Miller-Dieker syndrome
Overview
Miller-Dieker syndrome (MDS) is a rare genetic disorder. Its signs and symptoms include severe abnormalities in brain development as well as characteristic facial features. Additional birth defects may also be present. MDS was named for the two physicians, J. Miller and H. Dieker who independently described the condition in the 1960s. The hallmark of MDS is lissencephaly (smooth brain), a condition in which the outer layer of the brain, the cerebral cortex, is abnormally thick and lacks the normal convolutions (gyri). In some areas of the brain, gyri are fewer in number but wider than normal (pachygyri). Other areas lack gyri entirely (agyri). Normally, during the third and fourth months of pregnancy, the brain cells in the baby multiply and move to the surface of the brain to form the cortex. Lissencephaly is caused by a failure of this nerve cell migration. MDS is often called Miller-Dieker
Symptoms
Infants with MDS are usually small at birth. Characteristic facial features may include a high forehead with furrows and vertical ridges, indentation of the temples, a small, upturned nose, up-slanting eyes, a small mouth, a thick, broad upper lip with a thin border, low-set ears, and occasionally, a cleft palate. Some infants with MDS also have birth defects involving the heart and kidneys. Signs and symptoms can vary among MDS patients. This may relate to the actual size or exact location of the chromosome 17 deletion in that individual. MDS infants have a very limited capacity for development due to the lissencephaly and associated brain abnormalities. Mental retardation is severe to profound. Infants with MDS may be able to do little more than roll over. Convulsions (seizures) develop within a few weeks of birth and can be severe. Most newborns with MDS have low muscle tone (hypotonia), but later develop stiffness (spasticity) and an arching of the body (opisthotonos). Poor feeding leads to a failure to thrive and increases the risk of pneumonia because the infants can accidentally inhale baby formula into their lungs. Head size is usually in the normal range at birth, but poor brain growth means that, by the age of one year, the children have a smaller-than-normal head size (microcephaly).
Diagnosis
MDS is not the only disorder associated with lissencephaly. Autosomal dominant, autosomal recessive, and X-linked patterns of inheritance have been described among the more than two dozen genetic syndromes featuring this brain abnormality. Less commonly, lissencephaly can also be the result of fetal infections such as prenatal cytolomegalovirus (CMV). An accurate diagnosis of MDS is important not only because it can provide a prognosis for the affected child, but because it can give parents an estimate of their risk for having another child with MDS. MDS may be suspected in the newborn period if an infant has the characteristic facial features along with low muscle tone. Studies of the infant's brain by CAT scan or MRI will show the smooth brain surface. After the diagnosis of MDS is made on the basis of these signs and symptoms, it is very important to study the infant's chromosomes to check for the characteristic chromosome 17 deletion. This is done by sending a small sample of the infant's blood to a cytogenetics laboratory. Trained laboratory personnel (cytogeneticists) first examine the infant's chromosomes through the microscope using traditional techniques. If no deletion or other chromosome rearrangement is detected in this step, newer methods can be used to search for deletions that are too small to see by ordinary means (micro-deletions). A special technique called FISH (fluorescent in situ hybridization) can detect chromosome regions where very small pieces of DNA are missing. This test is usually done on the same blood sample.
Prognosis
Death often occurs in the first three months of life and most infants with MDS die by two years of age, although there have been reports of individuals living for several years.
Treatment
There is no cure for MDS and treatment is usually directed toward comfort measures. Because of the feeding problems and risk of pneumonia, surgeons often place a tube between the stomach and the outside of the abdomen (gastrostomy tube). Feedings can be made through the tube. Seizures are often difficult to control even with medication.