LAUSR

16p11.2 microdeletion syndrome is a recognisable chromosomal anomaly caused by microdeletions in the 16p11.2 locus. It is characterized by developmental delay intellectual disability and social impairments or susceptibility to autism spectrum disorder. It also involves mild variable dysmorphism and predisposition to obesity. Motor skills cognitive function and expressive language are mainly impaired and 20% of affected individuals present with epilepsy. There also appears to be an increase in all types of birth defects particularly vertebral anomalies. Structural abnormalities have also been described in the central nervous system such as Chiari malformation or cerebellar ectopia.1 The estimated prevalence in the general population is 1/5000.2 The inheritance is autosomal dominant although most cases occur as a de novo mutation. The diagnosis is established by chromosomal analysis using molecular methods such as microarray or targeted deletion analysis by fluorescence in situ hybridization (FISH). Clinical suspicion is necessary. This article describes two male probands with this rare genetic defect who presented with diverse clinical phenotypes. It highlights the presence of a new clinical feature hyperinsulinaemic hypoglycaemia that has not been reported before and adds to the variability of this entity. Hyperinsulinaemic hypoglycaemia is one of the common causes of hypoglycaemia in neonates and infancy. It is characterized by hypoketotic hypofattyacidaemic and hyperinsulinaemic hypoglycaemia. Hence it is important to diagnose early and promptly manage in order to avoid hypoglycaemic brain injury. Several different genetic aetiologies have been described in patients with hyperinsulinaemic hypoglucaemia which includes its occurrence in several syndromic disorders (eg Turners Beckwith‐Wiedemann). However for approximately 50% of patients with hyperinsulinaemic hypoglycaemia the underlying genetic mechanism remains unknown.3 It is noteworthy that both patients exhibited hyperinsulinaemic hypoglycaemia soon after birth (Table 1) which was Diazoxide‐responsive and resolved almost a year later.