Novel 25 kb Deletion of MERTK Causes Retinitis Pigmentosa With Severe Progression.
Retinitis pigmentosa (RP) describes a complex group of inherited retinal dystrophies with almost 300 reported genes and loci. We investigated the genetic etiology of autosomal recessive RP (arRP) in a large kindred with 5 affected family members, who reside on the island of Newfoundland, Canada.



Genetic linkage analysis was performed on 12 family members (Infinium HumanOmni2.5-8 BeadChip). Whole exome sequencing analysis (Illumina HiSeq) was performed on one affected individual. A custom pipeline was applied to call, annotate, and filter variants. FishingCNV was used to scan the exome for rare copy number variants (CNVs). Candidate CNVs subsequently were visualized from microarray data (CNVPartition v.3.1.6.). MERTK breakpoints were mapped and familial cosegregation was tested using Sanger Sequencing.



We found strong evidence of linkage to a locus on chromosome 2 (logarithm of the odds [LOD] 4.89 [θ = 0]), at an interval encompassing the MERTK gene. Whole exome sequencing did not uncover candidate point mutations in MERTK, or other known RP genes. Subsequently, CNV analysis of the exome data and breakpoint mapping revealed a 25,218 bp deletion of MERTK, encompassing exons 6 to 8, with breakpoints in introns 5 (chr2:112,725,292) and 8 (chr2:112,750,421). A 48 bp insertion sequence was buried within the breakpoint; 18 bps shared homology to MIR4435-2HG and LINC00152, and 30 bp mapped to MERTK. The deletion cosegregated with arRP in the family.



This study describes the molecular and clinical characterization of an arRP family segregating a novel 25 kb deletion of MERTK. These findings may assist clinicians in providing a diagnosis for other unsolved RP cases.
Discipline of Genetics, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
Daniel R
DR
Evans
Discipline of Genetics, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
Jane S
JS
Green
Department of Surgery (Ophthalmology), Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
Gordon J
GJ
Johnson
Department of Human Genetics, McGill University, Montréal, Québec, Canada 4McGill University and Genome Québec Innovation Centre, Montréal, Québec, Canada.
Jeremy
J
Schwartzentruber
Department of Human Genetics, McGill University, Montréal, Québec, Canada 4McGill University and Genome Québec Innovation Centre, Montréal, Québec, Canada.
Jacek
J
Majewski
Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
Chandree L
CL
Beaulieu
Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
Wen
W
Qin
Program in Genetics and Genome Biology, The Center for Applied Genomics, The Hospital for Sick Children Research Institute, and Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
Christian R
CR
Marshall
Program in Genetics and Genome Biology, The Center for Applied Genomics, The Hospital for Sick Children Research Institute, and Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
Tara A
TA
Paton
Program in Genetics and Genome Biology, The Center for Applied Genomics, The Hospital for Sick Children Research Institute, and Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
Nicole M
NM
Roslin
Program in Genetics and Genome Biology, The Center for Applied Genomics, The Hospital for Sick Children Research Institute, and Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
Andrew D
AD
Paterson
Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
Somayyeh
S
Fahiminiya
Western Memorial Regional Clinic (Eye Care Centre), Corner Brook, Newfoundland, Canada.
Justin
J
French
Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
Kym M
KM
Boycott
Discipline of Genetics, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
Michael O
MO
Woods
D000595:Amino Acid Sequence; D004247:DNA / Q000235:genetics*; D018450:Disease Progression; D059472:Exome; D005260:Female; D005808:Genes, Recessive; D008040:Genetic Linkage; D006801:Humans; D008297:Male; D010375:Pedigree; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism; D012174:Retinitis Pigmentosa / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017384:Sequence Deletion / Q000235:genetics*; D012720:Severity of Illness Index; D000076202:c-Mer Tyrosine Kinase
D011518:Proto-Oncogene Proteins; D004247:DNA; C097072:MERTK protein, human; D020794:Receptor Protein-Tyrosine Kinases; D000076202:c-Mer Tyrosine Kinase