Glossary
There are currently 86 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
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, 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
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
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 foramen ovale
hole between the left and right atria (upper chambers) of the heart that did not close before birth
Pena-Shokeir syndrome
autosomal recessive non-aneuploidic condition with some clinical features similar to that of trisomy 18; most often it is lethal
Penetrance
the extent to which a particular gene or set of genes is expressed in the phenotypes of individuals carrying it, measured by the proportion of carriers showing the characteristic phenotype
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 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
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
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
Pierre Robin complex
congenital anomaly characterized by an unusually small lower jaw (micrognathia), downward displacement of the tongue (glossoptosis), and occasionally, cleft palate
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
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, 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
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
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
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
Psycho-motor development
Of or relating to movement or muscular activity associated with mental processes
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
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
Pyloric stenosis
abnormal narrowing of the valve at the outlet from the stomach, preventing normal passage of food into the small intestine