Ruth Day

Whole-Exome-Sequencing Identifies Mutations in Histone Acetyltransferase Gene KAT6B in Individuals with the Say-Barber-Biesecker Variant of Ohdo Syndrome

Say-Barber-Biesecker-Young-Simpson syndrome (SBBYSS or Ohdo syndrome) is a multiple anomaly syndrome characterized by severe intellectual disability, blepharophimosis, and a mask-like facial appearance. A number of individuals with SBBYSS also have thyroid abnormalities and cleft palate. The condition usually occurs sporadically and is therefore presumed to be due in most cases to new dominant mutations. In individuals with SBBYSS, a whole-exome sequencing approach was used to demonstrate de novo protein-truncating mutations in the highly conserved histone acetyltransferase gene KAT6B (MYST4/MORF)) in three out of four individuals sequenced. Sanger sequencing was used to confirm truncating mutations of KAT6B, clustering in the final exon of the gene in all four individuals and in a further nine persons with typical SBBYSS. Where parental samples were available, the mutations were shown to have occurred de novo. During mammalian development KAT6B is upregulated specifically in the developing central nervous system, facial structures, and limb buds. The phenotypic features seen in the Qkf mouse, a hypomorphic Kat6b mutant, include small eyes, ventrally placed ears and long first digits that mirror the human phenotype. This is a further example of how perturbation of a protein involved in chromatin modification might give rise to a multisystem developmental disorder.

Molecular Analysis Expands the Spectrum of Phenotypes Associated with GLI3 Mutations

A range of phenotypes including Greig cephalopolysyndactyly and Pallister‐Hall syndromes (GCPS, PHS) are caused by pathogenic mutation of the GLI3 gene. To characterize the clinical variability of GLI3 mutations, we present a subset of a cohort of 174 probands referred for GLI3 analysis. Eighty‐one probands with typical GCPS or PHS were previously reported, and we report the remaining 93 probands here. This includes 19 probands (12 mutations) who fulfilled clinical criteria for GCPS or PHS, 48 probands (16 mutations) with features of GCPS or PHS but who did not meet the clinical criteria (sub‐GCPS and sub‐PHS), 21 probands (6 mutations) with features of PHS or GCPS and oral‐facial‐digital syndrome, and 5 probands (1 mutation) with nonsyndromic polydactyly. These data support previously identified genotype–phenotype correlations and demonstrate a more variable degree of severity than previously recognized. The finding of GLI3 mutations in patients with features of oral–facial–digital syndrome supports the observation that GLI3 interacts with cilia. We conclude that the phenotypic spectrum of GLI3 mutations is broader than that encompassed by the clinical diagnostic criteria, but the genotype–phenotype correlation persists. Individuals with features of either GCPS or PHS should be screened for mutations in GLI3 even if they do not fulfill clinical criteria. Hum Mutat 31:1142–1154, 2010.

Genotype-phenotype analysis in congenital adrenal hyperplasia due to P450 oxidoreductase deficiency

Context: P450 oxidoreductase deficiency (PORD) is a unique congenital adrenal hyperplasia variant that manifests with glucocorticoid deficiency, disordered sex development (DSD), and skeletal malformations. No comprehensive data on genotype-phenotype correlations in Caucasian patients are available. Objective: The objective of the study was to establish genotype-phenotype correlations in a large PORD cohort. Design: The design of the study was the clinical, biochemical, and genetic assessment including multiplex ligation-dependent probe amplification (MLPA) in 30 PORD patients from 11 countries. Results: We identified 23 P450 oxidoreductase (POR) mutations (14 novel) including an exonic deletion and a partial duplication detected by MLPA. Only 22% of unrelated patients carried homozygous POR mutations. p.A287P was the most common mutation (43% of unrelated alleles); no other hot spot was identified. Urinary steroid profiling showed characteristic PORD metabolomes with variable impairment of 17α-hydroxylase and 21-hydroxylase. Short cosyntropin testing revealed adrenal insufficiency in 89%. DSD was present in 15 of 18 46,XX and seven of 12 46,XY individuals. Homozygosity for p.A287P was invariably associated with 46,XX DSD but normal genitalia in 46,XY individuals. The majority of patients with mild to moderate skeletal malformations, assessed by a novel scoring system, were compound heterozygous for missense mutations, whereas nearly all patients with severe malformations carried a major loss-of-function defect on one of the affected alleles. Conclusions: We report clinical, biochemical, and genetic findings in a large PORD cohort and show that MLPA is a useful addition to POR mutation analysis. Homozygosity for the most frequent mutation in Caucasians, p.A287P, allows for prediction of genital phenotype and moderate malformations. Adrenal insufficiency is frequent, easily overlooked, but readily detected by cosyntropin testing.

Further delineation of the KAT6B molecular and phenotypic spectrum

KAT6B sequence variants have been identified previously in both patients with the Say-Barber-Biesecker type of blepharophimosis mental retardation syndromes (SBBS) and in the more severe genitopatellar syndrome (GPS). We report on the findings in a previously unreported group of 57 individuals with suggestive features of SBBS or GPS. Likely causative variants have been identified in 34/57 patients and were commonly located in the terminal exons of KAT6B. Of those where parental samples could be tested, all occurred de novo. Thirty out of thirty-four had truncating variants, one had a missense variant and the remaining three had the same synonymous change predicted to affect splicing. Variants in GPS tended to occur more proximally to those in SBBS patients, and genotype/phenotype analysis demonstrated significant clinical overlap between SBBS and GPS. The de novo synonymous change seen in three patients with features of SBBS occurred more proximally in exon 16. Statistical analysis of clinical features demonstrated that KAT6B variant-positive patients were more likely to display hypotonia, feeding difficulties, long thumbs/great toes and dental, thyroid and patella abnormalities than KAT6B variant-negative patients. The few reported patients with KAT6B haploinsufficiency had a much milder phenotype, though with some features overlapping those of SBBS. We report the findings in a previously unreported patient with a deletion of the KAT6B gene to further delineate the haploinsufficiency phenotype. The molecular mechanisms giving rise to the SBBS and GPS phenotypes are discussed.

A clinical and genetic study of the Say/Barber/Biesecker/Young-Simpson type of Ohdo syndrome

We report a series of eight patients with the Say/Barber/Biesecker/Young‐Simpson (SBBYS) type of Ohdo syndrome, which is the largest cohort described to date. We expand on the type, frequency and severity of the clinical characteristics in this condition; comment on the natural history of Ohdo syndrome and further refine previously published diagnostic criteria. Cytogenetic investigations and microarray CGH analysis undertaken in this cohort of patients failed to identify a chromosomal aetiology. It remains possible that this rare condition is heterogeneous and therefore caution must be undertaken during counselling until the underlying genetic mechanism(s) is (are) identified.

Index finger abnormalities in Simpson-Golabi-Behmel syndrome.

Simpson–Golabi–Behmel syndrome (SGBS) is an X linked recessive overgrowth disorder in which digital abnormalities are a well-described aspect of the phenotype. We report a case with marked index finger hypoplasia and a congenital abnormality of the proximal phalanx and review the literature detailing index finger abnormalities in this condition.

DYSCERNE - A European network of centres of expertise for dysmorphology

There are over 2,500 identifiable dysmorphic conditions, which individually are rare but together form a significant proportion of referrals to a genetic service. The rarity of these diseases means that even in Centres of Expertise established in many EU countries, experience can be limited, resulting in delay or uncertainty of diagnosis. To improve diagnosis of dysmorphic syndromes across the EU, a formal European Network for Dysmorphology was created within the EU-funded DYSCERNE project (2007-2010) coordinated by the UK (University of Manchester). It links a total of 85 centres, including 32 centres of expertise with the remaining centres acting as case submission nodes for a web-based electronic Dysmorphology Diagnostic System (DDS). Making a correct diagnosis is essential for patient management and for providing accurate information and counselling. The DDS allows rapid access for clinicians from across Europe to expert opinions increasing accuracy of diagnosis. It will also facilitate definition and classification of rare dysmorphic disorders and promote further research. Linked to DDS, educational tools in a modern, on-line format were created aimed to guide and educate clinicians throughout Europe on key aspects of clinical dysmorphology (http://www.dyscerne.org). One of the principal activities of the DYSCERNE network was developing best practice management guidelines which use a robust methodology. Management protocols for four selected conditions: Angelman, Noonan, Kabuki and Williams Syndromes will be available on the DYSCERNE website soon. There is a need to continue activities initiated by DYSCERNE, in particular to sustain European networking, which helps to make a correct diagnosis and continue development of management guidelines for further rare diseases. DYSCERNE is funded by the European Commission Public Health Executive Agency (DG Sanco) Project 2006122 - A European Network of Centres of Expertise for Dysmorphology, and is supported by the Manchester Academic Health Sciences Centre (MAHSC) and the NIHR Biomedical Research Centre.

DYSCERNE: developing clinical management guidelines for selected dysmorphic syndromes

The DYSCERNE Network of Centres of Expertise for dysmorphology (http://www.dyscerne.org), is developing clinical management guidelines for Williams (WS), Angelman (AS), Noonan (NS) and Kabuki (KS) syndromes. An initial scoping exercise identified these conditions as rare, complex, multi-system disorders, for which it was felt that affected patients, families and health/social care professionals would benefit from access to up-to-date evidence based management guidelines. Published evidence from which to develop management recommendations for these conditions is very limited, and devising a systematic and robust methodology has been challenging. Our approach is based on the Scottish Intercollegiate Guidelines Network (SIGN) method, which we modified placing more emphasis on expert opinion and consensus, whilst maintaining systematic rigour and transparency of processes. The development process includes: - Identification of key management issues by guideline group leaders. - Targeted, systematic literature searches using PubMed. - Review, identification and grading of results by panel of invited experts. - Consensus meetings at which experts present, discuss and agree recommendations. - Initial drafting of guideline document which is circulated amongst experts and stakeholders for comments. - Amendments incorporated and guidelines finalised. - Guidelines piloted and evaluated. - International dissemination. The process has involved 49 experts from 8 countries reviewing between them, over 1000 papers. The WS guidelines are currently being piloted in 20 centres, by paediatricians and geneticists. The first draft of AS guidelines has been circulated for feedback. Consensus meetings for NS and KS will be held very shortly. The finished guidelines will be available from the DYSCERNE website.

Skeletal manifestations in Ohdo syndrome: a case with bilateral patella dislocations.

We report a new case of Ohdo syndrome with bilateral patella dislocations where surgical intervention has been indicated. A review of the skeletal manifestations reported in the literature on Ohdo syndrome reveals that joint laxity and skeletal deformities are important aspects of the phenotype.

Examination of a fetus with congenital abnormality: a web tool designed by DYSCERNE--a network of centres of expertise for dysmorphology (www.dyscerne.org).

Dyscerne has designed a succinct and easy to use educational tool on examination of a fetus with congenital abnormality and/or dysmorphic features. Access to this power point presentation can be requested through the Dyscerne website (www.dyscerne.org). It has been developed for use by multiple specialties including clinical genetics, pathology, obstetrics, paediatrics, radiology. It provides a useful overview of fetal examination and takes only 15 min to work through. It is clearly laid out, subdivided into the practicalities of the examination, appropriate investigations, the diagnostic process, and follow-up for the family. It provides step-by-step advice on carrying out the examination, taking clinical measurements and photographs with links to more detailed notes such as how to perform a skin biopsy. The direct links are easy to use and include printable proformas and check lists for the clinical history and examination as well as all the relevant fetal growth charts. Figure 1 details the contents page of this educational tool and Fig. 2 shows example proformas.