46,XY differences of sex development (DSD) are conditions with extreme phenotypic and genetic heterogeneity. Therefore, their diagnosis remains a major challenge for both clinicians and geneticists. In this study, we aimed to identify the underlying genetic causes of DSD in a series of 3 Moroccan patients with syndromic 46,XY DSD recruited in the BRO Biobank. Methods: Karyotyping analysis was performed on peripheral blood samples using standard R banding techniques. SRY gene was analyzed using PCR amplification followed by Sanger sequencing. Whole exome sequencing (WES) was performed after unsuccessful conventional genetic analyses. Candidate variants were evaluated by segregation analysis and molecular modeling. WES identified three pathogenic variants in genes encoding various components of the epigenetic machinery: in patient 1, a novel heterozygous frameshift variant c.4072dup (p.Glu1358GlyfsTer29) in the KAT6B gene associated with two clinically distinct syndromes (genitopatellar syndrome and Say-Barber-Biesecker-Young-Simpson syndrome) was detected; in patient 2, we identified a previously reported de novo heterozygous nonsense variant c.12943C>T (p.Gln4315Ter) in KMT2D responsible for Kabuki syndrome; in patient 3, WES revealed a novel heterozygous missense variant c.4056C>G (p.Phe1352Leu) in CHD7 responsible for CHARGE syndrome. We discuss the genotype-phenotype correlation in these syndromic 46,XY DSD and discuss the relevance of the epigenetic genes in sexual development. Our findings highlight the utility of WES in discriminating clinically overlapping syndromic 46,XY DSD to provide an accurate diagnosis, thus allowing better follow-up and appropriate patient management. In addition, our study enriched the mutational spectrum of syndromic 46,XY DSD and confirmed the genotype-phenotype correlations.

1例5月龄男性患儿出现反复呼吸困难5个月，存在全面发育迟缓、喂养困难、肌张力低下、先天性甲状腺功能减退、听视觉功能障碍等表现。检查发现存在上睑下垂，隐睾，胼胝体较薄及肾盂积水；染色体核型为46，X，Y。全外显子组测序分析KAT6B基因NM_012330.4：c.4205_4206del（p.Ser1402Cysfs*5）杂合变异，患儿父母均不携带该变异，属于新发变异，患儿确诊Genitopatellar综合征。.

KAT6B mutations are responsible for Say-Barber-Biesecker-Young-Simpson syndrome or Genitopatellar syndrome, with most mutations occurring in its exon 18. A pregnancy with normal early antenatal examination revealed the presence of hypospadias in the fetus but with no abnormal amniotic fluid volume in ultrasonography at 29th+ 4d weeks' gestation. After amniocentesis, the trios' whole exome sequencing was performed and a novel frameshift mutation (KAT6B: exon10: c.2153_2159del, p. R718Lfs*3) was identified for her fetus, then verified by the parents as a de novo mutation. Following this couple's decision to induce labor, the appearance of the fetus had hypospadias but with a normal face and was able to be palpated for the patella. KAT6B mutations often occur with a variety of symptoms. To our acknowledgment, this is the first report of a novel de novo KAT6B mutation causing only hypospadias for the fetus, which further expands the spectrum of KAT6B variants and the genotype-phenotype relationship for this disease.

Loss of the gene encoding the histone acetyltransferase KAT6B (MYST4/MORF/QKF) causes developmental brain abnormalities as well as behavioral and cognitive defects in mice. In humans, heterozygous variants in the KAT6B gene cause two cognitive disorders, Say-Barber-Biesecker-Young-Simpson syndrome (SBBYSS; OMIM:603736) and genitopatellar syndrome (GTPTS; OMIM:606170). Although the effects of KAT6B homozygous and heterozygous mutations have been documented in humans and mice, KAT6B gain-of-function effects have not been reported. Here, we show that overexpression of the Kat6b gene in mice caused aggression, anxiety, and spontaneous epilepsy. Kat6b overexpression led to an increase in histone H3 lysine 9 acetylation and upregulation of genes driving nervous system development and neuronal differentiation. Kat6b overexpression additionally promoted neural stem cell proliferation and favored neuronal over astrocyte differentiation in vivo and in vitro. Our results suggest that, in addition to loss-of-function alleles, gain-of-function KAT6B alleles may be detrimental for brain development.

Genitopatellar syndrome (GPS) is a rare genetic disorder characterized by a spectrum of clinical manifestations including the absence of patellae, psychomotor retardation, congenital flexion deformity of the lower limbs, and genitourinary abnormalities. A 5-year-old female presented to the Faculty of Dentistry Clinic for a routine dental examination. Physical examination revealed distinctive phenotypic features, notably wide thumbnails and limb wrinkling, while facial appearance appeared within normal limits. At birth, the patient exhibited dysmorphic clubfoot, genital anomalies, bilateral hydronephrosis, and hepatomegaly. Subsequent MRI evaluation disclosed bilateral dysplastic femoral trochlea with lateral patellofemoral dislocation, accompanied by marked tibial rotation and vertical talus. Additionally, bilateral hindfoot valgus deformity and first metatarsophalangeal joint flexion deformity were noted. Molecular analysis using Sanger sequencing identified a de novo heterozygous nonsense mutation (c.4117, p.Glu1373Ter) in the KAT6B gene. Oral examination revealed shortened clinical crowns, absence of caries in the primary teeth, and delayed eruption of the primary canines (Cs) and second molars (Es). Radiographic assessment demonstrated existing primary Es and incisors with delayed eruption. This report elucidates a potential association between GPS and oral manifestations, particularly highlighting delayed eruption of primary Es. Since there is a scarcity of publications addressing the oral and dental manifestations of the syndrome, this clinical case contributes, albeit not specifically, to the diagnosis.