Neurophysiological studies, including EMG and focal magnetic brain stimulation, were used to evaluate possible mechanisms for mirror movements in 14 male patients, aged 16-60 years, with X-linked Kallmann’s syndrome compared to controls at the Department of Physiology, University College London, UK. During EMG recording from the first dorsal interosseous muscle (1DI) with voluntary abduction of an index finger, mirror EMG activity was recorded simultaneously from the contralateral 1DI. Focal magnetic stimulation of the hand area of the motor cortex revealed inter- and intra-subject differences in the ratio of ipsilaterally to contralaterally projecting corticospinal axons. Multi-unit EMGs during simultaneous voluntary activation of distal upper limb muscles showed a central peak in the cross-correlograms, indicating a common drive to left and right homologous motor neuron pools. A synchronous activation of intermingled ipsilateral and contralateral corticospinal neurons could explain this common drive. Long latency trans-cortical components of a cutaneomuscular reflex recorded from the 1DI following digital nerve stimulation could be recorded simultaneously from the 1DI of the non-stimulated side. Activity in a novel ipsilateral corticospinal tract is proposed as the mechanism for pathological mirror movements in X-linked Kallmann’s syndrome. 
COMMENT. The X-linked form of Kallmann’s syndrome (KS) is characterized by hypogonadotrophic hypogonadism, anosmia, unilateral renal agenesis, and mirror movements. An adolescent male of eunuchoid build, referred to the neurologist because of attention, coordination, and cognitive deficits, should be considered for olfactory tests and an MRI of the brain, for aplasia of the olfactory system. (see Progress in Pediatric Neurology II, PNB Publ, 1994;p309). The abnormal mirror movements observed in 85% of adult patients with KS are a normal and frequent finding in children under 7 years of age. The persistence of mirror movements, often observed in older children with ADHD, can be a sign of “minimal brain dysfunction,” and an inability to inhibit activity in the ipsilateral corticospinal tract during rapid alternating movement of one hand. A defect or delay in myelination of callosal fibers has been suggested as the underlying pathology for persistent mirror movements. They are often present with callosal agenesis. In KS patients the defect may also extend to other axonal fibers in the frontal motor and olfactory systems, and involving a novel abnormal ipsilateral corticospinal tract.
In a further study using PET and regional cerebral blood flow, at the Wellcome Department of Cognitive Neurology, Queen Square, London, six right-handed male subjects with KS showed activation in the motor cortex both contralateral and ipsilateral to the voluntarily moved hand, although the contralateral activation was significantly stronger. Activation of the ipsilateral motor cortex in KS may be caused by sensory feedback from the involuntarily mirroring hand.