Glossary of terms associated with Lissencephaly

Having struggled to understand detailed clinical and genetic papers on Lissencephaly I thought  a glossary of specific terms would help make things a little clearer.

For a list of abbreviations Click Here


   a- not, absent  - like agenesis
     absence seizure transitory interruption of conciousness without convusion (petit mal)
     agenesis of the corpus callosum the corpus callosum failed to develop during pregnancy
    agyria absence of gyri giving a smooth surface to part or all of the brain
  allele a gene found in the same location on a pair of homologous chromosomes
    anoxia no oxygen
   apnea a temporary cessation of breathing
ataxia inability to coordinate voluntary muscle movements; unsteady movements and staggering gait
   atonic drop attack seizure which involves a sudden loss of muscle control
    autosomal an inheritance pattern indicating that the gene involved is not on one of the sex chromosomes. It is the opposite of sex-linked, or X-linked, or Y-linked.
    aversive seizure seizure in which the head, eyes, or trunk turn to one side
      Bard button plastic device fitted into the tummy -form of G-tube
    bi-temporal hollowing a narrowing of the head at the temples
   brachycephaly having a comparatively short head
   bradycardia slow heartbeat
   brain stem a part of the brain located at the top of the spinal chord that performs many of the low level brain functions (e.g. breathing)
    calcification the hardening of a tissue by a deposit of calcium salts
   cavum septum pellucidum the membranous partition that separates the frontal horns of the ventricles
   cerebellar vermis 1. either of two parts of the median lobe of the cerebellum: a) one slightly prominent on the upper surface -- also called superior vermis b)  one on the lower surface sunk in the vallecula -- also called inferior vermis
2.  the median lobe or part of the cerebellum
   cerebrum the main bulk of the brain, formed by the cortex and white matter
   cerebellum a small part of the brain located behind and below the cerebrum
   chromosome each of the individual structures of DNA and protein found in the nuclei of cells that carry the genetic information in the form of genes.  A chromosome generally has two arms known as the 'p' and 'q' arm.
   cisterna magna a space containing fluid between the cerebellum and medulla oblongata
   Classical Lissencephaly an umbrella term which encompasses MDS, ILS, SBH and Baraitser-Winter syndrome
   clinodactyly a deformity of the hand marked by deviation or deflection of the fingers.
   colpocephaly enlargement of the posterior horns of the ventricles
   complex partial seizure loss of consciousness but may still allow the person to perform simple tasks
   contrast (in MRI or CT) "with contrast" means that a substance was injected into a vein so that it fills the blood vessels of the brain so that they are visible in the scan.
      clonus repeated quick spasms
   cortex the outer part of the brain which normally consists of 6 layers of nerve cell bodies
     cortical visual impairment (CVI) a condition where the brain is unable to accurately interpret what it sees.  The actual eyes generally function OK with this condition.
   corpus callosum part of the brain that joins the two hemispheres together
   CT (scan) Computerised Tomography - the use of X rays and computers to produce an image of an organ
   cryptorchidism the testicles fail to descend before the child is born
   cytomegalovirus (CMV) CMV is a member of the herpes group of viruses, usually spread through close person to person contact.  Can cause neurological development problems if contracted during pregnancy.
  DCX the name of the X-linked gene associated with Lissencephaly and Subcortical Band Heterotopia. Located on the X chromosome at Xq22.3-q23.  Also known as XLIS.
   de novo a new occurrence (applied to a new genetic mutation)
  deletion a missing part of a chromosome or gene
   dominant (autosomal -) (and it's opposite recessive) - inheritance pattern indicating that only one mutant copy of the gene is required to get the disease.
   dys- abnormal, wrong
   dysarthria difficulty of speech or articulation
  dysfunction abnormal functioning
   dysgenesis created incorrectly
  dysmorphic an anatomical malformation unusual features of the face or other organ or structure.
  dysphagia difficulty in swallowing
  dysplasia a formation of abnormal  tissue (structurally wrong)
     -ectomy cut out, remove
  EMX2 gene that is implicated in some cases of Schizencephaly.
       encephalocoele hernia of the brain that is either congenital or due to trauma.
     epicanthal fold a fold of skin around the eye. Epicanthus tarsalis is where the fold is most prominent in the upper eyelid. Epicanthus inversus is if the fold is most prominent in the lower eyelid. Epicanthus palpebralis is distributed equally in the upper and lower eyelid, and epicanthus supraciliaris is if the fold arises from the eyebrow extending to the lacrimal sac.
   facial diplegia symmetrical paralysis of the same muscles on both sides of the face
FCMD gene that is implicated in Fukyama Muscular Dystrophy located at 9q31
    FISH Fluorescence In Situ Hybridisation - a laboratory test for detecting genetic faults in chromosomes
FLNA/FLN1/Filamin gene that is implicated in Bilateral Periventricular Nodular Heterotopia (BPNH) located at Xq28
    focal seizure motor seizure which begins in one part of the brain (and hence body) and then spreads to other muscle groups.  There is no loss of conciousness.
   frontal lobe the front part of the cerebrum
    G-tube a feeding tube that goes straight into the stomach (G=gastric)
    genotype the genetic constitution of an individual.
   glia this is an old word that means "glue". Scientists used to think that glial cells were the glue that held the neurons in place in the brain, but now we know that they do lots of things. They make myelin. Other types of glia act to remove potassium ions from the spaces just outside neurons in the brain. (Neurons release potassium each time the generate an electrical signal.) One prominent theory of epilepsy is that the glia don't remove potassium well enough and its accumulation outside neurons causes them to fire out of control electrical signals, causing a seizure.
    gliosis a proliferation of glial cells around a site of injury to the brain.
grade 1,2,3,4,5,6 a classification system for ILS/MDS which grades the smoothness of the brain
    grey matter where nerve cell bodies are located and where most information-processing occurs. It looks pinkish grey because of all the small blood vessels there
   gyri the folds or convolutions normally seen on the surface of the brain
   haploinsufficiency mutation in the heterozygous state which result in half normal levels of the gene product
   hemisphere the two main parts of the cerebrum
   heterotopia occurring in an abnormal place
   heterozygote an individual who posses two different alleles in the the same chromosome pair
   homology having the same structural features and pattern of genes
   hydrocephalus large head circumference caused by fluid build up in the skull
   hyper- greater than or more than normal
   hypertelorism excessive width between two bodily parts or organs (usually used to describe a broadened space between the eyes)
   hypertonia stiff muscles
   hypo- less than or smaller than normal
    hypotonia floppy muscles
   hypoplasia incomplete, arrested or underdevelopment of an organ or tissue
  hypoxia too little oxygen
   iatrogenic caused by the physician or by the treatment.
   icthal during an actual seizure. (a seizure is an ictal event)
   infantile spasm (IS) bouts of sudden bilateral contraction of the muscles of the neck, trunk and extremities with sudden flexion of the arms and legs -  also known as West's syndrome
   Isolated Lissencephaly Sequence (ILS) a brain showing agyria and/or pachygyria but with no other symptoms
  J-tube a feeding tube that bypasses the stomach completely and goes straight to the small intestine (J=jejunum)
   karyotype a complete set of chromosomes from a cell nucleus
    Lennox-Gastaut syndrome a seizure disorder characterised by multiple seizure types
    LIS1 the name of the gene located on the short arm (p) of chromosome 17 (17p13.3) that is associated with Miller Dieker Syndrome, some cases of ILS and some case of Lissencephaly with Cerebellar Hypoplasia (a)
     Lissencephaly an umbrella term which encompasses a broad range of different conditions which affect the development of the cerebral cortex, where the surface of the brain appears smooth. See Classical Lissencephaly
locus the location on a chromosome, quoted in the form 17p13.3  (17 = chromosome 17, p = short arm)
     macrogyri large gyri
     MEB Muscle-Eye-Brain disease.  Also, the Muscle-Eye-Brain disease gene.  Located on chromosome 1 at 1p32-34
     Miller-Dieker syndrome agyric and/or pachgyric brain with other symptoms, generally bitemporal hollowing, prominent forehead, short nose with upturned nares, prominent upper lip, thin vermilion border of the upper lip, and small jaw.
    microcephaly small head circumference
     microdeletion a small part of a gene or chromosome that is missing
       microencephaly small brain size
       micrognathia small chin
    midline the midline is the line in the body that divides left from right.
    monosomy a single chromosome when there would normally be two
     MRI (scan) Magnetic Resonance Imaging - a sophisticated scanning technique for viewing internal organs.   MRI produces better images than CT.
   myelin the insulating coating around the axons of nerve cells
     nares nostrils
    neuronal migration disorder (NMD) a disorder where the cells in the brain do not move to their correct position during its developmental phase
NUDEL a protein that forms a key part of the neuronal migration process
    nystagmus a wobble in the eye
   occipital lobe the rear part of the cerebrum
   opercularization The failure  of the operculum (like a lid) to cover the sylvian fissure. Operculum(noun): any of several parts of the cerebrum bordering the sylvian fissure and concealing the insula
   -otomy cut into
    pachygyria a brain showing abnormally large convolutions or folds (gyri)
     palpebral fissures eyelid fissure
     parietal lobe the mid upper part of the cerebrum
     perisylvian region a region near the sylvian fissure
     perivascular spaces spaces around blood vessels
    phenotype a set of observable characteristics of an individual or group resulting from the interaction of its genotype with its environment.
    philtrum the vertical groove on the median line of the upper lip
    Platelet-activating factor (PAF) a sub-unit of the LIS1 gene
     polyhydramnios excessive amount of amniotic fluid
   polydactyly more fingers or toes than normal
     polymicrogyria (PMG) a cortical malformation in which the cortex has many small gyri.  There are different varieties (or syndromes) of PMG:
  • Bilateral diffuse PMG (spares occipital pole)
  • Bilateral frontal PMG (BFP)
  • Bilateral perisylvian PMG (BPP)
  • Bilateral parieto-occipital PMG (BPOP)
  • Bilateral mesial occipital PMG (BMOP)
     ptosis prolapse of an organ -  drooping of the upper eyelid from paralysis
    pyramidal cells cells found in the cortex of the brain
     pyramidal signs spasticity and paralysis of body muscles. The word pyramidal refers to the "pyramidal tract", which is the main pathway from the brain to the spinal cord to the muscles that controls fine movements.
   recessive (autosomal -) two copies (one from the mother, one from the father) must be mutant to get the disease. (see dominant)
   RELN gene that is implicated in Lissencephaly with Cerebellar Hypoplasia (b).  Located at 7q22
   ring chromosome an abnormal chromosome caused by a break  in both arms of the chromosome, the ends of which unite leading to the formation of a ring.
   scolios a lateral curvature of the spine
  seizure disordered electrical activity in the brain which usually results in temporary loss of conciousness
     sequencing (DNA -) testing which looks at the finest details of a chromosome or gene
  status epilecticus patient does not regain conciousness between seizure attacks
  strabismus deviation of the eye which the patient cannot overcome
  subcortical band heterotopia (SBH) an X-linked disorder more often found in females and is a milder form of lissencephaly.  Also known as 'double cortex' (DC) syndrome
  subcortical laminar heterotopia (SCLH) See subcortical band heterotopia
  sulci grooves on the surface (cortex) of the brain
  sylvian fissure a major groove on the outer sides of the cerebrum
  syndrome a group of concurrent symptoms of a disease
  syndactyly joined fingers or toes (webbed)
  telomeric near to the telomere (the end of a chromosome arm)
  temporal hollowing a narrowing of the head at the temples
  tonic clonic seizures loss of consciousness with generalised convulsions (also known as grand mal)
  translocation one part of a chromosome is swapped over with another part of a chromosome
   type I and II lissencephaly old terminology, I = Classical Lissencephaly, II = Cobblestone Lissencephaly, (WWS/MEB)
  ventricle a hollow area in the brain containing fluid
     Walker-Warburg syndrome a disorder which shows lissencephaly, malformations of the back portion of the brain (cerebellum), abnormalities of the retina of the eye, and progressive degeneration and weakness of the voluntary muscles (congenital muscular dystrophy) and, in some cases, encephalocele.
    white matter cellular material lying beneath the cortex that provides communications between parts of the brain (composed of myelinated and unmyelinated axons)
  X linked a genetic defect that is associated with the X chromosome
    XLIS see DCX

Still stuck for an answer?  Try here for a complete neurological glossary.

Try here for a Seizure Glossary

Try here for a general medical glossary.


Abbreviation Meaning
CSF cerebrospinal fluid (clear fluid that surrounds the brain and
spinal cord)
DSM Diagnostic and Statistical Manual for Mental Disorders (This is the reference that defines the criteria for diagnosing disorders such as Autism, etc)
ILS Isolated Lissencephaly Sequence
LCH Lissencephaly with Cerebellum Hypoplasia or Cerebro-Cellular Lissencephaly
LGS Lennox-Gastaut Syndrome
MDS Miller-Dieker Syndrome
MEB Muscle-Eye-Brain Disease (also the name of the MEB gene)
MLIS Microlissencephaly
MSG Microcephaly with Simplified Gyral Pattern or Microgyrencephaly
NRS Norman-Roberts Syndrome
PMG Polymicrogyria
PLS Partial Lissencephaly Sequence (obsolete term)
SCH Schizencephaly
SBH Subcortical Band Heterotopia
WWS Walker-Warburg Syndrome
XLAG X-linked lissencephaly with ambiguous genitalia


Correct an entry or add a new entry here.  I will add it to the glossary as soon as I can. Please leave your Email address as well - thanks.

Last updated: 07 January 2002 20:19:44