268 ‒ Genetics: testing, therapy, editing, association with disease risk, autism, and more

PKU is a recessive genetic metabolic disorder where the body cannot properly process phenylalanine, an amino acid. If untreated, it causes intellectual disabilities. It is managed with a lifelong, phenylalanine-restricted diet, emphasizing early diagnosis through newborn screening to prevent severe neurological damage.

Before the Human Genome Project (pre-2000s), genetic work was laborious and manual. Scientists used techniques like protein electrophoresis, enzymatic activity assays to identify conditions at the protein level, and linkage maps to crudely locate genes. DNA sequencing was manual and low-throughput, involving radioactivity and physical gel reading.

Somatic mutations occur after conception in body cells and are not passed to offspring. Germline mutations occur in egg or sperm cells and can be inherited. Mosaicism means some cells have a mutation while others don't. An individual can be a germline mosaic, meaning the mutation is in some reproductive cells and can be passed down, even if not present in all body cells of the parent.

WGS sequences all three billion base pairs of DNA (coding and non-coding regions). WES focuses only on the exome, the ~1.5% of the genome that codes for proteins. While WGS provides more complete data, WES is often a cost-effective shortcut, especially since most known disease-causing variants are in the coding regions.

The Guardian Study (Genomic Uniform Screening Against Rare Diseases In All Newborns) is a large-scale population health initiative using genome sequencing on newborn dried blood spots. It screens for treatable rare diseases with immediate interventions available, aiming to rapidly adapt to new treatments and promote health equity by identifying conditions earlier, often a decade before typical diagnosis.

A major challenge is the immune response to viral vectors like adenoviruses, which can cause severe side effects or even death, as seen in Jesse Gelsinger's case. Finding the correct therapeutic dose is tricky because an immune response often prevents subsequent treatments. New, non-viral delivery systems, like lipid nanoparticles, are being explored to mitigate these issues.

Gene addition involves introducing a new, functional gene into cells, typically for 'loss-of-function' diseases where a protein is missing. Gene editing directly fixes malfunctioning genes within the existing DNA. For sickle cell anemia, gene editing is preferred because simply adding a functional hemoglobin gene would lead to too much, still problematic, hemoglobin.

The scientific consensus is to avoid germline gene editing (changes transmissible to future generations) and 'enhancement' (improving beyond normal human traits, like intelligence or athletic ability), focusing solely on treating severe diseases in somatic cells. The concern is the unpredictable long-term effects, potential for misuse, and societal implications of creating genetic disparities.

Autism Spectrum Disorder has a high heritability (0.8-0.9), but it's not 100% genetic due to factors like prematurity and de novo mutations. Its rising prevalence is largely attributed to changing diagnostic criteria, increased recognition (especially in underserved populations), and greater motivation to seek diagnoses for access to resources, rather than solely environmental factors or genetic drift.

By 2040, diagnosis is expected to be trivial due to falling sequencing costs and advancements in machine learning and AI, making it more accessible globally. The pace of therapeutic development is harder to predict, but there is optimism for catalytic breakthroughs that will scale gene therapies, although the challenge of affordability for widespread implementation remains significant.

The liver is considered a relatively easy organ to target for gene therapy because it acts as the body's metabolic clearinghouse. Many genes involved in inborn errors of metabolism are expressed in the liver, and some common viral vectors and delivery systems are well-suited to reach liver cells effectively.

Current gene therapies are very expensive, ranging from $1 million to $3 million per treatment. While this is prohibitive for widespread use, it's argued that a one-time gene therapy offering decades of life extension in infancy, like for SMA, can be more cost-effective over a lifetime than prolonged treatments like chemotherapy for cancer.