Cardiomyopathy with lethal arrhythmias associated with inactivation of KLHL24

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disorder, yet the genetic cause of up to 50% of cases remains unknown. Here, we show that mutations in KLHL24 cause HCM in humans. Using genome-wide linkage analysis and exome sequencing, we identified homozygous mutations in KLHL24 in two consanguineous families with HCM. Of the 11 young affected adults identified, 3 died suddenly and 1 had a cardiac transplant due to heart failure. KLHL24 is a member of the Kelch-like protein family, which acts as substrate-specific adaptors to Cullin E3 ubiquitin ligases. Endomyocardial and skeletal muscle biopsies from affected individuals of both families demonstrated characteristic alterations, including accumulation of desmin intermediate filaments. Knock-down of the zebrafish homologue klhl24a results in heart defects similar to that described for other HCM-linked genes providing additional support for KLHL24 as a HCM-associated gene. Our findings reveal a crucial role for KLHL24 in cardiac development and function.

Mutations in INPP5K Cause a Form of Congenital Muscular Dystrophy Overlapping Marinesco-Sjögren Syndrome and Dystroglycanopathy

Congenital muscular dystrophies display a wide phenotypic and genetic heterogeneity. The combination of clinical, biochemical, and molecular genetic findings must be considered to obtain the precise diagnosis and provide appropriate genetic counselling. Here we report five individuals from four families presenting with variable clinical features including muscular dystrophy with a reduction in dystroglycan glycosylation, short stature, intellectual disability, and cataracts, overlapping both the dystroglycanopathies and Marinesco-Sjögren syndrome. Whole-exome sequencing revealed homozygous missense and compound heterozygous mutations in INPP5K in the affected members of each family. INPP5K encodes the inositol polyphosphate-5-phosphatase K, also known as SKIP (skeletal muscle and kidney enriched inositol phosphatase), which is highly expressed in the brain and muscle. INPP5K localizes to both the endoplasmic reticulum and to actin ruffles in the cytoplasm. It has been shown to regulate myoblast differentiation and has also been implicated in protein processing through its interaction with the ER chaperone HSPA5/BiP. We show that morpholino-mediated inpp5k loss of function in the zebrafish results in shortened body axis, microphthalmia with disorganized lens, microcephaly, reduced touch-evoked motility, and highly disorganized myofibers. Altogether these data demonstrate that mutations in INPP5K cause a congenital muscular dystrophy syndrome with short stature, cataracts, and intellectual disability.