Convulsions, also known as convulsions, jerks, and frightening winds, are common emergency symptoms in children. Most of them are sudden, with loss of consciousness, staring with both eyes, squinting or turning upward, head tilted back, and tonic or clonic jerking of facial muscles and limbs; they may be accompanied by laryngospasm, apnea, or even cyanosis. There are often febrile convulsions and non-febrile convulsions (non-infectious diseases). The latter cause is often intracranial diseases such as epilepsy, traumatic brain injury, cerebral dysplasia, etc., and systemic diseases such as ischemic-hypoxic encephalopathy, water-electrolyte disorders, poisoning, vitamin deficiency, metabolic diseases, etc. The author encountered two cases of alternative convulsions – caused by methylmalonic acidemia – in the clinic, which I would like to introduce to you. Child A, male 3 months 15 days, second child first delivery (first child elective abortion), 37+1 weeks of pregnancy due to “premature rupture of amniotic fluid 10 hours” elective cesarean section, birth weight 2.9 Kg, denied history of asphyxia resuscitation. In the second month of pregnancy, she was kept in labor due to “placenta praevia bleeding”. The meconium was expelled 2-3 days after birth and jaundice persisted for 42 days. The child has a motor developmental delay, convulsions, and no odor of urine. Father: 32 years old, hepatitis B carrier, bank worker. Mother: 29 years old, teacher, physically fit. Denies consanguineous marriage. Denies family history of similar disease. Physical examination: body mass 7 Kg, body length 1575px head circumference 42 cm (nutrition evaluation medium +) reactive, facial reflexes present, audiovisual reflexes present, skin mucosa not pigmented and milk coffee spots, skull orthotropic, features correct, fontanelle flat and soft 1.0×25px, physiological reflexes present, primitive reflexes asymmetrical tension neck reflexes present, pathological reflexes positive for Bartholomew’s sign, Vojta Postural reflex 7/7 abnormal, upright reflex and balance reflex were not established. Motor developmental examination: supine position: difficult to center the head, little movement of hands in midline position, occasionally able to turn over; prone position: unable to actively lift the head, no elbow support, no hand support; sitting position: full forward tilt; standing position: unable to support the body mass; full hand grasp, high muscle tone in all limbs, femoral angle 900, N angle 1350, foot dorsiflexion angle 700, scarf sign did not cross the midline; language and intelligence evaluation slightly behind; no enlargement of liver and spleen. Rehabilitation assessment: gross motor 1 month, fine motor 3 months, cognitive ability 3 months, language ability 3 months, social behavior 3 months. Cephalometric CT: enlarged lateral ventricles, bilateral subdural effusion on top of the frontal area. Bone density: decreased bone mass. Hematology: hemoglobin concentration 105 g/L, erythrocyte pressure volume 33, mean hemoglobin content 25.72 pg, mean hemoglobin concentration 318.9 g/L, platelets 84×109/L, all decreased. EEG, brain topography, brainstem evoked potentials, somatosensory evoked potentials, chest and pelvis X-ray, infectious disease IV, thyroid function, blood biochemistry, urine routine, and fecal routine were normal. The urine screening test reported methylmalonic acidemia. This child was given vitamin B12 0.5mg intravenous push once a day on the basis of a low-protein diet, which was changed to oral vitamin B12 0.5mg once a day after 7 days of treatment, combined with other rehabilitation treatments, and achieved very satisfactory results, with no convulsions and significant progress in mental and motor development. After discharge from the hospital, the child continued to take vitamin B12 and was followed up for 1 year. At present, the child is 1 year and 3 months old, no convulsions, able to walk alone, conscious calling, and growth and development like a child of age. The child is 6 months and 17 days old, the third child was born first (the first child was stillborn in the third month of pregnancy and the second child was spontaneously aborted in the second month of pregnancy), and was delivered by full-term elective cesarean section. She worked in a heavily air polluted environment during early pregnancy. History of jaundice was not detailed. The child has delayed motor development, lifted his head at 3 months, now 6 months and 17 days with unstable vertical head and no odor of urine. Father: 27 years old, physically fit, worker in a lamp factory. Mother: 25 years old, hepatitis B virus carrier, lamp factory worker. Denies consanguineous marriage. Denied family history of similar disease. Physical examination: body mass 10 Kg, length 1750 px head circumference 42.5 cm (nutrition evaluation in +), retrospective inflexibility, fair response to sound, no pigmentation or milk coffee spots on skin mucosa, skull orthotropic, good features, fontanelle flat and soft 1.0 x 25 px. primitive reflexes foot grasp reflex: left (+), right (-); lateral bending reflex present. Physiological reflexes Knee reflex: left side (+), right side (++). Pathological reflexes were not elicited, Vojta postural reflex 5/7 was abnormal, upright reflex and balance reflex were not established. Motor development examination: supine position: head can be centered, bilateral limbs are symmetrical, no active hand grasp awareness, no centerline activity, hands can easily clench fists; prone position: can actively lift head to 900, with active elbow support and left elbow can support alone for a few seconds, no hand support; sitting position: can’t sit; standing position: both lower limbs are stiff and straight extension, visible pointed feet, no knee dystocia and scissor step; full hand grasp, limb muscle tone is unstable, tension The femoral angle was 900, the N angle was 1100, the dorsiflexion angle of the foot was 900 on the left and 1000 on the right; 700, the scarf sign did not cross the midline; poor cognitive ability; no enlargement of the liver and spleen. Child development scale: intelligence equivalent to 1 month level, motor equivalent to 1.4 months level. Cephalometric MRI: brain hypoplasia. Somatosensory evoked potentials: 1. prolonged latency and decreased amplitude of the main wave N20 of the SEP cortical wave in the left upper limb, and approximately normal latency of the main wave N20 of the SEP cortical wave in the right upper limb; 2. prolonged latency and decreased amplitude of the main wave P40 of the somatosensory evoked potentials in both lower limbs. Hemoglobin concentration 128g/L, erythrocyte pressure volume 36.6, mean erythrocyte volume 77.72fl, platelets 480.40×109/L elevated, mean platelet volume 8.74fl decreased, platelet pressure volume 0.42 elevated. Urine lactose (+), PH 5.5. EEG, brain topography, brainstem evoked potentials, visual evoked potentials, chest and pelvic X-ray, infectious disease IV, thyroid function, blood biochemistry, urine routine and fecal routine were normal. The urine screen reported methylmalonic acidemia. This child was given vitamin B12 0.5mg intravenous push once a day on the basis of low protein diet, and then changed to oral vitamin B12 0.5mg once a day after 7 days of treatment, combined with other rehabilitation treatment, and achieved very satisfactory results, with significant progress in mental and motor development, and urinary methylmalonic acid decreased from 2.5 times to 1.6 times the normal value. However, he failed to take vitamin B12 in time after discharge from the hospital. After 1 year of follow-up, his intellectual and motor development was significantly backward, and he gradually developed refractory convulsions and vomiting, and ordinary antiepileptic treatment was ineffective. After that, vitamin B12 0.5 mg was given twice a day by intramuscular injection, and three days later, vitamin B12 0.5 mg was given orally once a day, and there were no more convulsions and vomiting, but the recovery of mental and motor development was not as obvious as before. The difference in prognosis between children A and B is very obvious, so what is methylmalonic acidemia? Methylmalonic acid in methylmalonic acidemia is a metabolite of methylmalonyl coenzyme A in the catabolic pathway of cholesterol, odd-chain fatty acids, threonine, methionine, isoleucine and valine, which is converted to succinic acid by the action of methylmalonyl coenzyme A metastase and its coenzyme vitamin B12 to participate in the tricarboxylic acid cycle. Defective metabolism of methylmalonyl coenzyme A or vitamin B12 leads to abnormal accumulation of metabolites such as methylmalonic acid, propionic acid and methylcitrate, resulting in structural brain damage such as mitochondrial dysfunction, neuronal apoptosis, altered cytoskeletal phosphorylation and impaired myelin formation; developmental brain damage such as abnormal ganglioside and synaptic plasticity; and functional brain damage such as cognitive and behavioral changes The diagnosis of the disease is based on urine screening analysis to identify the abnormal composition of the urine of the child. Definitive diagnosis relies on enzymatic analysis of skin fibroblasts, lymphocytes, liver tissue fibroblasts or genetic diagnosis. There are many causes of convulsions, and when we consider a metabolic disease that is not a common cause, a urine screening test may have unexpected rewards, which can be called “a village in the dark.”