation, of whom 220 (74%) had a congenital heart defect. Detailed information on the heart defects was available for 202 of these patients. We classified the heart defects based on embryonic cardiac development and compared the distribution to 1007 equally classified nonsyndromic heart defects of patients registered by EUROCAT, a European Registry of Congenital Anomalies. Heart defects are highly variable in patients with CHD7 mutations, but atrioventricular septal defects and conotruncal heart defects are over-represented. Sex did not have an effect on the presence of heart defects, but truncating CHD7 mutations resulted in a heart defect significantly more often than missense or splice-site mutations (&khgr;2, P<0.001). Conclusions—CHD7 plays an important role in cardiac development, given that we found a wide range of heart defects in 74% of a large cohort of patients with a CHD7 mutation. Conotruncal defects and atrioventricular septal defects are over-represented in patients with CHD7 mutations compared with patients with nonsyndromic heart defects.

Growth in individuals with Majewski osteodysplastic primordial dwarfism type II caused by pericentrin mutations

Microcephalic primordial dwarfism (MPD) is a class of disorders characterized by intrauterine growth restriction (IUGR), impaired postnatal growth and microcephaly. Majewski osteodysplastic primordial dwarfism type II (MOPD II) is one of the more common conditions within this group. MOPD II is caused by truncating mutations in pericentrin (PCNT) and is inherited in an autosomal recessive manner. Detailed growth curves for length, weight, and OFC are presented here and derived from retrospective data from 26 individuals with MOPD II confirmed by molecular or functional studies. Severe pre‐ and postnatal growth failure is evident in MOPD II patients. The length, weight, and OFC at term (when corrected for gestational age) were −7.0, −3.9, and −4.6 standard deviation (SD) below the population mean and equivalent to the 50th centile of a 28–29‐, 31–32‐, and 30–31‐week neonate, respectively. While at skeletal maturity, the height, weight, and OFC were −10.3, −14.3, and −8.5 SD below the population mean and equivalent to the size of 3‐year 10‐ to 11‐month‐old, a 5‐year 2‐ to 3‐month‐old, and 5‐ to 6‐month‐old, respectively. During childhood, MOPD II patients grow with slowed, but fairly constant growth velocities and show no evidence of any pubertal growth spurt. Treatment with human growth hormone (n = 11) did not lead to any significant improvement in final stature. The growth charts presented here will be of assistance with diagnosis and management of MOPD II, and should have particular utility in nutritional management of MOPD II during infancy.

Characterization of a Norwegian cherubism cohort; molecular genetic findings, oral manifestations and quality of life.

Bilateral multilocular radiolucencies of the mandible are the main feature of cherubism (OMIM #118400), a rare autosomal dominant disorder primarily affecting the jaw. Typically, symmetrical swelling of the lower face is evident from around three years of age and increases until puberty. The underlying radiolucent lesions consist of vascular fibrotic stroma with scattered multinuclear giant cells. By age 30 years the facial contours are often unremarkable. Missing and displaced teeth as well as premature tooth loss are characteristic. Diagnosis rests upon a combination of clinical, radiographic, histological and molecular findings. SH3BP2 is currently the only gene known to be associated with cherubism. This cross-sectional study describes oral manifestations, quality of life and results of mutation analysis of SH3BP2 in 11 females and 13 males ages five to 84 years with cherubism. One individual with molecularly confirmed Noonan syndrome was excluded from the cohort. Standard statistical tools were used to analyze quality of life data. Mutation analysis was positive in all 22 familial and negative in both sporadic cases. Disease manifestations in mutation carriers varied from none to severe. Although intra-familial variability was marked, we found no evidence of non-penetrance, and females were on average more severely affected than males. Dental sequelae were pronounced; adults lacked a mean of 13 teeth (range 2-28), 13 of 17 individuals aged 16 years and older had removable or fixed dentures and five had dental implants; implant survival rate was 79%. In spite of pronounced disease manifestations and dental sequelae, adult quality of life was good.

Axial Spondylometaphyseal Dysplasia Is Caused by C21orf2 Mutations

Axial spondylometaphyseal dysplasia (axial SMD) is an autosomal recessive disease characterized by dysplasia of axial skeleton and retinal dystrophy. We conducted whole exome sequencing and identified C21orf2 (chromosome 21 open reading frame 2) as a disease gene for axial SMD. C21orf2 mutations have been recently found to cause isolated retinal degeneration and Jeune syndrome. We found a total of five biallelic C21orf2 mutations in six families out of nine: three missense and two splicing mutations in patients with various ethnic backgrounds. The pathogenic effects of the splicing (splice-site and branch-point) mutations were confirmed on RNA level, which showed complex patterns of abnormal splicing. C21orf2 mutations presented with a wide range of skeletal phenotypes, including cupped and flared anterior ends of ribs, lacy ilia and metaphyseal dysplasia of proximal femora. Analysis of patients without C21orf2 mutation indicated genetic heterogeneity of axial SMD. Functional data in chondrocyte suggest C21orf2 is implicated in cartilage differentiation. C21orf2 protein was localized to the connecting cilium of the cone and rod photoreceptors, confirming its significance in retinal function. Our study indicates that axial SMD is a member of a unique group of ciliopathy affecting skeleton and retina.

Neurofibromatosis type 2: Multiple intra-dermal tumors in a toddler

1Department of Medical Genetics, Oslo University Hospital Rikshospitalet, Oslo, Norway 2Department of Child Neurology, Oslo University Hospital Rikshospitalet, Nydalen, Oslo, Norway 3Manchester Centre for Genomic Medicine, St Marys Hospital, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK 4Department of Dermatology, Oslo University Hospital Rikshospitalet, Nydalen, Oslo, Norway 5Manchester Centre for Genomic Medicine, St Marys Hospital, Central Manchester University Hospitals NHS Foundation Trust, Manchester Academic Health Sciences Centre, Manchester, UK 6Department of Laboratory Medicine, Telemark Hospital, Ulefossveien, Skien, Norway 7University of Manchester, Division of Evolution and Genomic Science, St Marys Hospital, Manchester Academic Health Science Centre, Central Manchester Foundation Trust, Manchester, UK Correspondence Cecilie F. Rustad, Department of Medical Genetics, Oslo University Hospital, Po box 4950 Nydalen, 0424 Oslo, Norway. Email: cerus@ous-hf.no