Rare Missense Variants in MYH11 and MYLK are associated with Prune Belly Syndrome
Nathalia G. Amado, PhD1, Thomas J. Egeland, MS1, Michelle S. Yang, MS1, Shahher Ali, MS1, Shane Batie, MD2, Caitlin T. Coco, MD2, Katelynn Sagaser, MD3, Angie Jelin, MD3, Jeremy Mathews, MS1, Brandi Cantarel, PhD1, Linda A. Baker, MD1.
1UT Southwestern Medical Center, Dallas, TX, USA, 2Childrens Health Dallas - UTSW, Dallas, TX, USA, 3Johns Hopkins University School of Medicine, Baltimore, MD, USA.
BACKGROUND: Smooth Muscle Myopathies (SMM) are a group of autosomal dominant or recessive genetic disorders leading to dysfunctional vascular and/or visceral smooth muscle, presenting in neonates to adults. Depending on affected gene and specific mutation, the phenotypic spectrum encompasses: Thoracic aortic aneurysm and dissection (TAA/D), Visceral myopathy, Multisystemic Smooth Muscle Dysfunction Syndrome, and Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS). Many cases of SMM are caused by DNA variants in MYH11 and MYLK. Using a biased approach, we investigated whether PBS might be associated with MYH11 and MYLK variants. METHODS: With IRB-approval, PBS probands and family members were prospectively enrolled and phenotyped. Proband blood lymphocyte DNA underwent paired-end Whole Exome Sequencing (WES) using the Illumina SureSelect kit and HiSeq2500 sequencer, with data pipeline analysis. Variants were filtered for rare minor allele frequency (<0.001) and their potential functions were predicted using in silico-based computational analysis. Variants meeting ≥5 of the following criteria were selected as suspected functional variants: SIFT < 0.1, Polyphen2 > 0.9, CADD score > 20, GERP > 4, MutationTaster = "A" or "DC", Mutation Assessor= "M" or "H", and Vest > 3.00 (Figure 1C). Rare and novel variants were screened in ClinVar database for prior association with SMM. After Sanger sequencing confirmation, familial segregation was investigated on available samples. Available PBS and non-PBS control bladder tissues were formalin fixed, paraffin embedded, and stained with Masson's trichrome. RESULTS: 132 PBS probands underwent WES. After variant filtering, 13 male probands demonstrated 12 rare or novel heterozygous missense variants in MYH11 (6 probands, 5 variants) (Figure 1A&C) or MYLK (7 probands, 7 variants) (Figure 1B&C). Previously, 8 of 12 variants have been associated with TAA/D and classified as uncertain significance on ClinVar due to lack of functional characterization. Interestingly, none of these PBS variants have been previously reported in MMIHS. Four MYH11 variants (R108W, A699V, T1565M and K1628Q) in five PBS probands are maternally inherited from asymptomatic mothers and one variant (A699V) was also found in a non-affected brother, suggesting incomplete penetrance or additional modifier genes in the proband. Bladder pathological analysis was possible on 1 PBS proband (PBS-8), highlighting severe disorganization of detrusor smooth muscle bundling with extensive collagen deposition (Figure 1D). CONCLUSION: By screening for rare or novel DNA variants in genes known to cause smooth muscle myopathies, we identified 13 PBS probands (~10% of our PBS cohort) with 5 MYH11 and 7 MYLK mutations. Different mechanisms of MYH11 or MYLK disruption, tissue specific regulation and unique mutant protein interactions may yield distinct patterns of smooth muscle dysfunction and can lead to distinct rare pathologies. Thus, longitudinal studies on PBS cases harboring these smooth muscle myopathy genes are needed to assess risk for life-threatening TAAD for long term health counseling. Our data suggest that PBS is a heterogeneous and complex disorder that can be explained in part by heterozygous mutations in MYH11 and MYLK.
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