MedGen

Autosomal recessive congenital ichthyosis (ARCI) encompasses several forms of nonsyndromic ichthyosis. Although most neonates with ARCI are collodion babies, the clinical presentation and severity of ARCI may vary significantly, ranging from harlequin ichthyosis, the most severe and often fatal form, to lamellar ichthyosis (LI) and (nonbullous) congenital ichthyosiform erythroderma (CIE). These phenotypes are now recognized to fall on a continuum; however, the phenotypic descriptions are clinically useful for clarification of prognosis and management. Infants with harlequin ichthyosis are usually born prematurely and are encased in thick, hard, armor-like plates of cornified skin that severely restrict movement. Life-threatening complications in the immediate postnatal period include respiratory distress, feeding problems, and systemic infection. Collodion babies are born with a taut, shiny, translucent or opaque membrane that encases the entire body and lasts for days to weeks. LI and CIE are seemingly distinct phenotypes: classic, severe LI with dark brown, plate-like scale with no erythroderma and CIE with finer whiter scale and underlying generalized redness of the skin. Affected individuals with severe involvement can have ectropion, eclabium, scarring alopecia involving the scalp and eyebrows, and palmar and plantar keratoderma. Besides these major forms of nonsyndromic ichthyosis, a few rare subtypes have been recognized, such as bathing suit ichthyosis, self-improving collodion ichthyosis, or ichthyosis-prematurity syndrome. [from GeneReviews]

Schizophrenia is highly heritable, as shown by family, twin, and adoption studies. For example, for identical twins, if one twin develops schizophrenia, the other twin has about a 50% chance of also developing the disease. The risk of the general population developing the schizophrenia is about 0.3-0.7% worldwide. The search for “schizophrenia genes” has been elusive. Initial linkage studies looked at parts of the genome associated with schizophrenia, and many candidate genes were identified, including APOE, COMT, DAO, DRD1, DRD2, DRD4, DTNBP1, GABRB2, GRIN2B, HP, IL1B, MTHFR, PLXNA2, SLC6A4, TP53, and TPH1. However, some of these have later been questioned. Microdeletions and microduplications have been found to be three times more common in individuals with schizophrenia, compared to controls. Because these deletions and duplications are in genes that are overexpressed in pathways related to brain development, it is possible that the inheritance of multiple rare variants may contribute to the development of schizophrenia. Several genetic disorders feature schizophrenia as a clinical feature. The 22q11.2 Deletion Syndrome comprises many different syndromes, of which one of the most serious is DiGeorge syndrome. Children born with DiGeorge syndrome typically have heart defects, cleft palate, learning difficulties, and immune deficiency. Schizophrenia is a late manifestation, affecting around 30% of individuals. Microdeletions and duplications in chromosome 1, 2, 3, 7, 15 and 16 have also been associated with schizophrenia. In 2014, a genome-wide association study looked at the genomes of over 35,000 patients and 110,00 controls. The study identified 108 SNPs that were associated with schizophrenia, 83 of which had not been previously reported. As expected, many of these loci occurred in genes that are expressed in the brain. For example, the SNPs included a gene that encodes the dopamine D2 receptor, DRD2 (the target of antipsychotic drugs), and many genes involved in glutamine neurotransmitter pathways and synaptic plasticity (e.g., GRM3, GRIN2A, SRR, GRIA1). More surprisingly, however, associations were also enriched among genes expressed in tissues with important immune functions. In 2016, a study based on nearly 65,000 people investigated the association between schizophrenia and variation in the Major Histocompatibility Complex (MHC) locus—a region on chromosome 6 that is important for immune function. The study focused on the C4 gene (complement component 4) that exists as two distinct genes: C4A and C4B, which encode particularly structurally diverse alleles. The study found that the alleles which promoted greater expression of C4A in the brain were associated with a greater risk of schizophrenia. By using mice models, the study showed that C4 is involved in the elimination of synapses during brain maturation. In humans, “synaptic pruning” is most active during late adolescence, which coincides with the typical onset of symptoms of schizophrenia. It is therefore possible that the inheritance of specific C4A alleles could lead to “run away” synaptic pruning, increasing the risk of schizophrenia. Further research may even determine C4 as a potential therapeutic target. [from Medical Genetics Summaries]

Bipolar disorder is an illness of mood characterized by alternating episodes of elevated and depressed moods, which are interspersed with euthymic periods. [from HPO]

Autism spectrum disorder (ASD) is a condition that appears very early in childhood development, varies in severity, and is characterized by impaired social skills, communication problems, and repetitive actions. These difficulties can interfere with affected individuals' ability to function in social, academic, and employment settings. People with ASD also have an increased risk of psychiatric problems such as anxiety, depression, obsessive-compulsive disorder, and eating disorders.

From as early as 1 to 2 years of age, people with ASD have an impaired ability to interact with other people; they are often more comfortable dealing with objects. Affected individuals have difficulty understanding and using non-verbal social cues such as eye contact, facial expressions, gestures, and body language. Inability to recognize and use these cues makes it hard for affected individuals to understand the feelings of others or communicate their own feelings appropriately. Signs of ASD, such as reduced eye contact and social interaction, can sometimes be detected before age 2. However, the condition is usually diagnosed between ages 2 and 4, when more advanced communication and social skills, such as learning to play with others, typically begin to develop.

Repetitive actions in ASD can include simple actions such as rocking, hand-flapping, or repetition of words or noises (echolalia). Affected individuals often dwell on or repeatedly express particular thoughts; this trait is called perseveration. People with ASD tend to be rigid about their established routines and may strongly resist disruptions such as changes in schedule. They may also have difficulty tolerating sensory stimuli such as loud noises or bright lights.

While social and communication difficulties and unusual actions define ASD, affected individuals can have a wide range of intellectual abilities and language skills. A majority of people with ASD have mild to moderate intellectual disability, while others have average to above-average intelligence. Some have particular cognitive abilities that greatly surpass their overall level of functioning, often in areas such as music, mathematics, or memory.

Some people with ASD do not speak at all, while others use language fluently. However, fluent speakers with ASD often have problems associated with verbal communication. They might speak in a monotone voice, have unusual vocal mannerisms, or choose unusual topics of conversation.

Several diagnoses that used to be classified as separate conditions are now grouped together under the diagnosis of ASD. For example, autistic disorder was a term that was used when affected individuals had limited or absent verbal communication, often in combination with intellectual disability. By contrast, Asperger syndrome was a diagnosis formerly applied to affected individuals of average or above-average intelligence who were not delayed in their language development. The broader diagnosis of ASD was established because many affected individuals fall outside of the strict definitions of the narrower diagnoses, and their intellectual and communication abilities may change over time. However, some individuals who were previously diagnosed with one of the subtypes now do not meet all the criteria of the new umbrella diagnosis. [from MedlinePlus Genetics]

Persistent deficits in social interaction and communication and interaction as well as a markedly restricted repertoire of activity and interest as well as repetitive patterns of behavior. [from HPO]

Atrial septal defect (ASD) is a congenital abnormality of the interatrial septum that enables blood flow between the left and right atria via the interatrial septum. [from HPO]