Complex effects of laminopathy mutations on nuclear structure and function.

The nuclear lamins are important members of the intermediate filament (IF) family of proteins, involved in structural support and regulation of the nuclear lamina. Different mutations in various members of these type V IF proteins produce a staggering range of human disease phenotypes, which collectively have been termed "laminopathies." Compelling examples are the wide range of inherited disorders that result from rare variants in LMNA encoding lamin A/C. These laminopathies include skeletal and cardiac muscle disorders, neuropathies, multisystem progeroid disorders, and lipodystrophies, of which the latter are associated with several metabolic complications. Functions of lamin A/C that have been shown to be compromised by distinct mutations in LMNA include loss of nuclear structural integrity, altered interaction with transcription factors, and changes to post-translational processing of pre-lamins. Recently, evidence has emerged that certain LMNA mutations, such as those causing partial lipodystrophy, alter the interaction between chromatin and lamin A, in turn affecting the spatial orientation and distribution of chromatin within the nucleus. Because chromatin organization is exquisitely tied to global patterns of gene expression, the findings suggest a novel mechanism to explain the tissue-specific impact of a subset of laminopathy-associated LMNA mutations.

Whole-exome sequencing identifies a novel IHH insertion in an Ontario family with brachydactyly type A1.

Isolated brachydactyly is an umbrella term describing disproportionally shortened fingers and toes, often following an autosomal dominant mode of inheritance. Various forms of brachydactyly have been characterized and several causative genes have been found, but many types remain genetically undefined. We describe an Ontario family with mild brachydactyly in which whole-exome sequencing identified a novel variant for brachydactyly type A1 (exon 1, c.285_287dupGAA, p.Glu95_Asn96insLys) in the Indian hedgehog (IHH) gene. This rare variant co-segregated with affected status in the pedigree and was associated with (1) shortened middle phalange length by 21.1% (p < 0.001); (2) shortened palm length by 13.8% (p < 0.01); (3) reduced digit-palm ratio by 6.8% (p < 0.03); and (4) reduced stature by 9.5% (p < 0.001). We report the first IHH in-frame insertion causing brachydactyly type A1.