Genetic landscape of congenital insensitivity to pain and hereditary sensory and autonomic neuropathies.

Congenital insensitivity to pain (CIP) and hereditary sensory and autonomic neuropathies (HSAN) are clinically and genetically heterogeneous disorders exclusively or predominantly affecting the sensory and autonomic neurons. Due to the rarity of the diseases and findings based mainly on single case reports or small case series, knowledge about these disorders is limited. Here, we describe the molecular workup of a large international cohort of CIP/HSAN patients including patients from normally under-represented countries. We identify 80 previously unreported pathogenic or likely pathogenic variants in a total of 73 families in the >20 known CIP/HSAN-associated genes. The data expand the spectrum of disease-relevant alterations in CIP/HSAN, including novel variants in previously rarely recognized entities such as ATL3-, FLVCR1- and NGF-associated neuropathies and previously under-recognized mutation types such as larger deletions. In silico predictions, heterologous expression studies, segregation analyses and metabolic tests helped to overcome limitations of current variant classification schemes that often fail to categorize a variant as disease-related or benign. The study sheds light on the genetic causes and disease-relevant changes within individual genes in CIP/HSAN. This is becoming increasingly important with emerging clinical trials investigating subtype or gene-specific treatment strategies.

Vitamin A toxicity presenting as bone pain.

A 4-year-old boy presented with severe bone pains, refusal to walk, diffuse bony swelling of forelimbs, skin changes and abdominal pain, with symptoms evolving over 6 weeks. Blood screening tests were normal except for raised aspartate aminotransferase (AST). Radiographs revealed thickened periosteum, widening of the diaphyses of long bones and lifted periosteum in mid-shaft of ulnae and right femur. Skeletal scintigraphy showed a high uptake of radionuclide at clinically affected and unaffected sites, suggestive of multifocal osteoblastic skeletal lesions. After repeated enquiries, his parents admitted to giving him massive doses of preformed vitamin A for over 3 months as 'health tablets'. Surprisingly, he did not have overt liver disease typically found with much smaller doses, although the dermal changes and musculoskeletal pathology were florid. He made a full clinical recovery within 2 months of cessation of vitamin A.