Comprehensive study of 28 individuals with SIN3A-related disorder underscoring the associated mild cognitive and distinctive facial phenotype.

Witteveen-Kolk syndrome (OMIM 613406) is a recently defined neurodevelopmental syndrome caused by heterozygous loss-of-function variants in SIN3A. We define the clinical and neurodevelopmental phenotypes related to SIN3A-haploinsufficiency in 28 unreported patients. Patients with SIN3A variants adversely affecting protein function have mild intellectual disability, growth and feeding difficulties. Involvement of a multidisciplinary team including a geneticist, paediatrician and neurologist should be considered in managing these patients. Patients described here were identified through a combination of clinical evaluation and gene matching strategies (GeneMatcher and Decipher). All patients consented to participate in this study. Mean age of this cohort was 8.2 years (17 males, 11 females). Out of 16 patients ≥ 8 years old assessed, eight (50%) had mild intellectual disability (ID), four had moderate ID (22%), and one had severe ID (6%). Four (25%) did not have any cognitive impairment. Other neurological symptoms such as seizures (4/28) and hypotonia (12/28) were common. Behaviour problems were reported in a minority. In patients ≥2 years, three were diagnosed with Autism Spectrum Disorder (ASD) and four with Attention Deficit Hyperactivity Disorder (ADHD). We report 27 novel variants and one previously reported variant. 24 were truncating variants; three were missense variants and one large in-frame gain including exons 10-12.

Further delineation of the phenotype of chromosome 14q13 deletions: (positional) involvement of FOXG1 appears the main determinant of phenotype severity, with no evidence for a holoprosencephaly locus.

BACKGROUND: Deletions including chromosome 14 band q13 have been linked to variable phenotypes. With current molecular methods the authors aim to elucidate a genotype-phenotype correlation by accurately determining the size and location of the deletions and the associated phenotype. METHODS: Here the authors report the molecular karyotyping and phenotypic description of seven patients with overlapping deletions including chromosome 14q13. RESULTS: The authors show that deletions including 14q13 result in a recognisable phenotype mainly due to haploinsufficiency of two genes (NKX2-1, PAX9). FOXG1 (on chromosome band 14q12) involvement seems to be the main determinant of phenotype severity. The patients in this study without FOXG1 involvement and deletions of up to 10 Mb have a relatively mild phenotype. The authors cannot explain why some patients in literature with overlapping but smaller deletions appear to have a more severe phenotype. A previously presumed association with holoprosencephaly could not be confirmed as none of the patients in this series had holoprosencephaly. CONCLUSIONS: FOXG1 appears the main determinant of the severity of phenotypes resulting from deletions including 14q13. The collected data show no evidence for a locus for holoprosencephaly in the 14q13 region, but a locus for agenesis of the corpus callosum cannot be excluded.