Page 69 - Haematologica3

SAMD9L-related familial MDS
transfected cells were tracked by flow cytometry for TFP- SAMD9L expression and dye dilution as an indicator of cell divi- sion. SAMD9L variant p.T233N, recently reported as “disease-pro- tective”,20 was used as a control.
Results
Clinical phenotype of patients
Patients P1-P6 (4 males and 2 females) belong to three unrelated families of German descent and were diagnosed with bona fide familial MDS after known inherited bone marrow failure syndromes had been excluded by targeted sequencing and functional tests (Figure 1, Table 1). Index patient P7 is the only child of a non-consanguineous
A
Swedish family. Detailed clinical descriptions of all the patients are given in the Online Supplementary Material. All affected individuals had normal measurements without dysmorphic stigmata at birth and at last follow-up (Table 1). Psychomotor development and neurocognitive function were normal and, in particular, no ataxia or movement dis- orders were diagnosed in the ten mutation carriers (7 patients and 3 silent carriers with SAMD9L mutations). Previous family histories were unremarkable for cytope- nias, neurological disease, malignancies, or stillbirths, with the exception of the father of P7 who at the last follow-up presented with unclear ataxia. Prior non-invasive recurrent respiratory tract infections were noted in three of the seven patients (P1, P2, and P4) and endogenous eczema in two (P1 and P3). Moreover, P1 developed transient pancytope-
BC
Figure 1. Germline SAMD9L mutations in pedigrees with familial myelodysplastic syn- drome. (A) Identification of four pedigrees with MDS and mono- somy 7 harboring germline het- erozygous SAMD9L mutations: p.V1512M (pedigree I), p.R986H (pedigree II) and p.R986C (pedi- gree III), p.H880Q (pedigree IV), and somatic mutations: p.R1188X (P1) and p.S1317RfsX21 (P7). Dotted sym- bols indicate healthy mutation carriers. Sanger sequencing on DNA extracted from hair follicles (HR) confirmed the germline sta- tus of mutations as visualized in electropherograms. Sequencing in P1 was performed on peripher- al blood granulocytes (GR) reveal- ing a minor mutational peak, cor- responding to a variant allelic fre- quency of 8.3% by whole exome sequencing. In pedigree III, the mutation in P5 was confirmed in fibroblast (FB) DNA, while for P6 and remaining family members whole blood (WB) was analyzed. In pedigree IV other family mem- bers were not tested (n.t.). (B) SAMD9L and SAMD9 gene orien- tation on 7q22 in reverse strand direction (3‘-5‘). The SAMD9L pro- tein is coded by one exon and contains two known functional sites: N-terminal sterile alpha motif (SAM) and nuclear localiza- tion sequence (NLS). Four germline and two somatic (*) mutations were identified in SAMD9L. Germline missense mutations are evolutionarily high- ly conserved. (C) TA cloning of the double mutated SAMD9L region of P1 revealed cis-configuration of mutations p.V1512M (germline) and p.R1188X (somat- ic) in ten out of 172 clones tested.
haematologica | 2018; 103(3)
429