Primary microcephaly (PM) is characterized by a small head since birth and is vastly heterogeneous both genetically and phenotypically. While most cases are monogenic, genetic interactions between ...Aspm and Wdr62 have recently been described in a mouse model of PM. Here, we used two complementary, holistic in vivo approaches: high throughput DNA sequencing of multiple PM genes in human patients with PM, and genome‐edited zebrafish modeling for the digenic inheritance of PM. Exomes of patients with PM showed a significant burden of variants in 75 PM genes, that persisted after removing monogenic causes of PM (e.g., biallelic pathogenic variants in CEP152). This observation was replicated in an independent cohort of patients with PM, where a PM gene panel showed in addition that the burden was carried by six centrosomal genes. Allelic frequencies were consistent with digenic inheritance. In zebrafish, non‐centrosomal gene casc5 −/− produced a severe PM phenotype, that was not modified by centrosomal genes aspm or wdr62 invalidation. A digenic, quadriallelic PM phenotype was produced by aspm and wdr62. Our observations provide strong evidence for digenic inheritance of human PM, involving centrosomal genes. Absence of genetic interaction between casc5 and aspm or wdr62 further delineates centrosomal and non‐centrosomal pathways in PM.
In a cohort of patients with primary microcephaly (PM), exome sequencing showed a significant burden of variants in PM genes, that persisted after removing monogenic causes of PM. The finding was confirmed in a replication cohort (not shown), and candidate centrosomal gene pairs were identified. Zebrafish genome editing produced a severe PM phenotype in casc5 −/− and no phenotype in aspm −/− or wdr62 −/− fishes. Zebrafish crosses displayed digenic interactions between centrosomal genes aspm and wdr62, and no interactions between non‐centrosomal gene casc5 and either aspm or wdr62, delineating centrosomal and non‐centrosomal pathways in PM. *p = .028.
Next-generation sequencing (NGS) has enabled new approaches for detection of mutations in the BRCA1 and BRCA2 genes responsible for hereditary breast and ovarian cancer (HBOC). The search for ...germline mutations in the BRCA1 and BRCA2 genes is of importance with respect to oncogenetic and surgical (bilateral mastectomy, ovariectomy) counselling. Testing tumor material for BRCA mutations is of increasing importance for therapeutic decision making as the poly ADP ribose polymerase (PARP) inhibitor, olaparib, is now available to treat patients with specific forms of ovarian cancer and BRCA mutations. Molecular genetics laboratories should develop reliable and sensitive techniques for the complete analysis of the BRCA1 and BRCA2 genes. This is a challenge due to the size of the coding sequence of the BRCA1/2 genes, the absence of hot spot mutations, and particularly by the lower DNA quality obtained from Formalin-Fixed Paraffin-Embedded (FFPE) tissue. As a result, a number of analyses are uninterpretable and do not always provide a result to the clinician, limiting the optimal therapeutic management of patients. The availability of Fresh Frozen Tissue (FFT) for some laboratories and the excellent quality of the DNA extracted from it offers an alternative. For this reason, we evaluated Multiplicom's BRCA MASTR Dx assay on a set of 97 FFT derived DNA samples, in combination with the MID for Illumina MiSeq for BRCA1 and BRCA2 mutation detection. We obtained interpretable NGS results for all tested samples and showed > 99,7% sensitivity, specificity and accuracy.
Background
Primary microcephaly (PM) is defined as a significant reduction in occipitofrontal circumference (OFC) of prenatal onset. Clinical and genetic heterogeneity of PM represents a diagnostic ...challenge.
Methods
We performed detailed phenotypic and genomic analyses in a large cohort (n = 169) of patients referred for PM and could establish a molecular diagnosis in 38 patients.
Results
Pathogenic variants in ASPM and WDR62 were the most frequent causes in non‐consanguineous patients in our cohort. In consanguineous patients, microarray and targeted gene panel analyses reached a diagnostic yield of 67%, which contrasts with a much lower rate in non‐consanguineous patients (9%). Our series includes 11 novel pathogenic variants and we identify novel candidate genes including IGF2BP3 and DNAH2. We confirm the progression of microcephaly over time in affected children. Epilepsy was an important associated feature in our PM cohort, affecting 34% of patients with a molecular confirmation of the PM diagnosis, with various degrees of severity and seizure types.
Conclusion
Our findings will help to prioritize genomic investigations, accelerate molecular diagnoses, and improve the management of PM patients.
Phenotyping and genetic analyses in 169 probands referred for primary microcephaly produced a molecular diagnosis in 38, with ASPM and WDR62 most prevalent in non‐consanguineous patients, and a total diagnostics rate of 67% in consanguineous patients. Our series includes 11 novel pathogenic variants and reveals epilepsy as a more frequent feature than previously reported.
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