COL11A1 and Stickler syndrome: Few heterozygous COL11A1 mutations resulting in haploinsufficiency have been associated with Stickler syndrome manifestations [30], and the paucity of symptoms in patients with a heterozygous null allele can also be confirmed when looking at families with homozygosity or compound heterozygosity: parental carriers are often asymptomatic or exhibit only mild symptoms [31].