Exome sequencing overrides formal genetics: ASPM mutations in a case study of apparent X-linked microcephalic intellectual deficit

To the Editor : Ten years ago we evaluated two brothers with intellectual disability (ID). The 29-year-old brother presented with moderate-severe ID with congenital microcephaly [(occipital-frontal circumference (OFC) 42.5 cm, −7.8 SD; height 182 cm, 75◦–90◦ percentile] (Fig. 1a). He was not able to read but was able to write his name. The younger 20-year-old brother exhibited severe ID, congenital microcephaly (OFC 41 cm, −8.7 SD; height 160 cm, 5◦ percentile) and had a surgically corrected cleft lip and palate (Fig. 1a). He was unable to read or write. Neither patient was able to take care of himself and both exhibited hyperactivity with autoand hetero-aggressive behavior. Brain MRI of the older brother showed a global reduction in brain size, thin brain stem, normal corpus callosum and temporal pachygiria. Cardiac ultrasound of both patients revealed mild tricuspid valve insufficiency in the older brother and mild tricuspid and pulmonary valve insufficiency in the younger. The mother (II-5) and the 26-year-old sister (III-8) had microcephaly (Fig. 1b). Their father died at 40 years of heart failure. Both the mother and the sister reported females with a small head size in the maternal branch of the pedigree (Fig. 1b). In most of these females microcephaly was directly ascertained. The genetic counseling concluded that there was an X-linked semi-dominant disorder and that there was a recurrence risk for ID of up to 50% for male offspring of the sister (III-8). After genetic counseling a number of genetic tests were performed. We first tested a panel of genes involved in X-linked ID (MECP2 , ARX , OPHN1 , FMR2 , NLGN3 , NLGN4 , PQBP1 , RSK2 , AGTR2 ) because the samples were enrolled in the Italian X-linked Mental Retardation Project (http://www. biobank.unisi.it/) (1). In the following years, with the advent of array-CGH technology, the samples were first analyzed with X-specific BAC array-CGH and successively with higher resolution arrays (Agilent 105K, Agilent Technologies, Santa Clara, CA and Affymetrix Genome-Wide Human SNP Array 6.0,