Alexander Hoischen

Background: There is tremendous potential for genome sequencing to improve clinical diagnosis and care once it becomes routinely accessible, but this will require formalizing research methods into clinical best practices in the areas of sequence data generation, analysis, interpretation and reporting. The CLARITY Challenge was designed to spur convergence in methods for diagnosing genetic disease starting from clinical case history and genome sequencing data. DNA samples were obtained from three families with heritable genetic disorders and genomic sequence data were donated by sequencing platform vendors. The challenge was to analyze and interpret these data with the goals of identifying disease-causing variants and reporting the findings in a clinically useful format. Participating contestant groups were solicited broadly, and an independent panel of judges evaluated their performance. Results: A total of 30 international groups were engaged. The entries reveal a general convergence of practices on most elements of the analysis and interpretation process. However, even given this commonality of approach, only two groups identified the consensus candidate variants in all disease cases, demonstrating a need for consistent fine-tuning of the generally accepted methods. There was greater diversity of the final clinical report content and in the patient consenting process, demonstrating that these areas require additional exploration and standardization. Conclusions: The CLARITY Challenge provides a comprehensive assessment of current practices for using genome sequencing to diagnose and report genetic diseases. There is remarkable convergence in bioinformatic techniques, but medical interpretation and reporting are areas that require further development by many groups.

Recently, pathogenic variants in the MLL2 gene were identified as the most common cause of Kabuki (Niikawa–Kuroki) syndrome (MIM#147920). To further elucidate the genotype–phenotype correlation, we studied a large cohort of 86 clinically defined patients with Kabuki syndrome (KS) for mutations in MLL2. All patients were assessed using a standardized phenotype list and all were scored using a newly developed clinical score list for KS (MLL2‐Kabuki score 0–10). Sequencing of the full coding region and intron–exon boundaries of MLL2 identified a total of 45 likely pathogenic mutations (52%): 31 nonsense, 10 missense and four splice‐site mutations, 34 of which were novel. In five additional patients, novel, i.e. non‐dbSNP132 variants of clinically unknown relevance, were identified. Patients with likely pathogenic nonsense or missense MLL2 mutations were usually more severely affected (median ‘MLL2‐Kabuki score’ of 6) as compared to the patients without MLL2 mutations (median ‘MLL2‐Kabuki score’ of 5), a significant difference (p < 0.0014). Several typical facial features such as large dysplastic ears, arched eyebrows with sparse lateral third, blue sclerae, a flat nasal tip with a broad nasal root, and a thin upper and a full lower lip were observed more often in mutation positive patients.

Floating-Harbor syndrome (FHS) is a rare condition characterized by short stature, delays in expressive language, and a distinctive facial appearance. Recently, heterozygous truncating mutations in SRCAP were determined to be disease-causing. With the availability of a DNA based confirmatory test, we set forth to define the clinical features of this syndrome. Clinical information on fifty-two individuals with SRCAP mutations was collected using standardized questionnaires. Twenty-four males and twenty-eight females were studied with ages ranging from 2 to 52 years. The facial phenotype and expressive language impairments were defining features within the group. Height measurements were typically between minus two and minus four standard deviations, with occipitofrontal circumferences usually within the average range. Thirty-three of the subjects (63%) had at least one major anomaly requiring medical intervention. We did not observe any specific phenotype-genotype correlations. This large cohort of individuals with molecularly confirmed FHS has allowed us to better delineate the clinical features of this rare but classic genetic syndrome, thereby facilitating the development of management protocols.

Zusammenfassung: Neueste Sequenziertechnologien („next-generation sequencing“) erlauben die gleichzeitige Sequenzierung aller proteinkodierender Sequenzen, das sog. Exom. Die Identifizierung der jeweiligen pathogenen Mutation unter den Tausenden detektierten Varianten stellt dabei eine große Herausforderung dar, und neue Strategien für die Priorisierung von Varianten sind unerlässlich. Die jeweilige Wahl einer Strategie ist dabei von verschiedenen Faktoren abhängig, wie z. B. dem Vorhandensein gut charakterisierter Patienten und deren Familien, von der Art der Vererbung, der Schwere der Krankheit sowie deren Frequenz in der allgemeinen Bevölkerung. In dem vorliegenden Übersichtsartikel diskutieren wir die heute gebräuchlichen Strategien zur Identifizierung von neuen Krankheitsgenen mittels Exom-Sequenzierung und beschreiben die Lehren der ersten Exom-Studien. Wir glauben, dass die Sequenzierung von Exomen in den folgenden Jahren die am häufigsten angewandte Methode zur Identifizierung von Krankheitsgenen sein wird und dabei gleichzeitig auch ein großes diagnostisches Potenzial aufweist.