Agenesis of the corpus callosum (ACC) is a brain disorder in which the tissue that connects the left and right sides of the brain (its hemispheres) is partially or completely missing. It is caused by a disruption of brain cell migration during fetal development.

ACC can occur as an isolated condition or in combination with other cerebral abnormalities, including Chiari malformations, Dandy-Walker syndrome, schizencephaly, and holoprosencephaly. ACC can also be associated with malformations in other parts of the body, such as midline facial defects. The effects of the disorder range from subtle or mild to severe, depending on associated brain abnormalities. Children with the most severe brain malformations may have:

• Intellectual impairment
• Seizures
• Hydrocephalus
• Spasticity

People who have a disorder of the corpus callosum typically have:

• Delays in attaining developmental milestones such as walking, talking, or reading
• Clumsiness and poor motor coordination particularly with skills that require coordination of left and right hands and feet, such as swimming, bicycle riding, and driving
• Problems with mental and social processing
• Impairment in social interaction and communication that may overlap with autism spectrum disorder behaviors and typically become apparent between adolescence and adulthood

Females may have a gender-specific condition called Aicardi syndrome, which causes severe cognitive impairment and developmental delays, seizures, abnormalities in the vertebra of the spine, and lesions on the retina of the eye.

Other disorders of the corpus callosum include dysgenesis, in which the corpus callosum is developed in a malformed or incomplete way, and hypoplasia, in which the corpus callosum is thinner than usual. Individuals with these disorders have a higher risk of hearing problems and cardiac abnormalities.

Treatment for ACC usually involves management of symptoms and seizures. It is estimated that at least one in 4,000 individuals has a disorder of the corpus callosum.

During embryonic development, the right and left maxilla bones come together at the midline to form the upper jaw. At the same time, the muscle and skin overlying these bones join together to form the upper lip. Inside the mouth, the palatine processes of the maxilla bones, along with the horizontal plates of the right and left palatine bones, join together to form the hard palate. If an error occurs in these developmental processes, a birth defect of cleft lip or cleft palate may result.

Cleft lip is a common development defect that affects approximately 1:1000 births, most of which are male. This defect involves a partial or complete failure of the right and left portions of the upper lip to fuse together, leaving a cleft (gap).

A more severe developmental defect is cleft palate, which affects the hard palate. The hard palate is the bony structure that separates the nasal cavity from the oral cavity. It is formed during embryonic development by the midline fusion of the horizontal plates from the right and left palatine bones and the palatine processes of the maxilla bones. Cleft palate affects approximately 1:2500 births and is more common in females. It results from a failure of the two halves of the hard palate to completely come together and fuse at the midline, thus leaving a gap between them. This gap allows for communication between the nasal and oral cavities. In severe cases, the bony gap continues into the anterior upper jaw where the alveolar processes of the maxilla bones also do not properly join together above the front teeth. If this occurs, a cleft lip will also be seen. Because of the communication between the oral and nasal cavities, a cleft palate makes it very difficult for an infant to generate the suckling needed for nursing, thus leaving the infant at risk for malnutrition. Surgical repair is required to correct cleft palate defects.

Congenital chloride diarrhea (CCD) is a lifelong condition that causes large, watery stools (diarrhea) that contain an excess of chloride. Those with CCD have diarrhea even before birth. Signs of CCD before birth may be detected with an ultrasound, and may include an increased amount of amniotic fluid (polyhydramnios) and enlarged (dilated) intestinal loops in the fetus. Newborns with CCD are often premature and may have a swollen-looking abdomen (abdominal distention). For this reason, CCD is sometimes first mistaken for an intestinal obstruction. CCD causes electrolyte imbalances including low blood sodium levels (hyponatremia) and chloride levels (hypochloremia). Electrolyte imbalances and severe dehydration can lead to volume depletion (too little fluid surrounding body cells), loss of acid from the blood (metabolic alkalosis), hyperaldosteronism, delayed growth and development, and kidney damage (nephropathy). Untreated CCD can ultimately be fatal within the first weeks or months of life.

Fetal akinesia deformation sequence (FADS) is a condition characterized by decreased fetal movement (fetal akinesia) as well as intra-uterine growth restriction (IUGR), multiple joint contractures (arthrogryposis), facial anomalies, underdevelopment of the lungs (pulmonary hypoplasia) and other developmental abnormalities. It is generally accepted that this condition is not a true diagnosis or a specific syndrome, but rather a description of a group of abnormalities resulting from fetal akinesia.

About 30% of affected individuals are stillborn; many liveborn infants survive only a short time due to complications of pulmonary hypoplasia. FADS may be inherited in an autosomal recessive manner in some cases and may sometimes be caused by mutations in the RAPSN or DOK7 genes.

Fetal cystic hygroma is a congenital malformation of the lymphatic system. The lymphatic system is a network of vessels that maintains fluids in the blood, as well as transports fats and immune system cells. Cystic hygromas are single or multiple cysts found mostly in the neck region. In the fetus, a cystic hygroma can progress to hydrops (an excess amount of fluid in the body) and eventually lead to fetal death. Some cases resolve leading to webbed neck, edema (swelling), and a lymphangioma (a benign yellowish-tan tumor on the skin composed of swollen lymph vessels). In other instances, the hygroma can progress in size to become larger than the fetus. Cystic hygromas can be classified as septated (multiloculated) or nonseptated (simple).

Cystic hygromas can occur as an isolated finding or in association with other birth defects as part of a syndrome (chromosomal abnormalities or syndromes caused by genemutations). They may result from environmental factors (maternal virus infection or alcohol abuse during pregnancy), genetic factors, or unknown factors. The majority of prenatally diagnosed cystic hygromas are associated with Turner syndrome or other chromosomal abnormalities like trisomy 21. Isolated cystic hygroma can be inherited as an autosomal recessive disorder.

Fetal cystic hygroma have being treated with OK-432, a lyophilized mixture of Group A Streptococcus pyogenes and benzyl penicillin, and with serial thoracocentesis plus paracentesis.

Fetal and neonatal alloimmune thrombocytopenia (NAIT) is a blood disorder that affects pregnant women and their babies. NAIT was first reported in the literature in 1953 and is estimated to occur in as many as 1 in 1200 live births. NAIT results in the destruction of platelets in the fetus or infant due to a mismatch between the mother's platelets and those of the baby. Certain molecules (antigens) on the surface of the baby's platelets are recognized as foreign by the mother's immune system. The mother's immune system then creates antibodies that attack and destroy the baby's platelets. Though NAIT can occur whenever the mother's blood mixes with that of the baby, it is usually triggered when the mother is exposed to the baby's blood during delivery. Many cases of NAIT are mild. Signs and symptoms may include a low platelet count (thrombocytopenia) and signs of bleeding into the skin such as petechiae and purpura. In the most severe cases, NAIT can cause bleeding episodes that may result in death or long-term disability. Bleeding episodes can occur either during pregnancy or after birth.

Hydrops fetalis is a serious condition in which abnormal amounts of fluid build up in two or more body areas of a fetus or newborn. There are two types of Hydrops fetalis: immune and nonimmune. Immune Hydrops fetalis is a complication of a severe form of Rh incompatibility. Rh compatibility causes massive red blood cell destruction, which leads to several problems, including total body swelling. Severe swelling can interfere with how the body organs work. Nonimmune Hydrops fetalis occurs when a disease or medical condition disrupts the body's ability to manage fluid. There are three main causes for this type: heart or lung problems, severe anemia (thalassemia), and genetic defects, including Turner syndrome. The exact cause depends on which form a baby has.

Spina bifida is a type of neural tube defect in which the neural tube (the structure in an embryo that becomes the brain and spinal cord) does not completely close during development in the womb. This may result in part of the spinal cord sticking out through an opening in the spine, leading to permanent nerve damage. Babies born with spina bifida often have a fluid-filled sac, covered by skin, on their back. This is called a meningocele. If the sac contains part of the spinal cord and its protective covering, it is known as a myelomeningocele. The signs and symptoms of spina bifida can range from mild to severe, depending on the location and extent of spinal cord involvement. Possible symptoms include include a loss of feeling below the level of the opening, weakness or paralysis of the feet or legs, problems with bladder and bowel control, hydrocephalus, and learning problems.

The cause in most cases is multifactorial, which means that both genetic and environmental factors interact to cause spina bifida. Some cases may be due to the inheritance of specific genemutations, chromosome abnormalities, or fetal exposure to teratogens. Maternal folate deficiency increases the risk to have a baby with spina bifida, and women who take folic acid supplements before and during early pregnancy are much less likely to have a baby with spina bifida.

Treatment typically involves antibiotics, sac closure, and ventriculoperitoneal shunting, usually shortly after birth. Long-term physical, occupational, and/or speech therapy may be needed. In some cases, the condition is life-threatening and is not treatable.

There is also a milder form of the condition called spina bifida occulta in which the nerves develop normally and health problems rarely occur.