Hartnup disease

Overview

A rare metabolic disorder involving an error in the transport of neutral amino acid and characterized by mental retardation, rash due to light sensitivity and cerebellar ataxia.

Symptoms

  • Itchy rash only on light exposed areas 
  • Headache 
  • Intermittent ataxia 
  • Abdominal pain 
  • Chest pain 
  • Pain in the extremities 
  • Crying spells 
  • Mental retardation if untreated
  • Fainting 
  • Psychotic reactions 
  • Thickened skin only on light exposed areas 
  • Scaly skin only on light exposed areas 
  • Increased skin pigmentation only on light exposed areas 
  • Dry hair 
  • Multicolored hair 
  • Rapid involuntary eye movements 
  • Hyperactive deep tendon reflexes 
  • Ataxic gait 
  • Excess amino acids in urine 
  • Double vision 
  • Short stature if untreated 
  • Emotional instability if untreated 
  • Dementia if untreated

Causes

* Orthopedic issues affecting the foot, ankle, leg, knee, or hip * Peripheral neuropathy (sensory and/or motor) –Slapping gait: Sensory neuropathies may result in a tendency to slap the feet firmly against the ground to improve proprioceptive input –Steppage gait: Seen in patients with foot drop –The classic tabetic gait combines both stepping and slapping gaits * Mononeuropathy/radiculopathy affecting the lower extremities may result in gait abnormalities (e.g., either a peroneal neuropathy or L5 radiculopathy can cause a unilateral steppage gait) o Myelopathy –Patients with bilateral lower extremity weakness and hypertonicity secondary to a spinal cord lesion may exhibit a spastic gait with stiffness of both legs and a tendency toward scissoring of the legs with walking o Brainstem or cortical lesions (e.g., multiple sclerosis, CVA) –Most commonly result in a hemiparetic gait with circumduction of the weak leg o Cerebellar lesions –Result in an ataxic gait, which tends to be wide-based, irregular, and staggering o Intoxications + Parkinsonism –Patients exhibit stooped posture, decreased arm swing, and shuffling (take many small steps) + Myopathies –Tend to produce a waddling gait because of weakness of the trunk, hip, and proximal lower extremity muscles + Spinocerebellar ataxia + Hereditary spastic paraparesis + Hysterical gaits + Inherited neuropathies (e.g., Charcot-Marie-Tooth disease) + GALOP syndrome (gait disorder, autoantibodies, late age onset, polyneuropathy) + Normal pressure hydrocephalus + Infection (e.g., neurosyphillis, meningitis) + Vitamin B12 or thiamine deficiency

Diagnosis

The wise clinician should consider a neurologic referral at the outset. If there is vertigo, tinnitus, or deafness, then an audiogram and caloric testing should be done. If these suggest eighth nerve damage, then a CT scan or MRI of the brain should be done. Headaches, sustained nystagmus, or papilledema are other indications for a CT scan or MRI. If multiple sclerosis is suspected, MRI of the brain is very useful, as well as spinal fluid for gamma globulin and myelin basic protein. Perhaps VEP, brain stem evoked potential (BSEP), or SSEP studies should be done. If vascular disease is suspected, magnetic resonance angiography will allow assessment of the vertebral-basilar arteries. If this is not available, four-vessel cerebral angiography may be utilized. Patients with hypoactive reflexes and glove and stocking hypoesthesia and hypalgesia will need a neuropathy workup . When there is ataxia in the presence of a normal neurologic examination, referral to a psychologist for psychometric testing should be done.