Microcephaly: general considerations and aids to nosology.

Area of Science:

• Medical Genetics
• Developmental Biology
• Pediatrics

Background:

• Microcephaly is defined by occipito-frontal head circumference (OFC) below established norms, adjusted for age, sex, and parental OFC.
• Distinguishes between "relative" microcephaly (small head, small child) with better prognosis and "absolute" microcephaly.
• Classifies microcephaly as "primary" (abnormal at birth) or "secondary" (acquired postnatally due to various insults).

Purpose of the Study:

• To explore the complex nosology of syndromal and non-syndromal microcephaly.
• To illustrate the challenges in classifying microcephaly due to overlapping manifestations and pleiotropy.
• To highlight the utility of specialized databases in understanding microcephaly.

Main Methods:

• Utilized standard definitions for microcephaly, including occipito-frontal circumference (OFC) measurements and adjustments.
• Reviewed literature and case examples of syndromal microcephaly associated with normal or abnormal intelligence.
• Employed specialized resources such as McKusick's Catalog of Mendelian Inheritance in Man (MIM) and electronic databases (OMIM, POSSUM, SYNDROME, MEDLINE).

Main Results:

• Some syndromal microcephaly cases, including "primordial dwarfs" and certain genetic syndromes, can present with normal intelligence.
• The diagnostic classification of microcephaly is complicated by pleiotropy and overlapping clinical features.
• Electronic databases significantly aid in navigating the complexity of microcephaly nosology.

Conclusions:

• The classification of microcephaly is intricate, demanding sophisticated diagnostic approaches.
• Understanding the genetic and developmental basis of microcephaly is crucial for accurate diagnosis and prognosis.
• Advanced information retrieval tools are essential for comprehensive study of microcephaly.