Anne-Karin Kahlert

Association Between Loss-of-Function Mutations Within the FANCM Gene and Early-Onset Familial Breast Cancer

Importance Germline mutations in established moderately or highly penetrant risk genes for breast cancer (BC) and/or ovarian cancer (OC), including BRCA1 and BRCA2, explain fewer than half of all familial BC and/or OC cases. Based on the genotyping of 2 loss-of-function (LoF) variants c.5101C>T (p.GIn1701Ter [rs147021911]) and c.5791C>T (p.Arg1931Ter [rs144567652]), the FANCM gene has been suggested as a novel BC predisposition gene, while the analysis of the entire coding region of the FANCM gene in familial index cases and geographically matched controls is pending. Objectives To assess the mutational spectrum within the FANCM gene, and to determine a potential association of LoF germline mutations within the FANCM gene with BC and/or OC risk. Design, Setting, and Participants For the purpose of identification and characterization of novel BC and/or OC predisposition genes, a total of 2047 well-characterized familial BC index cases, 628 OC cases, and 2187 geographically matched controls were screened for LoF mutations within the FANCM gene by next-generation sequencing. All patients previously tested negative for pathogenic BRCA1 and BRCA2 mutations. All data collection occurred between June 1, 2013, and April 30, 2016. Data analysis was performed from May 1, 2016, to July 1, 2016. Main Outcomes and Measures FANCM LoF mutation frequencies in patients with BC and/or OC were compared with the FANCM LoF mutation frequencies in geographically matched controls by univariate logistic regression. Positive associations were stratified by age at onset and cancer family history. Results In this case-control study, 2047 well-characterized familial female BC index cases, 628 OC cases, and 2187 geographically matched controls were screened for truncating FANCM alterations. Heterozygous LoF mutations within the FANCM gene were significantly associated with familial BC risk, with an overall odds ratio (OR) of 2.05 (95% CI, 0.94-4.54; P = .049) and a mutation frequency of 1.03% in index cases. In familial patients whose BC onset was before age 51 years, an elevated OR of 2.44 (95% CI, 1.08-5.59; P = .02) was observed. A more pronounced association was identified for patients with a triple-negative BC tumor phenotype (OR, 3.75; 95% CI, 1.00-12.85; P = .02). No significant association was detected for unselected OC cases (OR, 1.74; 95% CI, 0.57-5.08; P = .27). Conclusions and Relevance Based on the significant associations of heterozygous LoF mutations with early-onset or triple-negative BC, FANCM should be included in diagnostic gene panel testing for individual risk assessment. Larger studies are required to determine age-dependent disease risks for BC and to assess a potential role of FANCM mutations in OC pathogenesis.

BRIP1 loss-of-function mutations confer high risk for familial ovarian cancer, but not familial breast cancer

BackgroundGermline mutations in the BRIP1 gene have been described as conferring a moderate risk for ovarian cancer (OC), while the role of BRIP1 in breast cancer (BC) pathogenesis remains controversial.MethodsTo assess the role of deleterious BRIP1 germline mutations in BC/OC predisposition, 6341 well-characterized index patients with BC, 706 index patients with OC, and 2189 geographically matched female controls were screened for loss-of-function (LoF) mutations and potentially damaging missense variants. All index patients met the inclusion criteria of the German Consortium for Hereditary Breast and Ovarian Cancer for germline testing and tested negative for pathogenic BRCA1/2 variants.ResultsBRIP1 LoF mutations confer a high OC risk in familial index patients (odds ratio (OR) = 20.97, 95% confidence interval (CI) = 12.02–36.57, P < 0.0001) and in the subgroup of index patients with late-onset OC (OR = 29.91, 95% CI = 14.99–59.66, P < 0.0001). No significant association of BRIP1 LoF mutations with familial BC was observed (OR = 1.81 95% CI = 1.00–3.30, P = 0.0623). In the subgroup of familial BC index patients without a family history of OC there was also no apparent association (OR = 1.42, 95% CI = 0.70–2.90, P = 0.3030). In 1027 familial BC index patients with a family history of OC, the BRIP1 mutation prevalence was significantly higher than that observed in controls (OR = 3.59, 95% CI = 1.43–9.01; P = 0.0168). Based on the negative association between BRIP1 LoF mutations and familial BC in the absence of an OC family history, we conclude that the elevated mutation prevalence in the latter cohort was driven by the occurrence of OC in these families. Compared with controls, predicted damaging rare missense variants were significantly more prevalent in OC (P = 0.0014) but not in BC (P = 0.0693) patients.ConclusionsTo avoid ambiguous results, studies aimed at assessing the impact of candidate predisposition gene mutations on BC risk might differentiate between BC index patients with an OC family history and those without. In familial cases, we suggest that BRIP1 is a high-risk gene for late-onset OC but not a BC predisposition gene, though minor effects cannot be excluded.

Pierpont syndrome: report of a new patient

Pierpont syndrome (OMIM #602342) is a rare disorder characterized by developmental delay, characteristic facial gestalt, hearing loss, and abnormal fat distribution in the distal limbs. A specific mutation in TBL1XR1 [c.1337A>G; p.(Tyr446Cys)] has been described recently in six unrelated patients with Pierpont syndrome. We report on a male child with developmental delay, distinctive facial dysmorphic features, dystrophy, and abnormal fat distribution in the feet, in whom we identified the identical TBL1XR1 mutation. This patient also had additional clinical features including microphthalmia, pendular nystagmus, cryptorchidism, dermal sinus, and peripheral joint laxity, which had not been reported previously in association with Pierpont syndrome. This patient corroborates the assumption that Pierpont syndrome is exclusively caused by the specific TBL1XR1 missense mutation p.(Tyr446Cys) and the additional features broaden the phenotypic spectrum of this rare disorder.

Novel PRPS1 gain‐of‐function mutation in a patient with congenital hyperuricemia and facial anomalies

Phosphoribosylpyrophosphate synthetase (PRPPS) superactivity (OMIM 300661) is a rare inborn error of purine metabolism that is caused by gain‐of‐function mutations in the X‐chromosomal gene PRPS1 (Xq22.3). Clinical characteristics include congenital hyperuricemia and hyperuricosuria, gouty arthritis, urolithiasis, developmental delay, hypotonia, recurrent infections, short stature, and hearing loss. Only eight families with PRPPS superactivity and PRPS1 gain‐of‐function mutations have been reported to date. We report on a 7‐year‐old boy with congenital hyperuricemia, urolithiasis, developmental delay, short stature, hypospadias, and facial dysmorphisms. His mother also suffered from hyperuricemia that was diagnosed at age 13 years. A novel PRPS1 missense mutation (c.573G>C, p.[Leu191Phe]) was detected in the proband and his mother. Enzyme activity analysis confirmed superactivity of PRPP synthetase. Analysis of the crystal structure of human PRPPS suggests that the Leu191Phe mutation affects the architecture of both allosteric sites, thereby preventing the allosteric inhibition of the enzyme. The family reported here broadens the clinical spectrum of PRPPS superactivity and indicates that this rare metabolic disorder might be associated with a recognizable facial gestalt.

Diagnostic value of partial exome sequencing in developmental disorders

Although intellectual disability is one of the major indications for genetic counselling, there are no homogenous diagnostic algorithms for molecular testing. While whole exome sequencing is increasingly applied, we questioned whether analyzing a partial exome, enriched for genes associated with Mendelian disorders, might be a valid alternative approach that yields similar detection rates but requires less sequencing capacities. Within this context 106 patients with different intellectual disability forms were analyzed for mutations in 4.813 genes after pre-exclusion of copy number variations by array-CGH. Subsequent variant interpretation was performed in accordance with the ACMG guidelines. By this, a molecular diagnosis was established in 34% of cases and candidate mutations were identified in additional 24% of patients. Detection rates of causative mutations were above 30%, regardless of further symptoms, except for patients with seizures (23%). We did not detect an advantage from partial exome sequencing for patients with severe intellectual disability (36%) as compared to those with mild intellectual disability (44%). Specific clinical diagnoses pre-existed for 20 patients. Of these, 5 could be confirmed and an additional 6 cases could be solved, but showed mutations in other genes than initially suspected. In conclusion partial exome sequencing solved >30% of intellectual disability cases, which is similar to published rates obtained by whole exome sequencing. The approach therefore proved to be a valid alternative to whole exome sequencing for molecular diagnostics in this cohort. The method proved equally suitable for both syndromic and non-syndromic intellectual disability forms of all severity grades.

Genetik der angeborenen Herzfehler

ZusammenfassungStrukturelle Herzfehler sind eine der häufigsten menschlichen Fehlbildungen. Es lassen sich mehrere morphologische Gruppen unterscheiden, wobei auch Überlappungen mit verschiedenen Formen der Kardiomyopathien, unter anderem mit der Non-Compaction Kardiomyopathie, beobachtet werden. Zum jetzigen Zeitpunkt liegt nur ein sehr eingeschränktes Verständnis der zugrunde liegenden genetischen Ursachen vor. Dies liegt zum einen an einer „komplexen Genetik“, bei welcher häufig reduzierte Penetranz und variable Expressivität vorliegen, zum anderen aber auch an heterogenen Literaturangaben, bei denen nur unzureichende genetische Evidenzen bestehen. Der Fokus dieses Reviews ist es, anhand von stringenten Evidenzkriterien die bekannten Gene für strukturelle Herzfehler darzustellen. Speziell durch die Nutzung von Next Generation Sequencing (NGS) können zunehmend mehr relevante genetische Zusammenhänge geklärt werden. Dies gilt nicht nur für die Validierung von Genotyp-Phänotyp-Assoziationen, sondern auch für die Identifizierung neuer Gene für angeborene Herzfehler (AHF), was besonders wegen des seltenen Vorkommens rekurrenter AHF-assoziierter Mutationen im gleichen Gen in Zukunft notwendig sein wird. Um dieses Ziel zu erreichen, ist es notwendig, große deutschlandweite oder internationale Studien zu etablieren und bereits publizierte Datensätze öffentlich zugänglich zu machen. Dies sollte auch für diagnostische Datensätze gelten. Mit einem derartigen Ansatz könnte nicht nur eine Gen-Panel-Diagnostik, sondern auch die Eingruppierung der Herzfehler in therapeutische Subgruppen erreicht werden.AbstractCongenital heart disease (CHD) is the most common congenital malformation in humans. Morphologically, it is possible to distinguish different forms, some of which, such as non-compaction cardiomyopathy, show a significant overlap with cardiomyopathies. Currently, our understanding of the underlying genetics is limited, because of its complexity, in which reduced penetrance and variable expressivity are often observed. In addition, the available literature is often diverse, and consists of inadequate genetic evidence. Therefore, the focus of this review is to present the genes known to be involved in CHD, based on stringent criteria. With the use of next generation sequencing (NGS) technologies, an increasing number of relevant genetic connections can be clarified. It not only helps to establish strong genotype–phenotype associations, but also to identify novel CHD genes, which will be urgently needed in the future given the rare occurrence of recurrent CHD-associated mutations in the same gene. To achieve this goal, it will be necessary to establish nationwide and international studies and make published datasets available to the community. The same applies to diagnostic datasets. Such an approach would be helpful in obtaining gene panel diagnostics and in classifying CHD into therapeutic subgroups.