Polymelia associated with frequent chromosome breaks in a heifer

POLYMELIA is a rare congenital defect characterised by the presence of a supernumerary limb at different locations on the body. Depending on the body region, polymelia has been classified as notomelia, cephalomelia, thoracomelia and pygomelia (Kim and others 2001). The phenomenon of polymelia is usually associated with other congenital defects such as polydactyly (extra fingers or toes) or the presence of additional and often underdeveloped bones (Murondoti and Busayi 2001). In most cases, the extra limb is shorter and devoid of muscle tissue. The physiological attributes of the affected animal, including temperature, pulse and respiration rate, are usually normal (Hirsbrunner and others 2002). This short communication describes polymelia in a heifer, associated with frequent chromatid/chromosome breaks observed in lymphocytes cultured in vitro. A black-and-white heifer, genetically 62·5 per cent Holstein-Friesian, was born with four normal legs and one extra limb localised in a shoulder girdle between the scapulas. The supernumerary limb was smaller than the normal legs, was bent at the carpal joint and had a terminal hoof. It hung down on the left side of the animal (Fig 1a). The extra limb was attached to an underdeveloped additional scapula, which was connected to the thoracic vertebrae. The animal underwent surgery on two occasions at three and four months of age. During the first operation the additional leg was removed at the shoulder joint. During the second operation, which was performed due to unsuccessful wound healing, only a part of the extra scapula was removed at the neck of the scapula; the whole scapula was not removed due to the risk of injury to the vertebral column. The skeleton of the additional limb, according to anatomical nomenclature (Dyce and others 1987), consisted of the stylopodium (humerus), zeugopodium (radius and ulna) and autopodium, including the basipodium (carpal bones), metapodium (metacarpal bones) and acropodium (proximal, middle and distal phalanges) (Fig 1b). The stylopodium consisted of a single long bone with distinguishable epiphysial cartilage of the proximal epiphysis and three unfused skeletal elements that made up the metaphysis. The diaphysis of the stylopodium, near the epiphysis, was laterally flattened. The appearance of this bone resembled a humerus. The zeugopodium included one long bone with a cleft in the diaphysis; however, the epiphyisis and metaphysis were jointed. It was not possible to conclude whether this bone was an element of a thoracic or pelvic limb. The basipodium consisted of carpal bones that were fused in two blocks not resembling the tarsal bones (there was no talus or calcaneus). The metapodium of the extra limb had features that were not typical of this segment of the autopodium in cattle. Two bones were partially fused together (a massive one and a very thin underdeveloped bone). The acropodium included the skeleton of two digits and contained three phalanges. One of the digits was well developed, and its middle and distal phalanges were combined. The other digit was smaller, with short and thin phalanges. The heifer was cytogenetically evaluated. Chromosome preparations were obtained from a peripheral blood lymFIG 1: Female calf with polymelia. (a) Localisation of the supernumerary limb in the shoulder girdle between the scapular. (b) Skeleton of the supernumerary limb. st Stylopodium (humerus), ze Zeugopodium (radius and ulna), ba Basipodium (carpal bones), me Metapodium (metacarpal bones), ac Acropodium (proximal, middle and distal phalanges)