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Current methods of next generation sequencing may simultaneously detect multiple germline breast cancer susceptibility variants. However, it is a challenge to maximize the clinical benefit of genetic analysis for patients and family members while minimizing potentially harmful effects. Relevant issues include criteria for referral, the choice of gene panel, handling of variants of unknown significance, cancer risk counselling in clinical context including family history data, risks of tumours other than breast cancer, handling of potential germline findings revealed by tumour testing and the clinical management of gene variant carriers, including surveillance, targeted therapy, radiotherapy and risk-reducing surgery. We outline current challenges in the field of breast cancer genetics and call for novel forms of multidisciplinary care and long-term evaluation.

Purpose Next to secondary epidermal growth factor receptor (EGFR) mutations, cMET amplification plays an important role in mediating acquired resistance to EGFR tyrosine kinase inhibitors (TKI) treatment. Crizotinib, a dual ALK and cMET inhibitor, can induce responses in patients with EGFR mutation positive non-small cell lung cancer (NSCLC) that acquire cMET amplification after EGFR TKI treatment. However, little is known about the duration of response and post-progression resistance mechanisms. Here, we report on the clinical outcome of a series of patients with cMET-driven resistance to EGFR TKIs, treated with crizotinib. Materials and methods Eight patients with EGFR mutation positive NSCLC that acquired cMET amplification after EGFR TKI treatment were treated with crizotinib 250 mg twice daily, as monotherapy (n = 2) or in combination with an EGFR TKI (n = 6). Results Four out of eight patients (50%) showed a partial response (PR) according to RECIST 1.1. Median progression-free survival (PFS) was 1.4 (95% CI 1.2–5.0) months. Responses were short-lasting with a median PFS of 3.5 (95% CI 1.4–5.2) months in patients with a PR. Median overall survival was 5.9 (95% CI 1.3–6.0) months and not statistically different between responders and non-responders (p = 0.37). All but one patient tolerated crizotinib treatment well. Heterogeneous responses were seen in patients with progressive disease as best response with a marked size decrease of the biopsied (cMET amplification positive) lesion and progression of other lesions. cMET amplification was not always mutually exclusive with other EGFR TKI resistance mechanisms. Post-progression biopsies were negative for cMET amplification. Conclusion Crizotinib treatment for patients with EGFR mutation positive NSCLC that acquire cMET amplification after EGFR TKI treatment results in short-lived and often heterogeneous responses, possibly due to subclonality of cMET-driven resistance and co-occurrence of other EGFR TKI resistance mechanisms.

Guanidinoacetate methyltransferase (GAMT) deficiency (MIM 601240), an autosomal recessive disorder of creatine biosynthesis, presents with mental retardation, extrapyramidal symptoms, autistic-like behavior and epilepsy. Other hallmarks are cerebral creatine deficiency, increased levels of guanidinoacetate in body fluids and mutations in the GAMT gene. Creatine supplementation partially restores cerebral creatine content. Worldwide, 29 patients have been identified and 15 different mutations have been reported in the GAMT gene. Ten out of these 29 patients are of Portuguese origin. Likely, a founder effect and a high carrier rate in Portugal exist, since in 17 out of the 20 Portuguese alleles the c.59G>C; p.Trp20Ser mutation was found. We investigated the carrier rate of the c.59G>C; p.Trp20Ser mutation in different regions of Portugal and confirmed the pathogenic nature of this missense mutation by transient transfections. Anonymous bloodspots (1002) were screened for the presence of the c.59G>C; p.Trp20Ser mutation by SNaPshot (Single Nucleotide Polymorphism Multiplex Kit). Eight carriers of c.59G>C; p.Trp20Ser were detected of which four are derived from the Archipelagos. This suggests that the carrier rate of the c.59G>C; p.Trp20Ser mutation is relatively high in these islands, as well as in other parts of Portugal. It also implies that newborn screening in these regions is warranted for this treatable disorder.

Guanidinoacetate methyltransferase deficiency (MIM 601240) is an autosomal recessive disorder of creatine biosynthesis. Patients present with mental retardation, extrapyramidal symptoms, autistic-like behavior, epilepsy, cerebral creatine deficiency and increased levels of guanidinoacetate. So far 15 mutations have been reported, including six missense variants that are highly likely to be pathogenic mutations. To prove that mutations in the GAMT gene are responsible for GAMT deficiency we overexpressed the GAMT open reading frame in GAMT-deficient fibroblasts by stable transfection. In addition, HeLa cells were transiently transfected with the same expression vector. In contrast to mock transfectants transfection of primary GAMT-deficient fibroblasts with wild-type GAMT results in the restoration of GAMT activity as measured by GC-MS using stable isotope labeled substrates. Moreover, the expression of the GAMT-EGFP fusion protein was analyzed by Western blot, confirming the presence of GAMT fusion protein, both in the stable as well as in the transient transfectants. Here, we prove that mutations in the GAMT gene are responsible for GAMT deficiency, since overexpression of the GAMT open reading frame restores GAMT activity in GAMT-deficient fibroblasts. Furthermore, the transient transfection of HeLa cells will be important for functional analysis of variants of unknown consequence (i.e., missense mutations).