How to assess causes

A comprehensive history and a careful physical examination are essential for identifying and timing the causative factor(s). In everyday practice it is appropriate to assess the family history, embryological, and postnatal development, possible pathogenetic mechanisms, and the time of the exposure to the supposed agent ( Table.. 1). The finding of more than three minor malformations suggests genetic or early developmental disorder provided that the same dysmorphic features are not found in close relatives.'29ยป Infants at risk for external prenatal causes, perinatal causes, or postnatally acquired disorders should be examined carefully for dysmorphic features which may indicate alternative or additional cause. The diagnosis usually becomes evident by working out the history and clinical signs. Databases for analyses of dysmorphology, symptoms, or other findings are useful aids in the search of an aetiological diagnosis. (3 ,37)

Ophthalmological and audiological examinations can be arranged and other necessary investigations carried out when suggested by the history and physical examination (Table^).'!,2,5,.! 1,23,2831) If the findings are in accordance with history and a person has no congenital anomalies, further examinations are seldom needed. However, the possibility of a metabolic disorder should be kept in mind, especially as congenital anomalies or dysmorphic features may occur in people with metabolic disorders. Metabolic studies should be performed for every patient with progressive symptoms. If the history and physical findings do not match, or if there are congenital anomalies or more than three minor dysmorphic features, additional studies are needed. (29) Because more accurate diagnostic methods are being developed, it is useful to keep for each person a dated chart of examinations performed. (1Z>

Table 2 Diagnostic examinations of mental retardation

Prenatal diagnosis may be indicated when there is a known parental balanced translocation, chromosomal aberration of a sibling, a known single gene disorder in family, a multifactorial disorder such as neural-tube defect in the family, or the mother is elderly. The development of the fetus can be followed by ultrasound; many structural abnormalities can be seen after 10th to 11th gestation weeks.

The karyotype of a fetus can be identified after 10th week of gestation from a chorionic villus sample, or after 15th week gestation from the cells of amniotic fluid. A known single gene disorder can be searched from the chorionic villus sample or amniotic fluid cells by DNA, enzyme, or other specific methods. Neural-tube defects can be found by the determination of a-fetoprotein from amniotic fluid and by repeated ultrasound examinations from the 12th to 22nd weeks of gestation.

The examination of fetal chromosomes as a form of age-specific screening is based on the significantly increased probability of a Down syndrome child among mothers aged 35 years or older. Other general screening methods for Down syndrome are based on markers such as a-fetoprotein and human chorionic gonadotropin or ultrasound measurement of the neckfold of the fetus. After a positive screening result further examinations are needed before confirming a diagnosis. Prenatal diagnostic methods and identification of parental balanced translocations or aberrations in single gene are increasingly available and preimplantation diagnoses are becoming available for some diseases using only one or two cells. (I,1, ,38,39)

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