Genetic and Medical Glossary

Glossary

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There are 85 names in this directory beginning with the letter P.
p arm
short region of a chromosome attached to the centromere at the top end and the telomere at the other; contains bands of genes numbered from the centromere out

Pachygiria
unusually thick convolutions of the cerebral cortex

Palate, Hard, Short
distance between the labial point of the incisive papilla to the midline junction of the hard and soft palate more than 2 SD below the mean; decreased length of the hard palate

Palate, high
height of the palate more than 2 SD above the mean; palatal height at the level of the first permanent molar more than twice the height of the teeth

Palate, submucous cleft
soft palatal defect with intact overlying mucosa comprising two of the following three findings: (1) notching of the posterior border of the hard palate, (2) bifid uvula, or (3) muscular diastasis leading to a midline translucent zone or furrow in the soft palate

Pallister-Killian syndrome (Tetrasomy 12p)
chromosomal disorder caused by the presence of four copies of the short arm of chromosome 12; symptoms may include a coarse face with a high forehead, sparse hair on the scalp, an abnormally wide space between the eyes, a fold of the skin over the inner corner of the eyes, a broad nasal bridge with a highly arched palate, and streaks of skin lacking color; intellectual impairment and loss of muscle tone are common

Palmar crease, absent
absence of a major crease of the palm (distal transverse crease, proximal transverse crease, or thenar crease)

Palpebral fissure
scaphoid space or outline formed by eyelid margins when the eye is open

Palpebral fissure, down-slanted
inclination is more than 2 SD below the mean for age

Palpebral fissure, up-slanted
inclination is more than 2 SD above the mean for age; may be associated with microcephaly

Pancytopenia
abnormal reduction in the number of red blood cells, white blood cells, and blood platelets in the blood

Paracentric inversion
an inversion of a chromosome’s sequence that does not involve the centromere, taking place on a single arm of the chromosome

Paranoia
unfounded or exaggerated distrust of others, sometimes reaching delusional proportions

Parenchyma
essential or functional elements of an organ

Parietal foramina
inconstant foramen in the parietal bone occasionally found bilaterally near the sagittal margin posteriorly; when present it transmits an emissary vein to the superior sagittal sinus

Paroxysm
sudden attack or increase of symptoms of a disease

Partial trisomy
occurs when only a part of a chromosome attaches to another

Patau syndrome (trisomy 13)
genetic disorder in which there is an extra copy of chromosome 13; generally causes malformed, low set ears, severe intellectual impairment, kidney and heart defects, and microcephaly. Mortality is high

Patent ductus arteriosus
congenital heart in which the ductus arteriosus does not close

Patent foramen ovale
hole between the left and right atria (upper chambers) of the heart that did not close before birth

Pathologic
altered or caused by disease; indicative of disease

Pectus carinatum
protrusion of the sternum

Pectus excavatum
inward malformation of the sternum

Pedigree
diagrammatic representation of a family health history or family health tree

Pena-Shokeir syndrome
autosomal recessive non-aneuploidic condition with some clinical features similar to that of trisomy 18; most often it is lethal

Pericentric inversion
an inversion of a chromosome’s sequence involving the centromere

Periventricular heterotopia
brain malformation, due to abnormal neuronal migration, in which a subset of neurons fails to migrate into the developing cerebral cortex and remains as nodules that line the ventricular surface; X-linked dominant disorder mapped to FLN1gene; females display borderline mental retardation, epilepsy of variable severity, and extra-central nervous system signs, especially cardiovascular defects or coagulopathy

Pes cavus
presence of an unusually high plantar arch

Pes Planus (flat feet)
arch of the foot is in contact with the ground or floor when the individual is standing

Peters’ anomaly
congenital eye disorder in which development of the anterior segment is abnormal, leading to incomplete separation of the cornea from the iris or the lens

Peutz–Jeghers syndrome
autosomal dominant genetic condition characterized by multiple benign polyps called hamartomas on the mucous lining in the gastrointestinal system and dark skin discolorations, especially around the eyes, nostrils, mucous membranes of the mouth, perianal area, and inside the mouth

Phalange
bones of the fingers and toes

Phelan–McDermid syndrome
chromosomal disorder in which a portion of the long arm (q) of chromosome 22 is missing; characterized by low muscle tone, normal to accelerated growth, absent to severely delayed speech, moderate to profound intellectual impairment, and minor dysmorphic features

Phenotype
the physical appearance or biochemical and physiological characteristics of an individual, which is determined by both heredity and environment

Philtral ridges, malaligned
absence of the usual parallel position of philtral ridges

Philtrum
vertical groove in the midline portion of the upper lip bordered by two lateral ridges or pillars

Philtrum, deep
accentuated, prominent philtral ridges giving rise to an exaggerated groove in the midline between the nasal base and upper vermillion border

Philtrum, long
distance between nasal base and midline upper lip vermilion border more than 2 SD above the mean; increased distance between nasal base and midline upper lip vermilion border; length of philtrum usually shows accompanied by a short nose

Phonophobia
persistent, abnormal, and unwarranted fear of sound

Piebaldism
Patchy absence of the pigment of scalp hair, giving a streaked appearance

Pierre Robin complex
congenital anomaly characterized by an unusually small lower jaw (micrognathia), downward displacement of the tongue (glossoptosis), and occasionally, cleft palate

Pinna
part of the ear that projects like a little wing from the head

Pitt–Hopkins syndrome
characterized by severe intellectual disability and developmental delay, breathing problems, recurrent seizures (epilepsy), and distinctive facial features and caused by mutations in the TCF4 gene on chromosome 18 at 18q21.1

Plagiocephaly
asymmetric head shape, which is usually a combination of unilateral occipital flattening with ipsilateral frontal prominence, leading to a rhomboid cranial shape

Politelia
presence of supernumerary (extra) nipples

Polycystic Kidney Disease
autosomal recessive genetic disorder caused by mutations of the PKHD1 gene located on chromosome 16 at 16p13.3 and characterized by the formation of fluid-filled sacs (cysts) in the kidneys; additional organ systems may be affected, especially the liver; high blood pressure (hypertension), excessive thirst, frequent urination and feeding difficulties may also occur

Polydactyly
a genetic disorder where the embryo develops extra fingers or toes

Polydactyly, mesoaxial
presence of a supernumerary finger or toe (not a thumb or hallux) involving the third or fourth metacarpal/tarsal with associated osseous syndactyly

Polydactyly, Mirror Image
hand or foot with more than five digits that has a recognizable A/P axis of symmetry

Polymicrogyria
developmental anomaly of the brain marked by development of numerous small convolutions (microgyri), causing cognitive impairment

Polymorphism
the presence of many different alleles for a particular locus in individuals of the same species

Polyploid
a cell or organism that possesses multiple sets of chromosomes

Polyposis
condition characterized by the presence of numerous polyps

Postaxial
pertaining to or situated behind the axis of the body, especially the posterior side

Postaxial polydactyly of the foot
presence of a supernumerary digit that is not a hallux (big toe)

Posterior
toward the back or denoting the back surface of the body

Posterior embryotoxon
ring-like opacity at the margin of the cornea in the eye

Potocki-Lupski syndrome
caused by duplication on chromosome 17p11.2; wide range of developmental and motor issues; strong association with Charcot-Marie-Tooth disease

Potocki–Shaffer syndrome
disorder that affecting development of the bones, brain, and other organs, characterized by the growth of exostoses, enlarged parietal foramina, intellectual disability, delayed development of speech, motor and social skills, and distinctive facial features; caused by deletions on the short (p) arm of chromosome 11 at 11p11.2

Potter sequence
kidneys fail to develop properly, causing lack of amniotic fluid (oligohydramnios) that, in turn causes pressure of the uterine wall which leads to an unusual facial appearance and stops development of the lungs; can also lead to abnormal limbs

Prader–Willi syndrome
imprinting chromosomal disorder caused by mutation of chromosome 15 in the region of 15q11.2-q13 on the paternal side (mutation of this region on the maternal side causes Angelman syndrome); characterized by low muscle tone and poor feeding in infancy and an insatiable appetite as the child grows; varying degrees of cognitive impairment are common

Preauricular pits
Small indentation in front of the ear opening

Preaxial
Situated in front of or superior to the median axis of the body or a body part

Preaxial polydactyly of the hand
Duplication of all or part of the first ray

Prenatal hypoplasia
low birth weight when born at term

Prenatal testing
testing that is done during pregnancy to examine the chromosomes or genes of a fetus to detect the presence or absence of a genetic disorder

Prevalence
the percentage of people in a given population that are affected by a disorder at that particular time

Proband
affected person whose disorder, or concern about the disorder, brings a family or pedigree to be genetically evaluated

Proboscis
fleshy, tube-like structure usually located in the midline of the face or just to one side of the midline; has a single cavity and may be found in association with a malformed nose and absence of one or both nares

Propositus
the individual in a human pedigree who is the focus of the pedigree, usually by being the first person who came to the attention of the geneticist

Prosencephalon
another term for forebrain

Protein
a biological molecule composed of amino acids linked together by peptide bonds; used as structural components of the cell or as enzymes; the term “protein” can refer to a single chain of amino acids or to multiple chains of amino acids functioning in a concerted way

Proximal
situated nearer to the center of the body or the point of attachment

Psycho-motor development
Of or relating to movement or muscular activity associated with mental processes

Pterygia
wing–like triangular membrane between the torso and upper arm in the armpit area

Pterygium colli
redundant neck skin

Ptosis
upper eyelid lid margin is positioned 3mm or more lower than usual and covers the superior portion of the iris; upper lid margin obscures at least part of the pupil; reduction in eyelid opening that is not fixed but can be increased actively or passively

Pubertas praecox
Sexual development before the age of eight in girls, and age 10 in boys

Pulmonary hypoplasia
incomplete development of the lungs, resulting in an abnormally low number or size of bronchopulmonary segments or alveoli

Pulmonary stenosis
condition in which the pulmonary valve is too tight, so that the flow of blood from the right ventricle of the heart into the pulmonary artery is impeded

Purine
either of the nitrogenous bases adenine or guanine; used in the structure of nucleic acids

Pyelocalyceal
Relating to the renal pelvis and calices

Pyeloectasis
dilation of the renal pelvis

Pyloric stenosis
abnormal narrowing of the valve at the outlet from the stomach, preventing normal passage of food into the small intestine

Pyrimidine
any of the nitrogenous bases cytosine, thymine, or uracil; used in the structure of nucleic acids

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