XLH is a genetic condition that’s linked to the X chromosome. We each inherit two sex chromosomes — usually XX if female and XY if male — and XLH is passed on through changes in genes carried on the X chromosome.

In X-linked dominant conditions like XLH, only one copy of the altered gene is needed for someone to have the condition. This means XLH can be passed on by either parent.

• A woman with XLH has a 50% chance of passing XLH on to each child, regardless of sex.

• A man with XLH will always pass XLH to his daughters, but not to his sons.

If you’d like to explore how genes are inherited in more detail, the Learn Genetic website offers clear, accessible explanations  https://learn.genetics.utah.edu/

There is very little research about puberty in people with XLH. What we do know suggests that, much like the general population, the timing of puberty is influenced by genetics, environment and weight.

All contraceptives available in the UK are safe for people with XLH, as long as your other health conditions allow. They do not interact with burosumab, and can be used whether you are on burosumab or not.

For women with very stiff hips, it may be helpful to know that most contraceptive coils are inserted in the lithotomy position (lying on your back with your legs supported in stirrups). If hip stiffness makes this position uncomfortable or difficult, speak to your GP. You may be referred to a gynaecology service or a sexual health clinic, where additional pain relief options—such as gas and air—are often available.

If these measures are still not enough, coils can be fitted under anaesthetic. This does carry its own risks, but please don’t be put off seeking advice or support with contraception because you have XLH. You deserve safe, comfortable access to the full range of contraceptive choices.

As far as we know, women with XLH have the same chances of conceiving naturally as the general population. There is no evidence to suggest reduced fertility.

Some people choose to explore IVF. IVF is available to women with XLH because it is a known genetic condition. Pre‑Implantation Genetic Testing (PGT‑M) can be used to identify whether an embryo carries the XLH gene. Embryos that do carry the gene are not implanted.

If you would like to discuss IVF, your GP or your XLH specialist team can refer you for genetic counselling. Attending counselling does not mean you must proceed with IVF—it is simply an opportunity to explore your options.

Amy’s Story

Many people explore different paths when planning a family, and hearing from others can be reassuring. Amy, who lives with XLH, chose IVF with PGT‑M to ensure her daughter did not inherit the XLH gene.

In this short video, Amy shares her experience and the considerations that shaped her decision. XLH UK is grateful to Joe Bonnell and Rachel Lewis for their expertise in creating this film.

Pregnancy brings many changes, and for someone with XLH there may be additional things to consider.

If your phosphate level is low at the start of pregnancy, your developing baby will take as much phosphate as they need, including from your bones. Bone health changes during pregnancy for everyone, as calcium is also drawn from the mother’s bones to support the growing baby.

Pregnancy places extra strain on the lower body, so if you already experience joint problems, you may find these become more noticeable. Physiotherapy and other support services are available through your midwife.

Birth choices

There is no reason you cannot have a vaginal birth with XLH if that is your preference. The lithotomy position is commonly used in the UK, but it is not the only option. If this position is uncomfortable for you, you or your birth partner can advocate for alternatives.

In some situations, lithotomy is necessary—for example, if forceps are required. If you know this position is not possible for you, it is important to include this clearly in your birth plan so your maternity team can plan ahead.

You are entitled to request a Caesarean section (C‑section) in the UK, you do not need a medical reason. Because people with XLH often struggle with mobility, having a C-section can make these difficulties worse in the short term. If you feel XLH may make a vaginal birth difficult, speak to your XLH team and ask them to liaise with your obstetric team. Anyone with an underlying condition should be under obstetric care early in pregnancy, so let your midwife know you have XLH at your booking appointment.

Medication and supplements

Burosumab should be stopped as soon as you find out you are pregnant, as it has not been tested for use during pregnancy.

All pregnant women should take vitamin D supplements. Over‑the‑counter vitamin D is usually suitable. If you feel you may need prescription‑strength vitamin D while off burosumab, speak to your XLH specialist team.

Some people need phosphate supplements during pregnancy. Your health team will advise you if this is necessary.

Breastfeeding is recommended for new mothers. If you choose to breastfeed, you can still restart burosumab. It is considered safe during breastfeeding. Only very small amounts pass into breastmilk, and any that does will be broken down in the baby’s stomach.

Breastfeeding women should continue taking vitamin D supplements.

Calcium intake is especially important when breastfeeding. The recommended intake is 1300mg per day, which is higher than for non‑breastfeeding adults. Ideally, this should come from your diet. The Royal Osteoporosis Society is a useful resource for checking your daily intake [Calcium-rich food chooser | Royal Osteoporosis Society]. If you cannot meet your needs through food alone, supplementation may be considered but you must seek guidance from your specialist team.

Menopause begins at different ages for different women. There is no evidence to suggest that women with XLH enter menopause earlier or later than the general population, although no formal studies have been carried out.

In the general population, osteoarthritis often becomes more noticeable around menopause due to hormonal changes. Women with XLH already have a higher chance of developing osteoarthritis earlier in life, so symptoms may worsen during this time.

Women with XLH do not typically develop osteoporosis. Any bone weakness is usually related to XLH itself. If you experience increased fractures around menopause, a DEXA scan may help assess bone density and quality.

Hormone Replacement Therapy (HRT) is a personal choice and is safe to take alongside burosumab. There are no known interactions.

Many women take calcium supplements around menopause to support bone health. People with XLH are not usually advised to take calcium supplements, but you can discuss this with your specialist team if you feel it may help.