Hydrolethalus syndrome

Hydrolethalus syndrome, abbreviated HLS, is a rare genetic disorder that disrupts fetal development and causes birth defects, most commonly ending in stillbirth. It is associated with mutations in the HYLS1 gene, which is needed for proper development of cilia, the microscopic projections that let cells receive sensory input, send signals and move. When cilia do not form properly, cell signalling goes wrong and a range of abnormalities follows. A less common variant, HLS2, involves additional mutations in the KIF7 gene, which also governs cilia formation, stability and length. The condition was first mistakenly identified in Finland during a study of Meckel syndrome, which shares severe abnormalities of the central nervous system and extra fingers or toes. Analysis of kidney function separates the two, because the kidneys are dysfunctional in Meckel syndrome as a result of cyst formation.