The severity and localization of disease presentation is dependent on the timing and stage of tooth development in which the defective enamel formation occurred. Hereditary causes of enamel hypoplasia include:

Primary abnormalities in enamel development, such as amelogenesis imperfecta
Certain dermatological conditions, such as Ehlers-Danlos syndrome
Other complex hereditary conditions such as Usher syndrome, Seckel syndrome, Treacher-Collins syndrome, Heimler syndrome & Ellis-Van Creveld syndromeEnvironmental causes of enamel hypoplasia include:

Nutritional deficits, such as Vitamin D, iron or calcium deficiency
Birth injury or preterm birth
Smoking during pregnancy
Trauma
Radiation
Certain infections (e.g. congenital syphilis, cytomegalovirus, congenital rubella)
Certain diseases (such as undiagnosed and untreated celiac disease, chicken pox, congenital syphilis)
High fever
Hypoxia (i.e. from severe cardiac defect)
Excessive fluoride exposure (dental fluorosis)
Tetracycline
Vitamin A, C, or D deficiency

Clinical relevance
Enamel hypoplasia is a risk factor for dental caries in children including early childhood caries (ECC), which continues to be a burden for many children. This association has been identified as significant and independent, and is believed that the formation of pits and missing enamel provides a suitable local environment for adhesion and colonization of cariogenic bacteria. Historically, enamel hypoplasia has been under-appreciated as a risk factor for ECC. Developmental defects in enamel that affect tooth appearance in the esthetic zone (i.e. upper front teeth) may cause individuals to experience social embarrassment or anxiety regarding the appearance of their teeth. Guidelines for Treatment of Enamel Hypoplasia
Dental sealants may be indicated for the prevention of caries in hypoplastic pit & fissure systems.
Enamel hypoplasia is a defect of the teeth in which the enamel is deficient in quantity, caused by defective enamel matrix formation during enamel development, as a result of inherited and acquired systemic condition(s). It can be identified as missing tooth structure and may manifest as pits or grooves in the crown of the affected teeth, and in extreme cases, some portions of the crown of the tooth may have no enamel, exposing the dentin. It may be generalized across the dentition or localized to a few teeth. Defects are categorized by shape or location. Common categories are pit-form, plane-form, linear-form, and localised enamel hypoplasia. Hypoplastic lesions are found in areas of the teeth where the enamel was being actively formed during a systemic or local disturbance. Since the formation of enamel extends over a long period of time, defects may be confined to one well-defined area of the affected teeth. Knowledge of chronological development of deciduous and permanent teeth makes it possible to determine the approximate time at which the developmental disturbance occurred. Enamel hypoplasia varies substantially among populations and can be used to infer health and behavioural impacts from the past. Defects have also been found in a variety of non-human animals. Causes
Enamel hypoplasia is believed to result from the dysfunction of ameloblasts—enamel-producing cells—either for a short period of time or throughout their lifespan. Enamel hypoplasia has a wide variety of known causes. Some causes are hereditary and others are from environmental exposure.