A functional motor deficit where individuals whose responses to the challenges of exercise fail to achieve levels considered normal for their age and gender.

Abnormal protrusion of the scapula away from the surface of the back.

A deficiency or slowing down of growth pre- and postnatally.

Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm.

A condition of diminution or cessation of secretion of one or more hormones from the anterior pituitary gland. This may result from surgical or radiation ablation, non-secretory pituitary neoplasms, metastatic tumors, infarction, pituitary apoplexy, infiltrative or granulomatous processes, and other conditions.

Intellectual disability, previously referred to as mental retardation, is characterized by subnormal intellectual functioning that occurs during the developmental period. It is defined by an IQ score below 70.

A type of anemia characterized by an abnormally low concentration of hemoglobin in the erythrocytes.

Sideroblastic anemia results from a defect in the incorporation of iron into the heme molecule. A sideroblast is an erythroblast that has stainable deposits of iron in cytoplasm (this can be demonstrated by Prussian blue staining).

Increased count of erythroid precursor cells, that is, erythroid lineage cells in the bone marrow.

A type of erythrocyte inclusion characterized by basophilic stippling of erythrocytes, that is, by numerous very small coarse or fine blue granules within the cytoplasm with the additional stipulation that the stippled particles are due to iron granules (demonstrable by the Prussian blue stain).

A kind of anemia in which the volume of the red blood cells is reduced.

Abnormally increased curvature (anterior concavity) of the lumbar or cervical spine.

Developmental hypoplasia of the mandible.

Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.

Reduced strength of muscles.

A phenomenon whereby patients are not able to stand up without the use of the hands owing to weakness of the proximal muscles of the lower limbs.

Generalized (unlocalized) atrophy affecting muscles of the limbs in both proximal and distal locations.

The capability that a joint (or a group of joints) has to move, passively and/or actively, beyond normal limits along physiological axes.

Generalized muscular hypotonia (abnormally low muscle tone).

An abnormal appearance of muscle fibers observed on muscle biopsy. Ragged red fibers can be visualized with Gomori trichrome staining as irregular and intensely red subsarcolemmal zones, whereas the normal myofibrils are green. The margins of affect fibers appear red and ragged. The ragged-red is due to the accumulation of abnormal mitochondria below the plasma membrane of the muscle fiber, leading to the appearance of a red rim and speckled sarcoplasm.

An abnormally reduced activity of the enzyme cytochrome C oxidase in muscle tissue.

Head circumference below 2 standard deviations below the mean for age and gender.

A functional defect characterized by reduced total lung capacity (TLC) not associated with abnormalities of expiratory airflow or airway resistance. Spirometrically, a restrictive defect is defined as FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity) less than 80 per cent. Restrictive lung disease may be caused by alterations in lung parenchyma or because of a disease of the pleura, chest wall, or neuromuscular apparatus.

An abnormal buildup of lactic acid in the body, leading to acidification of the blood and other bodily fluids.

Increased concentration of ferritin in the blood circulation.

Abnormally increased level of blood lactate (2-hydroxypropanoic acid). Lactate is produced from pyruvate by lactate dehydrogenase during normal metabolism. The terms lactate and lactic acid are often used interchangeably but lactate (the component measured in blood) is strictly a weak base whereas lactic acid is the corresponding acid. Lactic acidosis is often used clinically to describe elevated lactate but should be reserved for cases where there is a corresponding acidosis (pH below 7.35).

Height of the palate more than 2 SD above the mean (objective) or palatal height at the level of the first permanent molar more than twice the height of the teeth (subjective).

Lack of prominence of the nose resulting from a posteriorly-placed nasal ridge.

Abnormally pale skin.

Double rows of eyelashes.

Passing the age when puberty normally occurs with no physical or hormonal signs of the onset of puberty.

Although hypertelorism means an excessive distance between any paired organs (e.g., the nipples), the use of the word has come to be confined to ocular hypertelorism. Hypertelorism occurs as an isolated feature and is also a feature of many syndromes, e.g., Opitz G syndrome (see 300000), Greig cephalopolysyndactyly (175700), and Noonan syndrome (163950) (summary by Cohen et al., 1995).

An abnormality of the retina characterized by pigment deposition. It is typically associated with migration and proliferation of macrophages or retinal pigment epithelial cells into the retina; melanin from these cells causes the pigmentary changes. Pigmentary retinopathy is a common final pathway of many retinal conditions and is often associated with visual loss.

A reduction in the activity of the mitochondrial respiratory chain complex I, which is part of the electron transport chain in mitochondria.

A reduction in the activity of the mitochondrial respiratory chain complex IV, which is part of the electron transport chain in mitochondria.