Most family members to walk on all fours

Five (out of 19) adult siblings of the Ulas family of Turkey - four sisters and a brother - walk on their feet and the plams of their hands. This quadrupedal gait (known as "bear walk") is unique to the Ulases and is different to the "knuckle walk" witnessed in the great apes. The five siblings also suffer from congenital brain impairment and have trouble balancing on two legs. The condition is known as Uner Tan Syndrome, after the Turkish professor at Cukurova University, Turkey, who first studied the family in 2005. Each quadruped has a recessive mutation on chromosome 17. However, some researchers argue that the "bear walk" is a result of the siblings' congenital brain impairement and their inability to remain balanced on two legs, rather than a specific syndrome.