decrease in fear. Hypothalamic dysfunction may also result in problems with feeding, sleep, and body temperature regulation. Feeding behaviors in children with ONH often include hyperphagia (overeating), resulting in obesity; or hypophagia (reduced food intake) with or without weight loss. Children also frequently experience aversion to specific textures of food. Disturbance of circadian sleep rhythm, resulting in abnormal sleep-wake cycles, is noted in one-third of children with ONH. This disturbance could result in behavioral problems and disruption of family life. Development More than 70% of children with ONH experience developmental delay, ranging from isolated focal defects to delay in all areas of development (global delay). Motor delay is most common (75%) and communication delay is least common (44%). Predictors of significantly delayed development include hypoplasia or agenesis of the corpus callosum and hypothyroidism. The absence of the septum pellucidum does not predict developmental delay. Delays may occur in unilateral (39%) as well as bilateral (78%) cases. Cause Genetic risks Mutations of genes involved in transcription regulation, chromatin remodelling, α-dystroglycan glycosylation, cytoskeleton and scaffolding protein, RNA splicing, and the MAP kinase signalling pathway are currently known to cause ONH. Many transcription factors for eye development are also involved in the morphogenesis of forebrain, which may explain why ONH is commonly a part of a syndrome involving brain malformations. ONH impacts all ethnic groups, although in the United States, occurrence is lower in persons of Asian descent. To date, there have been few reports of ONH occurrence in Asian countries, although it is uncertain why this is so. Gestational and exposure history Although many perinatal and prenatal risk factors for ONH have been suggested, the predominant, enduring, most frequent risk factors are young maternal age and primiparity (the affected child being the first child born to the mother). Increased frequency of delivery by caesarean section and fetal/neonatal complications, preterm labor, gestational vaginal bleeding, low maternal weight gain, and weight loss during pregnancy are also associated with ONH. Diagnosis ONH is diagnosed by ophthalmoscopic examination. Patients with ONH exhibit an optic nerve that appears smaller than normal and different in appearance from small optic nerves caused by other eye conditions such as optic (nerve) atrophy. DM:DD ratio has proven to be a clinically useful measurement to help diagnose optic nerve hypoplasia. Where "DM" represents the distance from Disk to Macula, and "DD" represents Disc Diameter. The mean disc diameter (DD) is (Vertical diameter