<prompt> A 9 month infant presents with a head circumference of 39 cm. All of the following can be the underlying causes EXCEPT?Edward syndromeMaternal smokingAlexander diseaseCongenital Toxoplasmosis  <response>: Alexander disease- cause of Megalencephaly. Here, a 9 month infant has HC39cm, so heshe has microcephaly, Normal head circumference at bih 33-35 cm Rate of increase in HC 1st 3 months 2cmmonth Next 3 months 1cmmonth Next 6 months 0.5cmmonth Next 2 years 0.2cmmonth Megalencephaly causes:- Benign familial megalencephaly Most common cause Amino acid disorders Maple syrup urine disease glutaric aciduria Lysosomal storage disorder Weaver syndrome Achondroplasia Neurofibromatosis sotos syndrome Alexander disease Canavan disease Galactosemia The other 3 are causes of microcephaly. At 9 months ; ideally HC should be 43.5-45.5 cm. 